Method for controlling the exhaust gas temperature for a motor vehicle powered by an internal combustion engine, and engine control of a motor vehicle

Abstract

The invention relates to a method for controlling the exhaust gas temperature for a motor vehicle by means of a controller (2) which is incorporated in an engine control system of the motor vehicle and which comprises an inner control loop (4) for controlling a modelled ACTUAL exhaust gas temperature of an exhaust gas of an internal combustion engine and comprises an outer control loop (6) for controlling a modelled and real ACTUAL component temperature of a component that absorbs or dissipates the exhaust gas heat, wherein, when the modelled and / or real ACTUAL component temperature is detected to have reached or exceeded a stored maximum component temperature, a) the detected modelled ACTUAL exhaust gas temperature is lowered by the inner control loop (4) to a modelled TARGET exhaust gas temperature, at which the modelled ACTUAL component temperature is below the stored maximum component temperature, by reducing a modelled ACTUAL engine load of the engine to a modelled TARGET engine load of the engine and / or by increasing a modelled ACTUAL combustion air ratio to a modelled TARGET combustion air ratio; and b) a real ACTUAL engine load of the engine is adjusted to the modelled TARGET engine load of the engine, and a real ACTUAL combustion air ratio of the engine is adjusted to the modelled TARGET combustion air ratio of the engine by the engine control system by actuating the engine and / or a treatment component functionally assigned to the engine.

Description

[0001] EXHAUST GAS TEMPERATURE CONTROL METHOD FOR A

[0002] COMBUSTION ENGINE

[0003] POWERED MOTOR VEHICLE AND ENGINE CONTROL SYSTEM OF A

[0004] MOTOR VEHICLE

[0005] The invention relates to a method for exhaust gas temperature control for a motor vehicle driven by an internal combustion engine and to an engine control system of a motor vehicle on which such a method can be carried out.

[0006] Methods for exhaust gas temperature control for a motor vehicle powered by an internal combustion engine, as well as engine control systems operable according to such a method, are known in various embodiments from the prior art. These serve to regulate the temperature of components in the exhaust tract of, for example, a turbocharged, direct-injection gasoline engine in order to protect downstream components, such as the exhaust manifold, turbocharger, or catalytic converter, from thermal damage. The catalytic converter, in particular, must be protected from thermal damage or destruction.

[0007] At high load, the exhaust gases from engines can reach such a high temperature that the exhaust manifold and, in the case of turbocharged engines, the exhaust turbine, the turbocharger or the catalytic converter can be damaged.

[0008] It is known from the state of the art to install temperature sensors on the components for exhaust gas temperature control.

[0009] As soon as the temperature sensors detect that the exhaust gas temperature has reached a critical level, the conventional exhaust gas temperature control processes enrich the mixture in the engine cylinder, i.e., increase the stoichiometric ratio of fuel to air above one. This so-called enrichment has a cooling effect on the exhaust gas. However, the potential for cooling through enrichment is limited. For example, if the mixture is enriched too much, combustion misfires can occur, which can significantly impair smooth running.

[0010] If the exhaust gas temperature remains in the critical range despite increasing the air / fuel ratio to the maximum possible, turbocharged engines will switch to a lower boost pressure. The disadvantage of this is that switching to the lower boost pressure can result in a noticeable loss of engine performance for the driver.

[0011] By installing temperature sensors and by controlling the internal combustion engine-powered vehicle based on the measured exhaust gas temperature, the engine is operated with a noticeable loss of performance if the component temperature of the component is still below a critical component temperature despite the increased exhaust gas temperature.

[0012] Cooling by enrichment, i.e. increasing the stoichiometric ratio of fuel and air, is increasingly restricted by increasingly strict emissions regulations.

[0013] An object of an embodiment of the invention is to propose a method for exhaust gas temperature control for a motor vehicle driven by an internal combustion engine and an engine control of a motor vehicle on which such a method can be carried out, in which the control of the actual exhaust gas temperature is improved.

