DE102017214750A1 - Method and device for determining a condition of an exhaust gas treatment element for a motor vehicle - Google Patents

Abstract

A method for determining a state of an exhaust gas treatment element (100) for a motor vehicle comprises: changing a degree of moisture in a housing (102) of the exhaust gas treatment element (100), emitting microwaves (104) into the housing (102) during the loading state of the exhaust gas treatment element (100) remains within predetermined limits and after the degree of humidity has changed, - receiving microwaves (104) in response to emission, - determining a waveform (405; 406; 407) of the received microwaves (104), - determining the State of the exhaust gas treatment element (100) as a function of the determined signal course (405; 406; 407).

Description

The application relates to a method for determining a condition of an exhaust gas treatment element for a motor vehicle. The application further relates to a device which is designed to carry out a corresponding method.

Motor vehicles with petrol or diesel internal combustion engines or gas engines require various components for exhaust aftertreatment in order to comply with the statutory emission limit values. These include, inter alia, the three-way catalyst, the diesel oxidation catalyst, the nitrogen oxide storage catalyst, the SCR catalyst (selective catalytic reduction), the diesel and Otto particle filter and other systems. Several elements can also be combined, for example an SCR coating particulate filter (SDPF).

The DE 10 2014 209 305 A1 and the DE 10 2011 107 784 A1 each refer to a method for determining an aging condition of a catalyst for exhaust gas purification.

It is desirable to provide a method for determining a condition of an exhaust gas treatment element for a motor vehicle, which enables a reliable determination. Furthermore, it is desirable to provide a device that allows reliable detection.

The invention comprises a method for determining a condition of an exhaust gas treatment element for a motor vehicle and a corresponding device, which is designed to carry out the method.

In accordance with at least one embodiment, a degree of moisture in a housing of the exhaust gas treatment element is changed. Microwaves are emitted into the housing while the loading state of the exhaust treatment element remains the same within predetermined limits and after the moisture level has changed. Microwaves are received in response to the broadcast. A waveform of the received microwaves is determined. The state of the exhaust gas treatment element is determined as a function of the determined signal profile.

The exhaust gas treatment element is in particular a catalyst and / or a filter with a catalyst coating of an exhaust gas treatment system of the motor vehicle, also called exhaust aftertreatment system. For example, the filter is a particulate filter, in particular a soot particle filter. The catalyst is in particular a catalyst with a zeolite, for example an ammonia SCR catalyst. Other SCR catalysts are also possible, for example a vanadium, tungsten, titanium oxide catalyst (VWT catalyst). To reduce the nitrogen oxide concentration (NOX) in the exhaust gas of the internal combustion engine of the motor vehicle, it is possible to reduce the NOX emissions by means of the ammonia SCR catalyst. A urea water solution as a reducing agent is injected into the exhaust line. The reducing agent is vaporized and converted into gaseous ammonia (NH3). Other dosing methods are possible, for example, introduction of gaseous ammonia. The ammonia is collected in the ammonia SCR catalyst. In the ammonia SCR catalyst, the nitrogen oxides NOX are then converted into nitrogen N ₂ and water H ₂ O by means of the ammonia. NH3 is thus first adsorbed in the SCR catalyst, so stored. The possibility of NOX reduction depends on the amount of NH3 stored in the catalyst. Thus, for a reliable conversion of the NOX, it is useful to determine the amount of NH3 stored in the catalyst and to control it to a predetermined level. The storage capacity of a catalyst decreases with its aging. For the control, it is thus useful to determine the aging state of the catalyst and to be included in the scheme.

According to the application, electromagnetic waves in the microwave range are coupled into the housing of the exhaust gas treatment element for determining the state of the exhaust gas treatment element, that is, for example, the aging state of the SCR catalytic converter. The metallic housing constitutes an electrical cavity resonator. In response to the transmitted waves, a frequency spectrum is recorded either in reflection or in transmission. The properties of the spectrum change in particular with a change in the dielectric constant in the housing. The change in the dielectric constant can be determined by a change in the conductivity and / or losses or a microwave attenuation and / or a change in the quality factor Q and / or a phase change and / or a change in the resonant frequency and / or the signal propagation time (abbreviation: TDR). For example, when the amount of NH3 in the catalyst changes, a change in the received microwaves is detectable.

