Method for operating a drive unit for a motor vehicle and corresponding drive unit

Abstract

Method for operating a drive unit (1) for a motor vehicle, which has an exhaust gas-generating drive unit and an exhaust gas aftertreatment unit (2) for aftertreating the exhaust gas, wherein for at least one exhaust gas component of the exhaust gas, a feed component present downstream of the exhaust gas aftertreatment unit (2) is determined from an input mass fraction of the exhaust gas component present upstream of the exhaust gas aftertreatment unit (2) by means of a reaction equation, wherein if a threshold value is exceeded by the feed component mass fraction, a fault of the exhaust gas aftertreatment unit (2) is detected and a fault signal is displayed and / or the drive unit is controlled in such a way that the feed component mass fraction changes in the direction of the threshold value, characterized in thatthat first a storage capacity of the exhaust aftertreatment device (2) for a further exhaust gas component is determined and calculation parameters contained in the reaction equation are determined as a function of the storage capacity of the exhaust aftertreatment device (2) for the further exhaust gas component, wherein an output rate constant, an activation energy and a reaction inhibition parameter are used as the calculation parameters.

Description

[0001] The invention relates to a method for operating a drive unit for a motor vehicle, which has an exhaust-generating drive unit and an exhaust aftertreatment device for treating the exhaust gas. For at least one exhaust gas component, a reaction equation is used to determine the output fraction of the exhaust gas component present downstream of the exhaust aftertreatment device, based on an input fraction of the exhaust gas component located upstream of the exhaust aftertreatment device. If the output fraction exceeds a threshold value, a fault in the exhaust aftertreatment device is detected, and a fault signal is displayed to the driver of the motor vehicle and / or the drive unit is controlled such that the output fraction changes in the direction of the threshold value. The invention further relates to a drive unit for a motor vehicle.

[0002] For example, the prior art includes German patent application DE 10 2004 017 274 A1. This describes a method for diagnosing emissions in a multi-row emission system, the method comprising the following steps: obtaining a large number of emission measurements, each measurement corresponding to a row of the multi-row emission system; converting each measurement into a scaled value as a percentage of a threshold; adding the scaled values ​​to obtain a total emission value for the multi-row emission system; and triggering an alert if the total emission value exceeds the threshold.

[0003] German patent application DE 10 2020 205 025 A1 relates to a method for monitoring an SCR catalyst, in which an observer determines the area factor of the SCR catalyst. A defect in the SCR catalyst is inferred if a comparison shows that the area factor falls below a threshold value.

[0004] The prior art documents DE 10 2015 203 425 A1, DE 100 38 461 A1, DE 10 2014 013 690 A1, DE 10 2014 004 714 A1 and DE 103 47 130 A1 are also known.

[0005] The object of the invention is to propose a method for operating a drive unit for a motor vehicle which has advantages over known methods, in particular enabling a reliable assessment of at least one exhaust gas component still present in the exhaust gas downstream of the exhaust gas aftertreatment device.

[0006] According to the invention, this is achieved by a method for operating a drive unit for a motor vehicle with the features of claim 1. It is provided that, first, a storage capacity of the exhaust aftertreatment device for a further exhaust component is determined, and calculation parameters included in the reaction equation are determined as a function of the storage capacity of the exhaust aftertreatment device for the further exhaust component, wherein an output velocity constant, an activation energy, and a reaction inhibition parameter are used as the calculation parameters.

[0007] Advantageous embodiments with expedient further developments of the invention are specified in the dependent claims. It should be noted that the exemplary embodiments described in the description are not limiting; rather, any variations of the features disclosed in the description, the claims, and the figures are possible.

[0008] The drive system serves to propel the motor vehicle, thus providing the drive torque directed towards propelling the vehicle. To provide this drive torque, the drive system comprises the drive unit. During operation, the drive unit is supplied with fuel and fresh gas, at least intermittently, whereby the fresh gas contains fresh air, at least intermittently. Additionally, the fresh gas may contain exhaust gas if exhaust gas recirculation is implemented, in which the exhaust gas generated by the drive unit is at least partially returned to the drive unit as a component of the fresh gas. The fuel and fresh gas supplied to the drive unit form a fuel-fresh gas mixture with a specific composition, which is then reacted within the drive unit.