[0014] This object is achieved by a method for exhaust gas temperature control for a motor vehicle powered by an internal combustion engine, with a cascaded, decoupled control system embedded in an engine control system of the motor vehicle, which comprises an inner control loop for controlling a modeled actual exhaust gas temperature of an exhaust gas of an internal combustion engine and an outer control loop for controlling a modeled and real actual component temperature of a component that absorbs or releases exhaust gas heat, wherein at least when the modeled and / or real actual component temperature of the component is detected via a maximum component temperature stored in the engine control system by the outer control loop or by a real temperature sensor, a.the recorded modeled actual exhaust gas temperature is reduced by the inner control loop to a modeled desired exhaust gas temperature at which the modeled actual component temperature is below the stored maximum component temperature, by reducing a modeled actual engine load of the engine to a modeled desired engine load of the engine and / or by increasing a modeled actual combustion air ratio to a modeled desired combustion air ratio; and b. a real actual engine load of the engine is set to the modeled desired engine load of the engine and a real actual combustion air ratio of the engine is set to the modeled desired combustion air ratio of the engine by the engine control by controlling the engine and / or a conditioning component functionally assigned to the engine.

[0015] Because the method lowers the actual exhaust gas temperature at least when the modeled and / or actual component temperature is detected to be reached or exceeded, the motor vehicle's engine can be used more efficiently. This is because the motor vehicle's engine can be controlled in such a way that the component can be controlled within its temperature limit.

[0016] Detecting whether the modeled and / or real actual component temperature has been reached or exceeded can be done using a real temperature sensor located on or in the component. However, with the method according to the invention, the outer control loop forms a virtual temperature sensor, which allows the actual component temperature of the component to be determined without a real sensor. This allows the method to be used as a parallel simulation or calculation program by using calculations, tables, and / or characteristic maps, thus eliminating the need for additional components that would otherwise have to be installed in the vehicle.By adjusting the real ACTUAL engine load of the engine to the modeled TARGET engine load of the engine and adjusting the real ACTUAL combustion air ratio of the engine to the modeled TARGET combustion air ratio of the engine, the modeled procedure has its interface to the real values ​​of the engine control, which, after being adapted to the modeled TARGET values, are returned to the modeling, in particular the simulation, as new ACTUAL values ​​of the engine.

[0017] The adjustment of the real ACTUAL engine operating conditions to the DESIRED engine operating conditions can be done by operating the associated actuators, such as the ignition and injection system, wastegate actuator of the turbocharger

[0018] By reducing the exhaust gas temperature by reducing the engine load and / or by increasing the combustion air ratio, several options are available for reducing the exhaust gas temperature, which can be carried out in parallel or sequentially.

[0019] The term "or" is understood in its original sense. This means that the modeled actual component temperature of the component is recorded by the external control loop, and the real actual component temperature is recorded by the real temperature sensor.

[0020] In such a case, the detection of the reaching or exceeding of the modeled actual component temperature of the component via a maximum component temperature stored in the engine control system is carried out by the external control loop and / or the detection of the reaching or exceeding of the real actual component temperature of the component via a maximum component temperature stored in the engine control system is carried out by the real temperature sensor.

[0021] The term “modeling” means that the respective value or parameter or model exists purely virtually.

[0022] The term "determination" can be understood as a calculation or a comparison with a set of tables stored in the engine control system. Controlling the engine and / or a conditioning component functionally assigned to the engine by the engine control system can include changing the engine operating state, engine speed, torque requirement, relative engine load, air and fuel injection, boost pressure, ignition angle, and / or the positions of the variable intake / exhaust valves. For this purpose, the corresponding engine components in the engine and the conditioning component are controlled.

[0023] The conditioning component functionally assigned to the engine can comprise a component upstream of the engine or a component installed in or on the engine, with which the actual engine load and / or the actual combustion air ratio can be adjusted. In this case, the conditioning component can comprise a component that influences the air supply, the fuel supply, and / or the boost pressure of the engine.

[0024] In principle, it is conceivable that the aforementioned method detects the modeled actual component temperature of the component exclusively through the external control loop and, if so, whether the maximum component temperature stored in the engine control system is reached or exceeded. To improve the method, it can be provided that the real actual component temperature is detected via a real temperature sensor and compared with the modeled actual component temperature. If a deviation between the real actual component temperature and the modeled actual component temperature is detected, the models used, in particular the inversion model, can be adapted to account for the deviation.

[0025] The term “engine load” used is synonymous with the terms “air charge”, “air load” and “cylinder charge” also used in the literature.

[0026] The component can be any type of component through which the exhaust gas flows and releases or absorbs heat. For example, the component could be an exhaust manifold, a turbocharger, or a catalytic converter.

[0027] The term "combustion air ratio" refers to the ratio of the combustion air-fuel mixture in the engine cylinder. A combustion air ratio > 1 is considered enriched, a combustion air ratio = 1 is considered stoichiometric, and a combustion air ratio < 1 is considered lean.