Electromagnetic properties inside the enclosure are affected by material changes or material inputs. The incorporation of molecules or particles such as NH3 or other liquids in the catalyst leads to a higher polarization and attenuation and thus to a higher half-width, lower frequency, quality factor Q and amplitude and changes in phase and duration of the wave.

Even a higher temperature leads to lower frequencies due to the thermal expansion of the housing. However, this can be compensated with the aid of models, for example by means of software. Further measured variables are used according to embodiments for determining the state of the exhaust gas treatment element and combined for example with operating parameters of the vehicle, for example an ambient temperature, a humidity, a loading state of a filter, a signal of a gas sensor such as a lambda probe and / or a NOX sensor ,

The exhaust gas treatment element not only absorbs NH3, but also water, in particular moisture, especially when a temperature within the housing is below 100 ° C. In a period in which the loading state of the exhaust gas element is not significantly changed, that is, for example, in which no further NH3 is metered, this effect can be utilized to determine the state of the exhaust gas treatment element. For example, the load condition will change by no more than 0.5%, not more than 1% and not more than 2% during the period.

As the moisture level in the housing changes, the catalyst thus absorbs water or moisture in addition to NH3 or instead of NH3. During this change, the waveform of the received microwaves is recorded. The waveform is characteristic of a quantity of moisture that has been absorbed during the period. In particular, if the change in the degree of moisture is known, it is possible to determine from the characteristic signal curve the storage capacity of the exhaust gas treatment element. If a lot of moisture has been absorbed by the catalyst, so the signal changes greatly, the absorption capacity of the catalyst is higher than when less moisture was absorbed and the signal changes less. Thus, it is possible to determine the state of the exhaust gas treatment element by means of the change in the degree of moisture and the evaluation of the waveform of the microwaves, for example, the aging state of an SCR catalyst.

The method using the high-frequency technique to determine the condition of the exhaust treatment element is in particular more accurate than the determination by means of a model based on signals from a wide variety of sensors and actuators of the exhaust treatment system. According to the application, the inaccuracies occurring in models can be avoided since an error chain of the individual components (motor control, temperature measurement, sensor inaccuracies, determination of the various actuator positions) is avoided.

According to at least one embodiment, the degree of humidity is increased or decreased by a predetermined value during operation of the motor vehicle. For example, defined moisture jumps, pulses and / or gradients which occur or are specifically caused in transient operation, for example by short operation with excess fuel, a modified exhaust gas recirculation rate and / or an injection of water, are used to change the degree of moisture in the housing. A lowering of the degree of moisture occurs, for example, during deceleration phases.

With an approximately constant amount of NH3 stored or in the NH3-empty state, the change in the degree of moisture in the housing is thus known. For example, this is also determined or verified by means of the lambda signals and / or other gas sensors. The determined signal waveform of the received microwaves on the change in the degree of moisture is used as a measure of the aging of the catalyst. Below, for example, it is possible to adjust the NH3 target load. If the state of aging is known, it is also possible to check the microwave system and, if necessary, to calibrate it.

In accordance with at least one further embodiment, microwaves are emitted into the housing while a temperature in the housing changes monotonously.

For example, the moisture level is increased starting at a first temperature in the housing and subsequently reduced from a second temperature. The first temperature is lower than the second temperature. As the temperature rises, the moisture level is thus first increased and subsequently reduced. The first temperature is in particular less than 100 ° C, for example between 0 ° C and 50 ° C or less. The second temperature is for example between 80 ° C and 120 ° C and in particular over 100 ° C. During a cold start, the catalyst is exposed to moisture by the cold start water present in the exhaust treatment system. As the temperature increases, this moisture is again expelled from the catalyst. Thus, a temperature-dependent water storage behavior of the catalyst can be derived from the heating curve and the determined signal profile.