[0009] During operation of the engine, exhaust gas is produced due to the chemical reaction of fuel and fresh air. This exhaust gas is discharged towards the outside environment of the engine or vehicle. Since the exhaust gas generated by the engine contains pollutants, it is first routed to an exhaust aftertreatment system before being released into the environment. In the exhaust aftertreatment system, the pollutants are at least partially converted into less harmful products. Only after passing through the exhaust aftertreatment system is the exhaust gas released into the environment.

[0010] The exhaust aftertreatment system is, for example, a vehicle catalyst, in particular a three-way catalyst, oxidation catalyst, NO xThe exhaust aftertreatment system can be a storage catalyst or an SCR catalyst. It can also be designed as a particulate filter, particularly a gasoline particulate filter or a diesel particulate filter, preferably with an integrated vehicle catalyst, for example, with a catalytic coating. The conversion rate, and thus the conversion capacity of the exhaust aftertreatment system, which converts the pollutants into less harmful products, depends in particular on the composition of the exhaust gas supplied to the system and / or on the storage load of the exhaust aftertreatment system, which in turn is related to the composition of the exhaust gas. Storage load refers to the amount of the additional exhaust gas component temporarily stored in the exhaust aftertreatment system.Additionally, the condition of the exhaust aftertreatment system affects the conversion rate. This condition refers in particular to an aging state that steadily deteriorates over the service life of the exhaust aftertreatment system.

[0011] The exhaust aftertreatment system has a specific storage capacity for the additional exhaust component. The additional exhaust component is understood to be an exhaust component that can correspond to, but preferably differs from, the at least one other exhaust component. For example, the additional exhaust component is oxygen, particularly if the drive unit is a gasoline engine. If, on the other hand, the drive unit is a diesel engine, the additional exhaust component is preferably ammonia. In the latter case, the aforementioned SCR catalyst is particularly preferably used as the exhaust aftertreatment system.

[0012] The condition of the exhaust aftertreatment system is determined by first measuring its storage capacity, in particular its oxygen or ammonia storage capacity. The system's condition can then be derived from this measurement. Preferably, a defect in the exhaust aftertreatment system is detected as soon as the storage capacity falls below a certain threshold.

[0013] Due to increasingly stringent emissions regulations, it is necessary to determine the quantity of pollutants present downstream of the exhaust aftertreatment system. This can be done, for example, by taking measurements. However, this is complex, especially if measurements would have to be taken for a large number of exhaust gas components. In many cases, measurement is also not practically feasible. For this reason, it is planned to perform a calculation for at least one exhaust gas component. An exhaust gas component is essentially any constituent of the exhaust gas, particularly a component whose initial mass fraction is not measured, or cannot be measured, downstream of the exhaust aftertreatment system.

[0014] The calculation is based on the input fraction of the exhaust gas component present upstream of the exhaust aftertreatment system. The input fraction describes the proportion of the exhaust gas component's amount of substance to the total amount of substance in the exhaust gas. The input fraction is expressed as a mole fraction and thus quantitatively describes the composition of the exhaust gas. From the input fraction, the output fraction of the exhaust gas component present downstream of the exhaust aftertreatment system is determined. The output fraction also quantitatively describes the composition of the exhaust gas, relating the amount of substance of the exhaust gas component downstream of the aftertreatment system to the total amount of substance in the exhaust gas present there. The output fraction is also expressed as a mole fraction.

[0015] The determination of the feed fraction from the input fraction is carried out using the reaction equation. This equation describes the change in the mole fraction of the exhaust gas component as the exhaust gas passes through the aftertreatment system. However, since the conversion rate or conversion capacity of the aftertreatment system changes over time, the reaction equation must be adjusted to reflect the current state of the system in order to determine the feed fraction with high accuracy.

[0016] For this reason, the calculated parameter included in the reaction equation is determined based on the storage capacity of the exhaust aftertreatment system. By incorporating the storage capacity of the exhaust aftertreatment system into the reaction equation, the accuracy of the calculated feedstock fraction is significantly increased. Specifically, the reaction equation is adjusted towards higher reaction rates as the storage capacity increases. Conversely, the reaction equation is adjusted towards lower reaction rates as the storage capacity decreases. Consequently, the aging of the exhaust aftertreatment system is reliably accounted for.