[0028] Reducing the modeled actual engine load is limited to a maximum reduction in engine load at which driving comfort, performance and safety requirements are not or only insignificantly restricted.

[0029] Increasing the modeled actual combustion air ratio is limited to a maximum actual combustion air ratio at which a sufficiently high combustion stability is still guaranteed, at which the increased fuel consumption due to enrichment is below a defined maximum additional consumption and at which legal emission regulations are met.

[0030] It proves to be advantageous if the inner control loop for adapting the modelled engine load of the engine comprises an engine load inversion model with state feedback, if the inner control loop for adapting the modelled combustion air ratio comprises an enrichment inversion model with state feedback and / or if the inner control loop comprises an engine model in which modelled actual engine operating conditions, in particular engine operating state, engine speed, torque requirement, relative engine load, ignition angle, positions of the variable inlet / exhaust valves and / or ambient / coolant temperatures, are modelled.

[0031] The engine operating state can, for example, detect regular engine operation, the engine under full load, the engine operating to heat the catalyst, or a so-called scavenging operating state. In the scavenging operating state, the exhaust gas flow in the turbocharger is increased by adjusting the valve timing.

[0032] The engine model's task lies in calculating the actual torque / load, while the other variables are mostly consumed as input. For example, the engine speed can be determined via a crankshaft sensor, and the ignition angle and timing can be calculated using separate software algorithms in the engine control system. The engine model then calculates the resulting torque. The variable adjustments of the intake and exhaust valve openings can be determined from the positions of the variable intake / exhaust valves.

[0033] Because the inner control loop includes an engine load inversion model with state feedback, the modeled target engine load can be determined based on the recorded modeled actual exhaust gas temperature. Because the inner control loop includes an enrichment inversion model with state feedback, the modeled target combustion air ratio can be determined based on the modeled actual exhaust gas temperature.

[0034] Because the inner control loop includes an engine model, the modeled actual engine operating conditions can be adjusted to their desired engine operating conditions based on the modeled desired engine load and the modeled desired combustion air ratio and can be fed back or passed on as new actual engine operating conditions.

[0035] In the following, determination means that the output value is calculated based on the input values ​​or determined from a corresponding data set based on a characteristic map or stored in a table. In the data set, the corresponding output values ​​can be assigned and stored for each combination of input values.

[0036] In a further development of the latter method, it proves to be advantageous if the modeled target exhaust gas temperature, the modeled actual engine operating conditions and the actual combustion air ratio are supplied to the engine load inversion model as input values ​​and the modeled target engine load is determined as the output value, if the modeled target exhaust gas temperature, the modeled actual exhaust gas temperature at an actual combustion air ratio of one, the modeled actual engine speed and the relative actual engine load are supplied to the enrichment inversion model with state feedback as input values ​​and a modeled target combustion air ratio is determined as the output value and / or if the modeled target engine load and the modeled target combustion air ratio are supplied to the engine model as input values, the real and modeled actual engine operating conditions are adapted to the input values,in particular, the target engine operating conditions determined therefrom are adjusted and the adjusted modeled actual engine operating conditions are fed back as output values ​​at least to the engine load inversion model and the enrichment inversion model.

[0037] In a variant of the method, it proves to be advantageous if the inner control loop can be operated according to an engine load strategy in which the modeled actual exhaust gas temperature is first reduced by reducing the modeled actual engine load to a modeled target engine load, whereby the modeled actual combustion air ratio is set equal to one regardless of the recorded value.

[0038] If the modeled actual exhaust gas temperature is first reduced to a modeled target engine load by reducing the modeled actual engine load, it may be possible to forgo increasing the actual air combustion ratio if this already achieves the target exhaust gas temperature.

[0039] In the course of the engine load strategy, a recorded actual combustion air ratio is overridden with a value of 1 (stoichiometric mixture).

[0040] If not all control deviations can be compensated by reducing the actual engine load, the actual combustion air ratio can be reduced in a further step.

[0041] The fuel / air ratio is the ratio of fuel to air. The lambda value is the inverse of this, i.e., the ratio of air to fuel.

[0042] The reduction of the modeled actual engine load is limited to a maximum reduction of the modeled actual engine load up to which safety and drivability requirements can be guaranteed.

[0043] This maximum reduction of the actual engine load can be calibrated.