In accordance with at least one embodiment, a first state of the exhaust-gas treatment element is determined as a function of the determined signal curve, which corresponds to a temperature range between the first and the second temperature. A second state of the exhaust gas treatment element is determined as a function of the determined signal profile, with a temperature range above the second temperature corresponds. Thus, depending on the temperature, it is possible to determine different states of the exhaust gas treatment element. For example, it is possible to determine a state of a surface of the catalyst in the first temperature range, since in this temperature range the surface adsorption of the moisture takes precedence. In the second temperature range, it is in particular possible to determine the storage capacity of the storage centers of the catalyst, since they primarily absorb the moisture in the second temperature range and / or interact with the moisture in an equilibrium process.

In accordance with at least one embodiment, the humidity level is increased as the temperature in the housing decreases. The signal curve is determined as a function of the decreasing temperature. For example, after switching off the internal combustion engine of the motor vehicle, the temperature is reduced. The NH3 loading in the catalyst remains constant when the internal combustion engine is switched off. The catalyst cools and absorbs the moisture contained in the exhaust line with decreasing temperature. In addition, ambient moisture diffuses from the exhaust pipe to the catalyst, which also absorbs this moisture. Thus, a temperature-dependent water storage in the catalyst can be determined. In particular, in this case a moisture sensor and / or a temperature sensor is used in order to determine the ambient humidity as accurately as possible.

In accordance with at least one embodiment, the determined signal profile is used to activate or deactivate a sensor of the motor vehicle. For example, a sensor that is sensitive to moisture and may be damaged by moisture may be deactivated depending on the detected waveform, if an increase in the degree of moisture is detected by means of the received microwaves. After a reduction in the degree of moisture has been determined and it can therefore be assumed that the water in the exhaust system has been vaporized, the sensor is activated.

Further advantages, features and developments emerge from the following, explained in conjunction with the figures examples. The same, similar and equivalent elements can be provided with the same reference numerals.

• 1 eine schematische Darstellung eines Abgasbehandlungssystems gemäß einem Ausführungsbeispiel,
• 2 eine schematische Darstellung eines Katalysators mit einer Vorrichtung gemäß einem Ausführungsbeispiel,
• 3 ein Ablaufdiagramm eines Verfahrens gemäß einem Ausführungsbeispiel,
• 4 ein Ablaufdiagramm eines Verfahrens gemäß einem Ausführungsbeispiel,
• 5 eine schematische Darstellung von Signalverläufen gemäß einem Ausführungsbeispiel, und
• 6 ein Ablaufdiagramm eines Verfahrens gemäß einem Ausführungsbeispiel.

Show it:

• 1 a schematic representation of an exhaust treatment system according to an embodiment,
• 2 a schematic representation of a catalyst with a device according to an embodiment,
• 3 a flowchart of a method according to an embodiment,
• 4 a flowchart of a method according to an embodiment,
• 5 a schematic representation of signal waveforms according to an embodiment, and
• 6 a flowchart of a method according to an embodiment.

1 shows an exhaust treatment system 120 for an internal combustion engine 105 , Exhaust gases of the internal combustion engine 105 be in an exhaust system 107 brought in. The exhaust gases are by means of an exhaust gas treatment element 100 cleaned before passing through the exhaust tailpipe 108 be discharged into the environment. The exhaust treatment element 100 is with a device 110 coupled. One or more sensors 106 and 109 are provided. The sensors 106 . 109 are for example gas sensors such as lambda sensor or NOX sensor. In particular, the sensor 106 may also be another sensor, in particular a sensor sensitive to moisture and should be protected for reliable operation against moisture deposits during operation.

2 shows the exhaust treatment element 100 according to an embodiment. The exhaust element 100 is in particular part of the exhaust treatment system 120 , also called exhaust aftertreatment system. The exhaust treatment element 100 For example, a catalyst or a combination of a catalyst and a particulate filter. For example, the exhaust gas treatment element 100 a hydrocarbon absorber or an ammonia SCR catalyst.

In a metallic housing 102 the exhaust treatment element 100 is an exhaust treatment module 101 arranged. The exhaust treatment module 101 For example, it is used to store ammonia. The exhaust treatment element 100 and the exhaust treatment module 101 are thus set up to be loaded with ammonia.

The loading state can be determined well with high-frequency measurement technology, in particular with microwaves 104 , The microwaves are for example in a range between 300 MHz and some 100 GHz. In particular, according to the application, a frequency range of about 0.3 GHz to 10 GHz, for example, from 1.5 GHz to 7 GHz used. Other frequency ranges are possible.

