Methods for diagnosing a secondary air system of an internal combustion engine and internal combustion engine

Abstract

Method for diagnosing a secondary air system (32) of an internal combustion engine (20), which introduces secondary air into an exhaust system (28) of the internal combustion engine (30), which reacts exothermically with combustible exhaust gas components in a reaction zone of the exhaust system (28), in which secondary air is supplied through the secondary air system (32) by means of a secondary air pump (34), characterized in that the secondary air pump (34) is operated in a speed-controlled manner, that a measure for the supplied secondary air is formed from at least one control variable of the secondary air pump (34), that the measure for the supplied secondary air is compared with at least one threshold value, and that a diagnostic signal is provided depending on the result of the comparison, wherein the measure comprises a control current value of the controlled secondary air pump.

Description

The invention relates to a method for diagnosing a secondary air system of an internal combustion engine with the features according to the preamble of claim 1. Furthermore, the invention relates to an internal combustion engine with the features according to the preamble of claim 10. For internal combustion engines, it is necessary to check or diagnose the proper operation of individual components so that any faults that occur can be identified, their circumstances documented, and, if necessary, corrective action can be taken. In one class of internal combustion engines, so-called secondary air systems with secondary air pumps are used, which supply air, particularly from a fresh gas system, to the exhaust system. The proper functioning of the secondary air system, especially the secondary air pump, must also be diagnosed. Document DE 10 2004 016 418 A1 discloses a fault diagnosis device for a secondary air supply. A malfunction is detected based on the pressure and pressure pulsations measured by a pressure sensor in a secondary air supply path. The presence or absence of pressure pulsations is determined by comparison with a threshold value, which varies depending on the pressure. Document DE 10 2004 001 330 A1 describes a method for diagnosing the secondary air system of an internal combustion engine. A measure of the secondary air input is determined and evaluated based on the thermal behavior in the thermoreactor. A diagnostic signal is then generated based on a comparison with a threshold value. Document DE 43 09 854 A1 describes a method and a device for controlling the supply of secondary air to the exhaust gas of an internal combustion engine and a method for diagnosing this device. The secondary air pump can be operated in stages. For diagnostic purposes, a rich mixture is supplied to the operating-temperature internal combustion engine. The mixture composition is measured using an exhaust gas probe. If the secondary air injection is functioning correctly, a lean mixture is detected. The absence of the lean signal is interpreted as a fault in the secondary air injection system, and a corresponding error message is stored or displayed. Document DE 102 05 966 ​​A1 relates to a method and a device for monitoring the functionality of a secondary air system, in which the pump current, an operating characteristic, of a pulsed secondary air pump is evaluated. A fault in the secondary air system is inferred if the pump current signal lies outside a predefinable interval. From DE 10 2004 006 876 A1 a method for operating an electrically driven secondary air pump is known. The object of the present invention is to provide a method for diagnosing a secondary air system, in particular a secondary air pump of a secondary air system, which does not require gas sensors, for example pressure sensors or exhaust gas probes. This problem is solved according to the invention by a method for diagnosing a secondary air system of an internal combustion engine with the features according to claim 1. Advantageous embodiments of the invention are characterized in the dependent claims. In the inventive method for diagnosing a secondary air system of an internal combustion engine, the secondary air system introduces secondary air into the exhaust system of the internal combustion engine. The secondary air reacts exothermically with combustible exhaust gas components in a reaction zone of the exhaust system. The secondary air is pumped through the secondary air system by means of a secondary air pump. According to the invention, the secondary air pump is operated with speed control, particularly during the pumping of the secondary air. A measure of the delivered secondary air is derived from at least one control variable of the secondary air pump, and in particular, also evaluated. The measure of the delivered secondary air is compared with at least one threshold value. Depending on the result of the comparison, a diagnostic signal is provided or generated. The secondary air pump used according to the invention is, in particular, an electric, preferably electrically commutated, secondary air pump. In other words, the secondary air pump can have an electric drive. The secondary air pump is speed-controlled. It features, in particular, current measurement of its control. For example, the secondary air pump comprises a