[0044] Alternatively or in addition to the aforementioned embodiments, the inner control loop can be operated according to an enrichment strategy in which the desired exhaust gas temperature is first reduced by increasing the modeled actual combustion air ratio, whereby the maximum enrichment of the modeled combustion air ratio is unaffected by the modeled actual engine load.

[0045] In such a case, enrichment is applied first and the remaining control deviation is compensated by reducing the air torque, i.e. by reducing the actual engine load.

[0046] In this case, the combustion air ratio provided to the engine load inversion model is overwritten with a value corresponding to the maximum value of the modeled actual combustion air ratio. This allows the engine load inversion model to detect the temperature reduction effect caused by increasing the actual combustion air ratio and then only compensates for the remaining control deviation.

[0047] Increasing the modeled actual combustion air ratio is calibratable, but limited due to emission and fuel consumption aspects as well as effects on combustion stability.

[0048] By overwriting the combustion air ratio input in the engine load inversion model with the maximum value, a desired engine load can result that is greater than the actual engine load, at least as long as the enrichment is below the calibrated limit, since the engine load inversion model "sees" more enrichment than is actually provided.

[0049] This does not lead to an increase in engine load at an air / fuel ratio lower than the maximum air / fuel ratio, as the engine model or a torque model selects a minimum of loads. This signal arbitration results in the desired behavior of reducing engine load only when the maximum air / fuel ratio is reached.

[0050] Furthermore, it proves to be advantageous if, at a combustion air ratio of one, the engine load inversion model with state feedback solely lowers the modeled target exhaust gas temperature by reducing the modeled target engine load of the engine and if, at a maximum combustion air ratio, the engine load inversion model with state feedback additionally lowers the modeled target exhaust gas temperature by reducing a modeled target engine load of the engine.

[0051] This makes it possible to reduce the actual exhaust gas temperature to a maximum.

[0052] In order to further increase the accuracy of the method, one embodiment of the method provides that the inner control loop comprises an exhaust gas temperature model for determining the actual exhaust gas temperature based on the updated actual engine operating conditions, which is connected downstream of the engine model and to which the modeled actual engine load adapted to the modeled target engine load and the modeled actual combustion air ratio adapted to the modeled target combustion air ratio are supplied by the engine model as input values ​​and which determines the modeled static actual exhaust gas temperature and the modeled dynamic actual exhaust gas temperature as output values.

[0053] By supplying the exhaust gas temperature model based on the updated actual engine operating conditions as well as the adjusted modeled actual engine load and the modeled actual combustion air ratio, the exhaust gas temperature model acts as a virtual temperature sensor for the exhaust gas temperature.

[0054] This eliminates the need for a real temperature sensor that measures the temperature of the exhaust gas and further increases the accuracy of the process.

[0055] In a further development of the engine model, it is provided that in order to determine the modeled static actual exhaust gas temperature, time-independent determinations are first carried out in which the influence of the modeled actual combustion air ratio is initially disregarded, and then the result of the time-independent determinations of the modeled static actual exhaust gas temperature is corrected with a correction factor dependent on the actual combustion air ratio.

[0056] This can further improve the result of the actual exhaust gas temperature.

[0057] The modeled actual temperature without enrichment influence is required as a feedback variable for the enrichment inversion model. By mapping the influence of enrichment in the inner control loop, the corresponding effect on the component temperature can be represented in the outer control loop, thus enabling a meaningful calculation of the control deviation.

[0058] In order to be able to calculate the modeled static ACTUAL exhaust gas temperature as accurately as possible, it is advantageous if the time-independent determination of the modeled static ACTUAL exhaust gas temperature of the exhaust gas temperature model comprises the following parallel or series pre-calculations, into which at least the ACTUAL engine load and the ACTUAL engine speed of the engine model are used as input values ​​and whose calculated parameters, in particular temperatures and / or correction factors, are used as input values ​​for determining the modeled static ACTUAL exhaust gas temperature: a. Determination of an offset temperature which is additionally dependent on the ACTUAL engine operating state; b. Determination of a base temperature which is additionally dependent on the positions of the variable inlet / exhaust valve timing of the variable valve control; c. Determination of an ignition angle and mixture correction factor which is additionally dependent on the ignition angle and mixture; and d.Determine an additional ambient / coolant temperature correction factor that depends on the ambient / coolant temperatures.

[0059] Furthermore, in one embodiment of the method, it is provided that the modeled static actual exhaust gas temperature, which is determined by the time-independent determination and corrected by the correction factor dependent on the actual combustion air ratio, is transferred as an input value to a downstream determination of the modeled dynamic actual exhaust gas temperature.