To send and receive microwaves 104 In the embodiment shown, a first and a second transmitting and receiving device 103 intended. These are, for example, each high-frequency antennas, which are coupled to a corresponding exciter, for example with an oscillator. The coupling can be done electrically and / or inductively. The microwaves are received, for example, after transmission and / or after reflection.

According to further embodiments is only a single transmitting and receiving device 103 intended. This first sends the microwaves 104 out in the case 102 be reflected and subsequently again from the transmitting and receiving device 103 be received.

The device 110 is for example part of an engine control of the motor vehicle. The device 110 Among other things, it is used to evaluate the received microwaves 104 , The device 110 is according to embodiments also with the sensors 106 and 109 signal-technically coupled.

The permittivity and conductivity in the exhaust gas treatment element 100 depends on the loading condition, ie in particular how much liquid in the module 101 is stored. The module 101 In particular, both ammonia and water can store or interact with ammonia and water.

In particular, a change in the propagation of the microwaves 104 in the case 102 that the microwaves interact with the NH3 molecules and / or water or moisture in so-called acid storage centers on the module surface, since the module 101 due to the NH3 molecules and / or due to the water becomes electrically conductive. Thus, if the catalyst loses storage centers, for example due to aging, ie its storage capacity, in particular its NH3 storage capacity, this is also reflected in a reduced influence of water. A loading of the catalyst consequently has less influence on the propagation of the microwaves 104 ,

3 shows a method for determining a condition of the exhaust treatment element 100 , in particular a state of aging.

In step 301 First, a degree of humidity in the housing 102 and thus in the module 101 changed. In particular, the change in the degree of moisture is known. For example, water is injected specifically during the transient operation. Even a short operation with excess fuel and / or a modified exhaust gas recirculation rate can be used to bring about the defined change in humidity. In addition, during the change in the degree of moisture, the amount of NH3 in the exhaust gas treatment element 100 not changed outside the predetermined limits, so that an approximately constant, known amount of NH3 in the exhaust gas treatment element 100 is present. It is also possible to take the step 301 to start after the exhaust treatment element 100 was completely emptied and the amount of NH3 is therefore zero. The change in the degree of moisture is according to embodiments, for example by means of the sensor 109 verified, which is for example a lambda probe or another gas sensor.

In step 302 following the step 301 or can be done simultaneously, the load measurement by means of microwaves 104 carried out. In particular, the measurement is performed once before the change in the degree of humidity and once after and compared the two waveforms determined. In step 303 is determined from the determined waveform, how much moisture the exhaust gas treatment element 100 has recorded. In particular, it is compared what proportion of the introduced moisture from the exhaust gas treatment element 100 has been recorded.

In step 304 the condition of the exhaust gas treatment element is determined from the recorded moisture determined by means of the signal curve 100 determines, for example, the state of aging. If a comparatively high proportion of the introduced moisture in the exhaust gas treatment element 100 has been recorded, and the signal has consequently changed greatly, it is concluded that there is a low degree of aging. If comparatively little of the introduced moisture in the exhaust gas treatment element 100 has been stored, and the signal has consequently changed little, is concluded that a high degree of aging. In the high state of aging is in particular a lower storage capacity of the exhaust gas treatment element 100 available.

4 shows a method for determining the condition of the exhaust treatment element 100 according to a further embodiment.

In step 401 First, the degree of moisture in the exhaust gas treatment element 100 elevated. At the same time, the temperature in the exhaust gas treatment element becomes 100 increased, for example, from a first temperature 408 to a second temperature 409 ( 5 ). For example, is used in a cold start of the engine, that in the exhaust treatment system 120 , especially in the exhaust system 107 Water is that deposits in the exhaust gas treatment element. With rising temperature in the exhaust gas treatment element 100 This moisture is expelled from the catalyst again. Thus, for example, increases the resonance frequency, as in the waveform 405 between the first temperature 408 and the second temperature 409 recognizable ( 5 ).

Depending on how much water in the exhaust treatment element 100 has been stored, the resonance frequency or one of the other already mentioned parameters of the microwaves changes 104 different strengths. Within the limits of non-changing NH3 loading can thus be the state of the exhaust gas treatment element 100 determine.