brushless, electronically commutated DC motor (BLDC). In the method according to the invention, the measured value and the threshold value are compared in a control unit and / or the diagnostic signal is provided by the control unit. The control unit can also be referred to as a motor control unit or a motor control computer. Alternatively, one or more process steps can be carried out in a control unit of the secondary air pump, a microcontroller. The combustible exhaust gas components can be solid components or solid particles, in particular soot or soot particles. According to the invention, the fact that a variable-speed secondary air pump is operated in a controlled manner is used to diagnose its function from the behavior or changes in the control variables of the secondary air pump. A fault in the secondary air supply can be diagnosed. Blockages lead to increased back pressure, and leaks lead to lower back pressure against which the secondary air pump operates. If a fault occurs in the secondary air supply, a change in the counter-torque at the secondary air pump, particularly at its electric motor, results. In other words, the changed counter-torque affects the speed and / or the control variables, the manipulated variables, and / or the reference variables for the secondary air pump. In particular, the electrical current and / or the control of the electric motor can be affected.Therefore, a deviation from a stored model, a reference value, or a threshold value may occur. Specifically, for example, the control signal of the pump can be evaluated to assess the functionality of the secondary air system, in particular by additionally evaluating a current signal (and / or a signal derived from it). This means that if the control variable is at its limit or deviates from an expected value, especially if the current also deviates from a model or threshold value, the system can be diagnosed as faulty. In addition, the pressure signal in the secondary air line can also be linked, for example. This means that if a fault is detected via the pressure sensor and, according to the invention, a deviation occurs in a control and / or regulation signal of the secondary air pump, the secondary air pump is directly identified as a faulty part. The comparison performed according to the invention can, in particular, be carried out with both a lower / first threshold and an upper / second threshold, wherein the lower threshold is lower than the upper threshold. A diagnostic signal is then provided if the measurement is below the lower threshold or above the upper threshold. In other words, the diagnostic method can be further developed such that, by comparison, it is verified that the measurement of the delivered secondary air lies within a specified interval. The secondary air system can be a line leading to the exhaust system of an internal combustion engine. Alternatively, the secondary air system line can branch off from the fresh air intake system of the internal combustion engine. The design of the secondary air system can vary depending on the engine. For example, it can consist of a system of lines, particularly several branched lines. The branches can be located downstream of the secondary air pump in the secondary air system. Individual lines can each have valves, especially shut-off valves. In the diagnostic method according to the invention, secondary air is preferably introduced into the exhaust system upstream or upstream, and in particular directly upstream or upstream, of an exhaust aftertreatment device. The exhaust aftertreatment device can be located in the reaction zone. Advantageously, the exhaust aftertreatment device can be heated by means of secondary air and combustible exhaust gas components. The exhaust aftertreatment device can be a particulate filter to which air is supplied for regeneration, and a specific temperature must be maintained. In the particularly important case where the internal combustion engine is a spark-ignition engine, the exhaust aftertreatment device can be a gasoline particulate filter. In one group of embodiments of the method according to the invention, the internal combustion engine is operated in a Otto cycle or an Otto-Miller cycle, in particular with external ignition by spark plugs. The internal combustion engine can be or be turbocharged, for example by means of a turbocharger or an electrically driven compressor. The internal combustion engine is preferably operated stoichiometrically. In advantageous embodiments of the method according to the invention, a control profile and / or a torque profile and / or a current profile, in particular a drive current profile, of the secondary air pump is evaluated to determine the measure for the delivered secondary air. In a specific embodiment of these processes, a gradient or a gradient profile, in particular of the aforementioned profiles, can be determined in the evaluation. In alternative embodiments of the method according to the invention, a rotational speed and / or a change in rotational speed of the secondary air pump is determined to form the measure. A particular advantage of the method according to the invention is that no additional sensors beyond those used for controlling and / or regulating the secondary air pump are required. In further developments of the method according to the invention, the provided diagnostic signal can