[0060] In a further development of the latter embodiment, it is provided that in order to determine the modeled dynamic actual exhaust gas temperature of the exhaust gas temperature model, the modeled actual exhaust gas flow rate is additionally transferred as an input value and the calculation comprises a post-oxidation model for determining the post-oxidation effects with a potentially temperature-increasing effect caused by the scavenging operating mode as well as a heat capacity model of the exhaust valves.

[0061] By calculating not only the dynamic component of the actual exhaust gas temperature of the exhaust gas temperature model, but also including post-oxidation effects with temperature-increasing effects as well as heat capacity models of the valves, the accuracy of the determined actual exhaust gas temperature value can be increased.

[0062] The exhaust gas temperature model determines the actual exhaust gas temperature. The inner control loop, specifically the exhaust gas temperature model, functions as a virtual exhaust gas temperature sensor. The final actual exhaust gas temperature corresponds to the dynamic actual exhaust gas temperature.

[0063] In order to determine an actual component temperature from the determined actual exhaust gas temperature, it proves to be advantageous if the outer control loop comprises a component temperature model to which the modeled actual exhaust gas temperature of the inner control loop is supplied as input values, in particular the modeled dynamic actual exhaust gas temperature of the exhaust gas temperature model, and a modeled actual exhaust gas mass flow, wherein the component temperature model approximates the heating / cooling behavior of the component by means of the modeled actual exhaust gas temperature via a low-pass filter (PT1) and the dynamics of the low-pass filter are dependent on the modeled actual exhaust gas mass flow, and wherein the modeled actual component temperature is determined as the output value.

[0064] In this case, the actual component temperature can be determined via the external control loop. By supplying the modeled actual exhaust gas temperature and an actual exhaust gas mass flow, the low-pass filter can determine whether the component is heating or cooling.

[0065] In order to close the control loop, in a further development of the latter embodiment, it is provided that the outer control loop comprises a closed-loop controller, in particular a proportional-integral controller, which comprises as input values ​​the modeled actual component temperature of the low-pass filter, the stored target component temperature, in particular the critical component temperature, or a control difference from the target component temperature subtracted by the actual component temperature, and the target exhaust gas temperature is determined as the output value.

[0066] In this case, the controller can regulate an increase or decrease of the actual component temperature by specifying a new target exhaust gas temperature.

[0067] In parallel, a pre-control component equal to the respective component temperature limit is applied to the control value of the closed-loop controller so that the downstream inversion models can perform a calculation based on the absolute temperature setpoints.

[0068] In order to further specify the target exhaust gas temperature to be passed on to the inner control loop, it is advantageous if the modeled target exhaust gas temperature determined by the closed-loop controller additionally receives a temperature offset determined by the post-oxidation model of the exhaust gas temperature model, by which post-oxidation effects with a temperature-increasing effect are calculated, and is passed on to the inner control loop as a corrected modeled target exhaust gas temperature.

[0069] In such cases, the closed-loop controller output is manipulated by a post-oxidation offset. The post-oxidation offset is a direct feedback value that can be fed back from the exhaust gas temperature model. This particularly covers post-oxidation effects during scavenging engine operation.

[0070] Finally, the object is achieved by an engine control system of a motor vehicle on which a method for exhaust gas temperature control with the aforementioned features can be carried out.

[0071] Further features, details and advantages of the invention emerge from the appended patent claims, from the drawings and the following description of a preferred embodiment of the method for exhaust gas temperature control.

[0072] The drawing shows: Figure 1 a schematic flow diagram of an embodiment of the method for exhaust gas temperature control;

[0073] Figure 2 A cascaded decoupled control system embedded in the engine control system with an inner control loop and an outer control loop.

[0074] Figure 1 shows a schematic flow diagram of an embodiment of the method for exhaust gas temperature control for a motor vehicle driven by an internal combustion engine with a cascaded, decoupled control 2 embedded in an engine control system of the motor vehicle.

[0075] The control 2 comprises an inner control loop 4 for controlling a modeled actual exhaust gas temperature of an exhaust gas of an internal combustion engine and an outer control loop 6 for controlling a modeled actual component temperature of a component absorbing or releasing exhaust heat.