In particular, a state of the surface of the module can be 100 determine, since in the temperature range below the second temperature 409 the water primarily on the surface of the module 100 condensed. Thus, for example, surface defects can be determined, which have arisen due to overheating.

At a further temperature rise above the second temperature 409 will be in step 403 that is, the degree of moisture in the exhaust gas treatment element 100 again reduced. Here, too, can be derived from the change in the signal curve 405 determine how much water in the exhaust gas treatment element 100 has been stored, in particular until stationary operating points 407 are reached.

In step 403 can thus be dependent on the detected signal waveform 405 For example, compared to stored reference curves, or by comparison with historical waveforms, the condition of the exhaust treatment element 100 or several different states of the exhaust treatment element 100 determine.

The temperature-dependent water storage behavior of the exhaust gas treatment element 100 can be calculated from the heating curve and the corresponding signal curve 405 derived.

In particular, show different memory centers of the module 101 at different temperatures an increased water desorption, which is characteristic of the catalyst and its state of aging. Thus, depending on the temperature of the state of the different storage centers can be determined.

Even with a warm start, differences in the absorption of moisture can be determined. A warm start will be a signal waveform 406 determined, depending on the recorded moisture, for example, at different resonance frequencies.

The exhaust gas humidity and absolute amount of water in the exhaust system 107 is, for example, during the warm-up phase between the first temperature 408 and the second temperature 409 by means of the lambda probe 109 , a mass flow sensor and / or a temperature sensor can be determined. For example, the first temperature 408 and the second temperature 409 higher than in 5 located. For example, the first temperature is 408 at about 100 ° C and the second temperature 409 is between 105 ° C and 200 ° C, for example at about 160 ° C.

The temperature-dependent high-frequency signal with the waveform 405 additionally contains information about the dew point behavior. In particular, after the local maximum at about the second temperature 409 has been exceeded or if the stationary operating points 407 are reached, it can be assumed that all cold start water or other water in the exhaust system 107 was evaporated. Consequently, sensors such as the sensor can subsequently be used 106 be activated, for example, heated, which could otherwise be damaged in contact with water.

6 shows a flowchart of a method for determining the exhaust gas treatment element 100 according to a further embodiment.

In step 601 becomes the internal combustion engine 105 off. Subsequently, the temperature in the exhaust gas treatment element decreases 100 , The NH3 loading remains constant and the catalyst cools.

In step 602 takes the exhaust treatment element 100 during the decreasing temperature in the exhaust system 107 contained moisture on. In the course of ambient humidity diffused from the exhaust pipe 108 to the exhaust treatment element 100 , which at least partially absorbs the further moisture. Thus, a temperature-dependent water storage of the exhaust gas treatment element can be 100 determine.

In step 603 becomes the waveform of the received microwaves 104 evaluated. Depending on the catalyst 100 recorded moisture changes the waveform, because the conductivity is increased with increasing absorption of moisture. As a result, the microwave signal is more attenuated as the absorption of moisture increases. In particular, the moisture in the exhaust system 107 and the ambient humidity determined by means of other sensors such as a humidity sensor and / or a temperature sensor to determine how much moisture theoretically from the exhaust gas treatment element 100 be recorded could. When much of the moisture has been absorbed, a low degree of aging is assumed. If a little of the existing moisture was absorbed, is on a lower storage capacity of the exhaust gas treatment element 100 and thus concluded a high degree of aging.

In addition to determining the catalyst aging, the information according to exemplary embodiments is used to determine the sensor signal behavior and, if necessary, to calibrate it. For example, a zero point for the NH3 loading can be reset if it is known that the exhaust gas treatment element 100 was completely freed from ammonia. Alternatively or additionally, it is possible for the aging effects, for example, in the device 120 to deposit and when metering ammonia in the exhaust system 107 to take into account.