be used more extensively: Based on the diagnostic signal, an error entry can be written to an error memory, in particular a control unit. Additionally or alternatively, depending on the diagnostic signal, a signal perceptible to a human sense can be output to an output unit. The perceptible signal can be visual, acoustic, or haptic. For example, the output unit can be a warning lamp, a screen, or a loudspeaker. Again, additionally or alternatively, depending on the diagnostic signal, an intervention can be made in at least one operating control parameter or operating regulation parameter of the internal combustion engine, in particular by means of the control unit.For example, the operating point of the internal combustion engine can be changed to mitigate the effects of any fault that may be detected. In some embodiments of the method according to the invention, it may be provided that the diagnostic signal is evaluated remotely from the internal combustion engine. For this purpose, the diagnostic signal can be transmitted from the control unit of the internal combustion engine to a computer separate from the internal combustion engine, for example in a workshop. Also related to the inventive concept is a control unit for an internal combustion engine, wherein the control unit comprises at least a computer and a storage element. In the control unit according to the invention, a program is stored in the storage element which, when at least partially executed in the computer, performs the steps of the method for diagnosing a secondary air system of the internal combustion engine with features or combinations of features as described in this illustration. An internal combustion engine according to the invention, in particular a reciprocating internal combustion engine, comprising an exhaust system, a secondary air system and a control unit, includes a control unit according to the invention. The internal combustion engine is particularly preferably a spark-ignition engine, wherein the exhaust system includes a gasoline particulate filter, in particular as an exhaust aftertreatment device. The internal combustion engine according to the invention can be an internal combustion engine powered by gasoline as fuel. Alternatively, the internal combustion engine according to the invention can be an internal combustion engine powered by gas, preferably methane or CNG, as fuel. In a group of embodiments, the internal combustion engine is bivalent, in particular, capable of being operated alternately with gasoline and gas as fuels. Preferably, the internal combustion engine according to the invention is part of a drive unit of a vehicle, in particular a trackless land vehicle. Further advantages and advantageous embodiments and developments of the invention are presented in the following description with reference to the figures. Specifically, Fig. 1 shows a flowchart of a preferred embodiment of the method according to the invention, and Fig. 2 shows a schematic representation of an internal combustion engine according to the invention, whose secondary air system can be diagnosed in the method according to the invention by means of the control unit. Figure 1 shows a flowchart of a preferred embodiment of the inventive method for diagnosing a secondary air system of an internal combustion engine with a control unit. The internal combustion engine is preferably a spark-ignition engine. A variable-speed secondary air pump is used, by means of which secondary air is supplied through the secondary air system to introduce the secondary air into a reaction zone in the exhaust system of the internal combustion engine, preferably upstream of a gasoline particulate filter of the internal combustion engine. There, the secondary air reacts exothermically with combustible exhaust gas components, which are collected, in particular, in an exhaust aftertreatment device, for example, a filter. In step 10 of the preferred embodiment of the method according to the invention, secondary air is controlled and supplied to the exhaust system, in particular to the gasoline particulate filter, by means of the operated secondary air pump. This supply preferably takes place while the internal combustion engine is running. In step 12, a measure of the supplied secondary air is calculated from at least one control variable of the secondary air pump. Specifically, this measure is the actual control current value of the controlled secondary air pump. In step 14, the calculated measure is compared with at least one threshold value, specifically with a control current reference value or a control current extreme value.If the back pressure deviates from the expected value, the measured value will deviate from the threshold. Specifically, a deviation of the control current from the control current extreme value, for example, an exceedance, can be detected. This result is interpreted as an indication of a fault, specifically a blockage: In step 16, a diagnostic signal is provided or generated depending on the result of the comparison, specifically whether the threshold has been exceeded. Subsequently, in step 18, the diagnostic signal is processed: The diagnostic signal can serve as a trigger to write an error entry to a fault memory of the control unit. The error entry can, in particular, include a collection of data from a selection of operating parameters of the