[0076] In a first step 100, the reaching and exceeding of a modeled and / or real ACTUAL component temperature of the component via a maximum component temperature stored in the engine control system is detected by the outer control loop 6 or by a real temperature sensor. In a subsequent step 101, the detected modeled ACTUAL exhaust gas temperature is lowered by the inner control loop 4 to a modeled DESIRED exhaust gas temperature at which the modeled ACTUAL component temperature lies below the stored maximum component temperature, specifically by reducing a modeled ACTUAL engine load of the engine to a modeled DESIRED engine load of the engine and / or by increasing a modeled ACTUAL combustion air ratio to a modeled DESIRED combustion air ratio.In a subsequent step 102, the real ACTUAL engine load of the engine is set to the modeled DESIRED load of the engine and a real ACTUAL combustion air ratio of the engine is set to the modeled DESIRED combustion air ratio of the engine by the engine control unit by means of a processing component functionally assigned to the engine.

[0077] Referring to Figure 2, the inner control loop 4 for adapting the modeled engine load comprises an engine load inversion model 8 with state feedback, an enrichment inversion model 10 with state feedback for adapting the modeled combustion air ratio, and an engine model 12 in which modeled actual engine operating conditions, such as engine operating state, engine speed, torque demand, relative engine load, ignition angle, positions of the variable intake / exhaust valves, and / or ambient / coolant temperatures, are modeled. The engine load inversion model can receive the actual engine operating conditions of engine model 12 as input values, and the target component temperature and the current actual combustion air ratio from the outer control loop 6.

[0078] The enrichment inversion model 10 is supplied with a real actual engine speed and the relative actual engine load, the modeled desired exhaust gas temperature and the modeled actual exhaust gas temperature at a combustion air ratio of 1 as input value.

[0079] The engine load inversion model 8 provides the modeled target engine load as an output value, and the enrichment inversion model 10 provides the modeled target combustion air ratio. The modeled target engine load and the modeled target combustion air ratio are input to the engine model 12. The real engine operating conditions and the modeled actual engine operating conditions are then adapted to the input values, in particular to the target engine operating conditions determined therefrom, by actuating the associated actuators, such as the ignition and injection systems, the turbocharger wastegate actuator, and at least the adjusted modeled actual engine operating conditions are fed back to the engine load inversion model 8 and the enrichment inversion model 10 as an output value.

[0080] The inner control loop 4 of control 2 can be operated with different strategies.

[0081] With reference to Figure 1, the inner control loop 4 can be operated according to a so-called engine load strategy 10T, in which the modeled actual exhaust gas temperature is first reduced to a modeled target engine load by reducing the modeled actual engine load in a step 101'a, and then, if necessary, the modeled actual combustion air ratio is increased in a subsequent step 101'b. Furthermore, the inner control loop 4 can be operated according to an enrichment strategy 101, in which the modeled actual combustion air ratio is first increased in a step 101"'b, and then, in a step 101"'a, the actual engine load is reduced.

[0082] Furthermore, in a parallel strategy 101, the modeled actual engine load can be reduced in two parallel steps and, in parallel, the modeled actual combustion air ratio can be increased.

[0083] Returning to Figure 2, it can be seen that an exhaust gas temperature model 14 is provided downstream of the engine model 12 in the inner control loop 4. The exhaust gas temperature model 14 incorporates the modeled actual engine operating conditions, as well as the modeled actual engine load and the modeled actual combustion air ratio. The exhaust gas temperature model 14 functions as a virtual actual exhaust gas temperature sensor.

[0084] In the exhaust gas temperature model 14, time-independent determinations are initially carried out, in which the influence of the actual combustion air ratio is initially disregarded.

[0085] Subsequently, a modeled static actual exhaust gas temperature is determined from the time-independent measurements and, taking into account the modeled actual combustion air ratio, the modeled static actual exhaust gas temperature. This consists of an offset temperature, a base temperature, ignition angle and mixture correction factors, as well as ambient coolant temperature correction factors.

[0086] The resulting output value is then passed on to a downstream determination in which the modeled dynamic actual exhaust gas temperature is incorporated, taking into account post-oxidation effects through a post-oxidation model and a heat capacity model of the valves.

[0087] The output values ​​of the exhaust gas temperature model 14 are transferred to a low-pass filter 16 of the outer control loop 6, which receives the modeled actual exhaust gas temperature of the inner control loop 4 and a modeled actual exhaust gas mass flow as input values, and which determines the modeled actual component temperature as output value. This flows back to a closed-loop controller 18, in particular a proportional-integral controller (PI controller), which includes as input values ​​the modeled actual component temperature of the low-pass filter 16, the stored desired component temperature, in particular the critical component temperature, and / or a control difference between the desired / component temperature subtracted by the actual component temperature. The closed-loop controller 18 has the new desired exhaust gas temperature as output value, to which a pre-control component equal to the respective component temperature limit is applied.