[0017] According to the invention, a fault in the exhaust aftertreatment system is detected when a threshold value is exceeded by the proportion of the exhaust gas. In this case, for example, a fault signal is displayed to the driver of the vehicle and / or the drive unit is controlled in such a way that the proportion of the exhaust gas changes towards the threshold value, in particular down to this value. If the proportions of the exhaust gas components of several components are determined, preferably a separate threshold value is assigned to each component, against which the respective proportion of the exhaust gas is compared.

[0018] It may be possible to determine the throughput of the exhaust component from the initial mass fraction and a mass flow rate of the exhaust gas, in particular the exhaust gas mass flow. Preferably, the throughput is integrated over time to obtain a quantity of the exhaust component. From this quantity, a distance-related quantity can be determined using the distance traveled by the vehicle during that time, for example, in the unit g / km. The distance-related quantity is then compared with a threshold value, and if the distance-related quantity exceeds the threshold, a fault in the exhaust aftertreatment system is detected.

[0019] The invention provides that the following parameters are used as calculation parameters: initial rate constant, activation energy, and reaction inhibition parameter, optionally a rate constant and / or adjustment parameter. The rate constant refers in particular to the rate constant of the chemical reaction occurring for the exhaust gas component in the exhaust aftertreatment system. The rate constant is typically temperature-dependent and is therefore available at least as a function of temperature and, in this case, additionally as a function of the storage capacity.

[0020] The velocity constant can be divided into the output velocity constant and the adjustment parameter, or determined from these quantities. Preferably, the velocity constant is obtained by multiplying the output velocity constant by the adjustment parameter. The output velocity constant describes the velocity constant at a defined temperature, in particular at an output temperature T0. The output temperature preferably corresponds to a temperature under standard conditions, for example, 0 °C or 20 °C. The output velocity constant is thus defined for a constant temperature and is therefore, for a given exhaust gas component, dependent only on the storage capacity.

[0021] The adjustment parameter describes the influence of temperature on the rate constant, starting from the initial rate constant. It is based, in particular, on the initial temperature and the current temperature. The adjustment parameter depends on the temperature and the storage capacity. Additionally, the activation energy can be incorporated into the adjustment parameter. Activation energy is the energy that must be overcome for the chemical reaction described by the reaction equation to proceed. For a given exhaust gas component, the activation energy depends solely on the storage capacity.

[0022] Finally, the reaction inhibition parameter describes the influence of the instantaneous fill level of the exhaust aftertreatment system containing the additional exhaust gas component on the reaction rate or the rate constant. The reaction inhibition parameter is preferably dependent on both the fill level and the storage capacity, or is a function of these. At least one of the aforementioned parameters is considered in the reaction equation. For example, however, several or even all of the parameters are used in the reaction equation to determine the initial molar fraction of the exhaust gas component. According to the invention, the initial rate constant, the activation energy, and the reaction inhibition parameter are used in the reaction equation as calculation parameters dependent on the storage capacity. This results in particularly high accuracy.

[0023] A further development of the invention provides that the rate constant is determined from the initial rate constant and the adjustment parameter. This has already been mentioned. The rate constant is obtained, in particular, by multiplying the initial rate constant by the adjustment parameter. The adjustment parameter can also be referred to as the reaction rate factor. The use of these two parameters to determine the rate constant enables high accuracy in determining the molar fraction of the reactant.

[0024] A further development of the invention provides that the rate constant is corrected using the reaction inhibition factor. It has already been mentioned that the storage level can influence the reaction rate. This is taken into account via the reaction inhibition factor, which is determined from the storage level. Preferably, the calculated value used in the reaction equation is obtained by multiplying the rate constant by the reaction inhibition factor, or the reaction rate used in the reaction equation is corrected by multiplying it by the reaction inhibition factor. This also results in the aforementioned high accuracy.

[0025] A further development of the invention provides that the calculation parameters are determined as a function of the storage capacity by means of a mathematical relationship, a characteristic map, or a table. The mathematical relationship, characteristic map, or table takes the storage capacity as its input and at least one calculation parameter as its output. If several calculation parameters are used in the reaction equation, a separate mathematical relationship, characteristic map, or table is preferably provided for each of the calculation parameters used.