The method according to the application therefore uses the moisture dependency of the microwave signal, in particular the moisture dependence of the frequency, the amplitude, the quality, the phase, the propagation velocity, the average values of the respective quantities and / or further statistically derivable values of the basic parameters in transmission and / or reflection measurement Viewing one or more scattering parameters to account for the aging condition of an exhaust treatment element 100 in particular the aging state of an SCR catalytic converter. This includes, for example, an NH3 storage capability and / or a microwave signal behavior. Depending on the determined NH3 storage capacity, for example, an NH3 target load is adjusted. Depending on the detected microwave signal behavior, for example, the microwave sensor signal is recalibrated. For example, a change in humidity in the exhaust gas is used during the conventional operation of the internal combustion engine 105 occurs. Alternatively or additionally, the moisture change in the exhaust gas is specifically caused. The NH3 loading in the exhaust gas treatment element 100 is kept almost constant.

Alternatively or additionally, the cold start signal behavior and / or the warm start signal behavior with the Katalysatoraufheizkurve is used. During cold start, the catalyst 100 increased charged with starting water and this by heating 100 Temperature dependent again removed from the catalyst. The temperature-dependent water storage and -ausspeicherung is according to embodiments in addition to the dew-point release of other sensors such as the sensor 106 used.

Alternatively or additionally, the cooling behavior and moisture storage behavior after switching off the internal combustion engine 105 used. The NH3 loading remains constant and in the exhaust system 107 containing and from the tailpipe 108 to the catalyst 100 diffusing moisture interacts with the catalyst 100 , As the temperature decreases, more water will be on the module 101 stored and thus enables a temperature-dependent water storage curve. In addition, it is also possible to achieve a reduction in temperature and humidity during overrun.

According to the embodiment, different aging mechanisms are used at different temperature ranges. For example, at temperatures below 100 ° C, the water reaction provides information on surface effects such as ash passivation, sintering surface losses, or similar surface modulus changes 101 , For example, at temperatures above 100 ° C, the water reaction provides information on acid sites and / or catalytically active sites of the module 101 , from which, for example, the NH3 Einspeicherfähigkeit can be derived.

From the different states, which are determined in the different temperature ranges, the accuracy of the aging determination can be increased and different aging mechanisms differentiated. The different described embodiments of the method, for example, as in terms of 3 . 4 and 5 6 and 6, can be combined in any combination to the aging determination so the determination of the state of the exhaust gas treatment element 100 be able to determine more accurately.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102014209305 A1 [0003]
• DE 102011107784 A1 [0003]

Claims (10)

A method of determining a condition of an exhaust treatment element (100) for a motor vehicle, comprising: Changing a degree of humidity in a housing (102) of the exhaust gas treatment element (100), Emitting microwaves (104) into the housing (102) while the loading state of the exhaust gas treatment element (100) remains the same within predetermined limits and after the degree of humidity has changed, Receiving microwaves (104) in response to the broadcast, Determining a signal course (405, 406, 407) of the received microwaves (104), - Determining the state of the exhaust gas treatment element (100) in dependence on the detected signal waveform (405; 406; 407). Method according to Claim 1 comprising: - increasing the degree of humidity by a predetermined value during operation of the motor vehicle. Method according to Claim 1 or 2 comprising: emitting the microwaves (104) into the housing (102) while a temperature in the housing (102) varies monotonically. Method according to one of Claims 1 to 3 comprising: - increasing the degree of humidity starting at a first temperature (408) in the housing (102), and subsequently - decreasing the degree of humidity from a second temperature (409), the first temperature (408) being less than the second temperature ( 409). Method according to Claim 4 comprising: - determining a first state of the exhaust treatment element (100) in response to the detected waveform (405; 406; 407) corresponding to a temperature range between the first (408) and second (409) temperatures, - determining a second one State of the exhaust gas treatment element (100) as a function of the determined signal profile (405; 406; 407), which corresponds to a temperature range above the second temperature (409). Method according to one of Claims 1 to 5 comprising: - increasing the degree of humidity while the temperature in the housing is decreasing; - determining the waveform (405; 406; 407) as a function of the decreasing temperature. Method according to one of Claims 1 to 6 comprising: activating a sensor (106) as a function of the determined signal profile (405; 406; 407). Method according to one of Claims 1 to 7 comprising: calibrating the exhaust treatment element (100) in dependence on the determined state. Method according to one of Claims 1 to 8th wherein determining the condition comprises: determining an ammonia storage capability of a catalyst. Device which is adapted to a method according to one of Claims 1 to 9 perform.

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