[0088] A post-oxidation model 20 can be connected to the closed-loop controller 18. This model derives its values ​​from the calculation of the modeled dynamic ACTUAL exhaust gas temperature and corrects the TARGET exhaust gas temperature accordingly. The TARGET exhaust gas temperature then flows from the outer control loop 6 into the inner control loop 4, and the cascaded, decoupled control 2 is closed.

[0089] The features of the invention disclosed in the above description, in the claims and in the drawings can be essential both individually and in any combination in the realization of the invention in its various embodiments.

[0090] List of reference symbols

[0091] 2 Control 4 inner control loop

[0092] 6 outer control loop

[0093] 8 Engine load inversion model

[0094] 10 Enrichment inversion model

[0095] 12 Engine model 14 Exhaust temperature model

[0096] 16 Low-pass filter

[0097] 18 Closed-Loop Rules

[0098] 20 Post-Oxidation Model

Claims

P a t e n t a n s p r ü c h e 1. Method for exhaust gas temperature control for an internal combustion engine-powered motor vehicle with a cascaded, decoupled control system (2) embedded in an engine control unit of the motor vehicle, comprising an inner control loop (4) for controlling a modeled actual exhaust gas temperature of an exhaust gas of an internal combustion engine and an outer control loop (6) for controlling a modeled and real actual component temperature of a component that absorbs or releases heat through the exhaust gas, wherein at least when detecting that the modeled and / or real actual component temperature of the component is reached or exceeded via a maximum component temperature stored in the engine control unit, the outer control loop (6) or a real temperature sensor, a.a. the recorded modeled actual exhaust gas temperature is reduced by the inner control loop (4) to a modeled target exhaust gas temperature, at which the modeled actual component temperature is below the stored maximum component temperature, by reducing a modeled actual engine load of the engine to a modeled target engine load of the engine and / or by increasing a modeled actual combustion air ratio to a modeled target combustion air ratio; and b. a real actual engine load of the engine is adjusted to the modeled target engine load of the engine and a real actual combustion air ratio of the engine is adjusted to the modeled target combustion air ratio of the engine by the engine control unit by controlling the engine and / or a preparation component functionally assigned to the engine.