[0026] For example, characteristic maps are used for all calculation parameters. However, it is also possible to determine one of the calculation parameters using a characteristic map and another using a mathematical relationship or a table. The mathematical relationship, the characteristic map, or the table is preferably stored at the factory in the drive unit or a control unit of the drive unit, and in particular, it is permanently stored. The described procedure enables the precise determination of the initial mass fraction of the exhaust gas component.

[0027] A further development of the invention provides that one of the following components is used as at least one exhaust gas component: hydrocarbon, in particular total hydrocarbon, carbon oxide, in particular carbon monoxide and / or carbon dioxide, hydrogen, methane, ammonia, oxygen, and nitrogen oxide, in particular nitrogen monoxide and / or nitrogen dioxide. The term hydrocarbon is understood to mean any hydrocarbon, for example, methane. However, total hydrocarbon (THC) is particularly preferred, i.e., several or all of the hydrocarbons present in the exhaust gas.

[0028] The determination of the feed fraction from the respective input fraction is carried out for at least one of the aforementioned exhaust gas components, but preferably for several of the components. It is particularly preferred that this is done for all of the aforementioned components. This means that for each of the aforementioned components, the respective feed fraction is determined from the respective input fraction, namely using a respective reaction equation with a respective calculation parameter that is determined as a function of the storage capacity of the exhaust aftertreatment system. Consequently, the feed fractions of numerous different exhaust gas components downstream of the exhaust aftertreatment system are known.

[0029] A further development of the invention provides that the input mass fraction is determined for a currently existing operating point of the drive unit. The input mass fraction corresponds to a raw emission of the exhaust gas component from the drive unit, i.e., the mass fraction of the exhaust gas component in the exhaust gas flow between the drive unit and the exhaust aftertreatment device. The input mass fraction is determined for at least one exhaust gas component for the currently existing operating point of the drive unit, wherein the operating point is characterized in particular by a rotational speed of the drive unit and / or a drive torque provided by the drive unit.

[0030] The determination of the input mass fraction is preferably carried out using a mathematical relationship, a characteristic map, or a table, with the operating point being used as the input variable and the input mass fraction as the output variable. This approach enables the determination of the input mass fraction for at least one exhaust gas component with high accuracy and, correspondingly, a precise determination of the output mass fraction.

[0031] A further development of the invention provides that the reaction equation is the relationship y2=y1e−(k(T0)eER(1T0−1T)Θn˙l) is used where y1 is the input mole fraction, y2 is the output mole fraction, k is the rate constant, E is the activation energy, R is the universal gas constant, T0 is the temperature at standard conditions, T is the instantaneous temperature, θ is the inhibition factor, I is a length, and ṅ is an area-related molar throughput.

[0032] The relationship is derived as follows: n˙dydl=−r, where y is the dimensionless mole fraction of the exhaust gas component and r is the reaction rate in mol / (sm³). 3 The amount-of-substance throughput has the unit mol / (sm³). 2 ). With r=k(T)y where k is the rate constant in the unit mol / (sm³). 3 ) is, consequently the relationship n˙dydl=−k(T)y

[0033] By changing the setting, you get dyy=−k(T)n˙dl

[0034] Integrating this relationship leads to... ln(y2)−ln(y1)=−k(T)n˙l

[0035] This, when rearranged, gives ln(y2y1)=−k(T)n˙l Finally, the relationship develops y2=y1 e−(K(T)n˙l)

[0036] In this, the dimensionless reaction inhibition quantity θ is also taken into account, so that one can arrive at the relationship y2=y1 e−(K(T)θn˙l) This is obtained. The velocity constant k can then be solved for in this equation, resulting in the following relationship: y2=y1 e−(k(T0)eER(1T0−1T)θn˙l)

[0037] A further development of the invention provides that the reaction equation is used for a subsection of the exhaust aftertreatment device and that the reaction equation is also used for at least one further subsection of the exhaust aftertreatment device, wherein the calculation parameters contained in the reaction equation are determined as a function of the storage capacity of the exhaust aftertreatment device, and wherein the feedstock fraction determined for the subsection is used as the input fraction for the at least one further subsection.

[0038] The reaction equation does not describe the entire exhaust aftertreatment system, but only the relevant section. Therefore, it is necessary to perform a calculation for at least one further section as well. This section and the at least one further section form part of several sections into which the exhaust aftertreatment system is divided, particularly in the direction of a main exhaust gas flow through the system.

[0039] For each of the subsections, and in particular for the subsection and the at least one further subsection, the input mass fraction and the output mass fraction are available. The input mass fraction represents the input quantity, and the output mass fraction represents the output quantity. The input mass fraction of the most upstream subsection is set equal to the input mass fraction present upstream of the exhaust aftertreatment system. The output mass fraction present downstream of the exhaust aftertreatment system is set equal to the output mass fraction of the most downstream subsection.

[0040] With the exception of the most upstream of the subsections, the input fraction for each subsection is set equal to the output fraction of the subsection immediately upstream of that subsection. The procedure for each subsection is then carried out analogously to that for the subsection itself. However, if the temperature is required, the temperature present in the respective subsection is used. This ensures a high degree of accuracy for the described method.

[0041] The invention further relates to a drive unit for a motor vehicle, in particular for carrying out the method according to the embodiments within the scope of this description, wherein the drive unit comprises an exhaust gas-generating drive unit and an exhaust gas aftertreatment device for aftertreatment of the exhaust gas. The drive unit is designed and configured to determine, for at least one exhaust gas component, a reaction equation to determine the output fraction of the exhaust gas component present downstream of the exhaust gas aftertreatment device from an input fraction of the exhaust gas component present upstream of the exhaust gas aftertreatment device.

[0042] The drive unit is further designed and configured to first determine a storage capacity of the exhaust aftertreatment system for another exhaust component and to determine calculation parameters contained in the reaction equation as a function of the storage capacity of the exhaust aftertreatment system for the other exhaust component, whereby an output velocity constant, an activation energy and a reaction inhibition parameter are used as calculation parameters.

[0043] The advantages of such a drive system design and such a procedure have already been mentioned. Both the drive system and the method for operating it can be further developed as described in this document, and reference is made to these details.

[0044] The features and combinations of features described in the description, in particular those described in the following figure description and / or shown in the figures, can be used not only in the combinations specified, but also in other combinations or individually, without departing from the scope of the invention. Thus, embodiments that are not explicitly shown or explained in the description and / or the figures, but which emerge from or can be derived from the explained embodiments, are also to be considered as encompassed by the invention.

[0045] The invention is explained in more detail below with reference to the exemplary embodiments shown in the drawing, without limiting the invention. The drawing shows: Fig. 1 a schematic representation of an area of ​​a drive unit, namely an exhaust aftertreatment unit of the drive unit, as well as Fig. 2 a schematic detailed representation of a section of the exhaust aftertreatment system.

[0046] The Fig. Figure 1 shows a schematic representation of a section of a drive unit 1 for a motor vehicle, namely an exhaust aftertreatment system 2. The exhaust aftertreatment system 2 is in the form of a vehicle catalytic converter. It has an inlet port 3 and an outlet port 4. Exhaust gas from the drive unit 1 is fed into the exhaust aftertreatment system 2 via the inlet port 3. The exhaust gas flows through the exhaust aftertreatment system 2 from the inlet port 3 towards the outlet port 4 and exits the exhaust aftertreatment system 2 through the outlet port 4 towards the outside environment.

[0047] The exhaust gas aftertreatment system 2 is divided into several subsections 5, in which catalytically active material is present. Upstream of the subsections 5, an exhaust gas component has an input material fraction y. lDownstream of the exhaust aftertreatment system, the exhaust gas component has a feedstock fraction yo. For each of the subsections 5, there is also an input fraction y1 and an output fraction y2, whereby the exhaust gas component with input fraction y1 is supplied to the subsection and with output fraction y2 is removed.

[0048] For the subsection 5 closest to the inlet port 3, the input material fraction y1 corresponds to the input material fraction y present upstream of the exhaust aftertreatment device 2. lFor the subsequent subsections 5 in the direction of exhaust gas flow, the input mass fraction y1 is set equal to the output mass fraction y2 of the immediately preceding subsection 5. The output mass fraction yo downstream of the exhaust gas aftertreatment device 2 is set equal to the output mass fraction y2 of the subsection 5 nearest the outlet connection 4.