2. Method according to claim 1, characterized in that the inner control loop (4) for adjusting the modeled engine load of the engine comprises an engine load inversion model (8) with state feedback, that the inner control loop (4) for adjusting the modeled combustion air ratio comprises an enrichment inversion model (10) with state feedback and / or that the inner control loop (4) comprises an engine model (12) in which modeled actual values ​​are Engine operating conditions, in particular engine operating state, engine speed, torque demand, relative engine load, ignition angle, positions of the variable intake / exhaust valves and / or ambient / coolant temperatures, are modeled. The method according to claim 2 is characterized in that the modeled target exhaust gas temperature, the modeled actual engine operating conditions and the actual air-fuel ratio are supplied as input values ​​to the engine load inversion model (8) and the modeled target engine load is determined as output value, and that the enrichment inversion model (10) with state feedback receives the modeled target exhaust gas temperature and the modeled actual exhaust gas temperature at an actual air-fuel ratio of one.The modeled actual engine speed and the relative actual engine load are supplied as input values, and a modeled target air-fuel ratio is determined as an output value, and / or the modeled target engine load and the modeled target air-fuel ratio are supplied to the engine model (12) as input values, the real and modeled actual engine operating conditions are adapted to the input values, in particular from the target engine operating conditions determined therein, and the adapted modeled actual engine operating conditions are fed back as output values, at least to the engine load inversion model (8) and the enrichment inversion model (10). A method according to one of the preceding claims, characterized in that the inner control loop (4) can be operated according to an engine load strategy.in which the modeled actual exhaust gas temperature is first reduced by reducing the modeled actual engine load to a modeled target engine load, wherein the modeled actual air-fuel ratio is set to one regardless of the measured value. Method according to one of the preceding claims, characterized in that the inner control loop (4) can be operated according to an enrichment strategy in which the target exhaust gas temperature is first reduced by increasing the modeled actual air-fuel ratio, wherein the maximum enrichment of the modeled air-fuel ratio is unaffected by the modeled actual engine load. Method according to one of claims 3 to 5, characterized in that at a combustion air ratio of one, the engine load inversion model (8) with state feedback reduces the modeled target exhaust gas temperature solely by reducing the modeled target engine load of the engine, and that at a maximum combustion air ratio, the engine load inversion model (8) with state feedback additionally reduces the modeled target exhaust gas temperature by reducing a modeled target engine load of the engine.Method according to one of claims 2 to 6, characterized in that the inner control loop (4) comprises an exhaust gas temperature model (14) for determining the actual exhaust gas temperature based on the updated actual engine operating conditions, which is downstream of the engine model (12) and to which the modeled actual engine load adapted to the modeled target engine load and the modeled actual air-fuel ratio adapted to the modeled target air-fuel ratio are supplied as input values ​​by the engine model (12) and which determines the modeled static actual exhaust gas temperature and the modeled dynamic actual exhaust gas temperature as output values.Method according to claim 7, characterized in that, to determine the modeled static actual exhaust gas temperature, time-independent determinations are first carried out in which the influence of the modeled actual combustion air ratio is initially disregarded, and subsequently the result of the time-independent determinations of the modeled static actual exhaust gas temperature is corrected with a correction factor that depends on the actual combustion air ratio.Method according to claim 7 or 8, characterized in that the time-independent determination of the modeled static actual exhaust gas temperature of the exhaust gas temperature model (14) comprises the following parallel or series pre-calculations, into which at least the actual engine load and the actual engine speed of the engine model (12) are taken as input values ​​and whose respective calculated parameters, in particular temperatures and / or correction factors, are included as input values ​​in the determination of the modeled static actual exhaust gas temperature:. a. Determining an offset temperature that additionally depends on the current engine operating state; b. Determining a base temperature that additionally depends on the positions of the variable intake / exhaust valve timing of the variable valve timing; c. Determining an ignition angle and mixture correction factor that additionally depends on the ignition angle and mixture; and d. Determining an ambient / coolant temperature correction factor that additionally depends on the ambient / coolant temperatures. A method according to any one of claims 7 to 9, wherein the modeled static actual exhaust gas temperature, which is determined by the time-independent determination and corrected by the correction factor dependent on the current air-fuel ratio, is passed as an input value to a subsequent determination of the modeled dynamic actual exhaust gas temperature.The method according to claim 10, wherein, in order to determine the modeled dynamic actual exhaust gas temperature of the exhaust gas temperature model (14), the modeled actual exhaust gas flow rate is additionally passed as an input value and the calculation comprises a post-oxidation model (20) for determining the post-oxidation effects with temperature-increasing effect as well as a heat capacity model of the valves.A method according to one of the preceding claims, characterized in that the outer control loop (6) comprises a component temperature model to which the modeled actual exhaust gas temperature of the inner control loop (4) is supplied as input values, in particular the modeled dynamic actual exhaust gas temperature of the exhaust gas temperature model (14), and a modeled actual exhaust gas mass flow rate, wherein the component temperature model approximates the heating / cooling behavior of the component by the modeled actual exhaust gas temperature via a low-pass filter (PT1) (16) and the dynamics of the low-pass filter (16) depend on the modeled actual exhaust gas mass flow rate, and wherein the modeled actual component temperature is determined as the output value. The method according to claim 12, characterized in that the outer control loop (6) comprises a closed-loop controller (18), in particular a proportional-integral controller, which takes as input the modeled actual component temperature of the low-pass filter (16), the stored target component temperature, in particular the critical component temperature, or a control deviation of the target component temperature subtracted by the actual component temperature, and the target exhaust gas temperature is determined as the output. The method according to claim 13, characterized in that the modeled target exhaust gas temperature determined by the closed-loop controller (18) is additively adjusted by a temperature offset determined by the post-oxidation model (20) of the exhaust gas temperature model (14), which calculates post-oxidation effects with a temperature-increasing effect, and is passed to the inner control loop (4) as the corrected modeled target exhaust gas temperature.Engine control unit of a motor vehicle, on which a method for exhaust gas temperature control according to one of claims 1 to 14 can be implemented and in which a cascaded, decoupled control (2) is embedded, which comprises an inner control loop (4) for controlling a modeled actual exhaust gas temperature of an exhaust gas of an internal combustion engine and an outer control loop (6) for controlling a modeled and real actual component temperature of a component that absorbs or releases heat through the exhaust gas.

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