[0049] The Fig. Figure 2 shows a schematic detail of one of the subsections 5. This has a specific length l in the main flow direction of the exhaust gas and is subjected to a specific exhaust gas mass flow, which is referred to here as the cross-sectional area-specific molar mass flow with the unit mol / (ms²). 2The figure shows that the mole fraction of the exhaust gas component decreases from the input mole fraction y1 towards the output mole fraction y2, exhibiting a specific gradient that can be expressed as dy / dl. Summing or integrating over the length l of subsection 5 yields the output mole fraction y2 from the input mole fraction y1. The described procedure allows for extremely high accuracy in determining the output mole fraction y2. REFERENCE MARK LIST: 1 Drive unit 2 Exhaust aftertreatment system 3 Inlet connection 4 Outlet connection 5 Subsection

Claims

[1] Method for operating a drive unit (1) for a motor vehicle, which has an exhaust gas-generating drive unit and an exhaust gas aftertreatment unit (2) for aftertreatment of the exhaust gas, wherein for at least one exhaust gas component of the exhaust gas, an output fraction of the exhaust gas component present downstream of the exhaust gas aftertreatment unit (2) is determined from an input fraction of the exhaust gas component present upstream of the exhaust gas aftertreatment unit (2) by means of a reaction equation, wherein if a threshold value is exceeded by the output fraction, a fault of the exhaust gas aftertreatment unit (2) is detected and a fault signal is displayed and / or the drive unit is controlled such that the output fraction changes in the direction of the threshold value, characterized by, that first a storage capacity of the exhaust aftertreatment device (2) for a further exhaust gas component is determined and calculation parameters included in the reaction equation are determined as a function of the storage capacity of the exhaust aftertreatment device (2) for the further exhaust gas component, wherein an output rate constant, an activation energy and a reaction inhibition parameter are used as the calculation parameters. [2] Method according to claim 1, characterized by , that a velocity constant is determined from the initial velocity constant and an adjustment parameter. [3] Method according to claim 2, characterized by , that the rate constant is corrected for the reaction inhibition quantity. [4] Method according to any one of the preceding claims, characterized bythat the calculation parameters are determined depending on the storage capacity by means of a mathematical relationship, a characteristic map or a table. [5] Method according to any one of the preceding claims, characterized by , that at least one of the following components is used as the exhaust gas component: hydrocarbon, carbon oxide, hydrogen, methane, ammonia, oxygen and nitrogen oxide. [6] Method according to any one of the preceding claims, characterized by , that the input material quantity fraction is determined for a currently existing operating point of the drive unit. [7] Method according to claim 2 or 3, characterized by , that the reaction equation is the relationship y2=y1e−(k(T0)eER(1T0−1T)Θn˙l) is used where y1 is the input mole fraction, y2 is the output mole fraction, k is the rate constant, E is the activation energy, R is the universal gas constant, T0 is the temperature at standard conditions, T is the instantaneous temperature, θ is the inhibition factor, l is a length and ṅ is an area-related molar throughput. [8] Method according to any one of the preceding claims, characterized by, that the reaction equation is used for a subsection (5) of the exhaust aftertreatment device (2) and the reaction equation is also used for at least one further subsection (5) of the exhaust aftertreatment device (2), wherein the calculation parameters contained in the reaction equation are determined as a function of the storage capacity of the exhaust aftertreatment device (2), and wherein the feedstock molar fraction determined for the subsection (5) is used as the input molar fraction for the at least one further subsection (5). [9] Drive unit (1) for a motor vehicle, in particular for carrying out the method according to one or more of the preceding claims, wherein the drive unit (1) has an exhaust gas generating drive unit and an exhaust gas aftertreatment unit (2) for aftertreatment of the exhaust gas, wherein the drive unit (1) is provided and configured to determine, for at least one exhaust gas component, from an input fraction of the exhaust gas component present upstream of the exhaust gas aftertreatment unit (2) by means of a reaction equation, characterized by, that the drive device (1) is further designed and configured to first determine a storage capacity of the exhaust aftertreatment device (2) for a further exhaust component and to determine calculation parameters contained in the reaction equation as a function of the storage capacity of the exhaust aftertreatment device for the further exhaust component, wherein an output velocity constant, an activation energy and a reaction inhibition parameter are used as the calculation parameters.

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