internal combustion engine.Furthermore, the operating state of the internal combustion engine can be changed based on the diagnostic signal in order to mitigate or preferably compensate for the effects of a potentially faulty secondary air supply. Figure 2 schematically depicts an internal combustion engine 20 according to the invention, the secondary air system 32 of which can be diagnosed using the control unit 42 in the inventive method. Preferably, it is an externally ignited internal combustion engine. The internal combustion engine 20 has an engine block 22 with, by way of example, four combustion chambers, in particular cylinders, graphically indicated in Figure 2 by the circles on the engine block 22. Each of the combustion chambers is assigned an ignition spark device 24, for example, a spark plug. Preferably, a fuel, specifically gasoline, is injected directly into the combustion chambers of the internal combustion engine. Alternatively, it can be a gas-powered internal combustion engine. Gas injection preferably takes place at several points in an intake manifold (MPI) upstream of the combustion chambers. Fresh gas, in particular air, is supplied to the engine block 22 of the internal combustion engine 20 according to the invention via a fresh gas system 26. Exhaust gas is discharged from the combustion chambers of the engine block 22 via an exhaust system 28. The exhaust system includes an exhaust aftertreatment device 30, preferably a gasoline particulate filter. Although not shown in Fig. 2, the fresh gas system 26 and the exhaust system 28 can include further components: For example, one or more charging units, such as turbochargers or electrically driven compressors, can be present. Furthermore, the exhaust system can include additional exhaust aftertreatment devices, for example, a three-way catalytic converter. The fresh gas system 26 and / or the exhaust system 28 can be multi-flow, i.e., have branching points and / or outlet points.Finally, the internal combustion engine may also include one or more exhaust gas recirculation (EGR) lines, in particular a high-pressure exhaust gas recirculation and / or a low-pressure exhaust gas recirculation. Figure 2 shows an embodiment of the internal combustion engine according to the invention, in which the fresh gas system 26 is fluidically connected to the exhaust system 28 by means of a secondary air system 32, specifically a secondary air line. To supply secondary air through the secondary air system 32, the secondary air system 32 includes a secondary air pump whose impeller moves fresh gas, in particular air, towards the exhaust system 28. The secondary air pump is driven at a variable speed by an electric motor 36. The electric motor 36 can be controlled and / or regulated by a microcontroller 38. In particular, the electric motor 36 is controlled at a variable speed. In the preferred context of an externally ignited internal combustion engine with spark ignition and Otto combustion process and Otto particulate filter, the Otto particulate filter loaded with soot particles can be regenerated by supplying air to the Otto particulate filter via the secondary air system 32 for combustion of the soot particles, provided that a sufficiently high temperature prevails at the Otto particulate filter. The secondary air supply can be interrupted by means of a shut-off valve 40. The shut-off valve can be designed simply in that it only needs to be able to assume a fully open and a fully closed state digitally. The mass flow rate can be varied by means of the controlled secondary air pump, since the secondary air pump is speed-variable according to the invention. The internal combustion engine 20 according to the invention comprises a control unit 42 according to the invention, including a computer and a memory element. A program is stored in the memory element which, when at least partially executed in the computer, performs the steps of the method for diagnosing a secondary air system of the internal combustion engine, as explained in more detail above with reference to Fig. 1. The control unit 42 is in signal and / or functional communication with the secondary air pump 34, specifically with its microcontroller 38, with the shut-off valve 40, and with actuators of the engine block 22, for example, the ignition spark devices 24. The diagnostic signal can be provided in the control unit 42 and / or in the microcontroller 38 and / or the measure of the secondary air supplied can be determined. Part of the storage element of the control unit 42 can be used for the fault memory according to the invention. In this embodiment, the control unit 42 has an interface for reading the fault memory. Not shown in Fig. 2, the control unit 42 can also be connected to an output unit, for example a display element, via signal and / or functional communication, so that a signal perceptible to a human, for example a light signal from a light-generating element, can be displayed in response to the diagnostic signal. Reference symbol list 10 Step of controlled secondary air supply 12 Step of determining a measurement 14 Step of comparing with a threshold value 16 Step of outputting a diagnostic signal 18 Step of processing the diagnostic signal 20 Internal combustion engine 22 Engine block 24 Ignition spark device 26 Fresh gas system 28 Exhaust system 30 Exhaust aftertreatment device 32 Secondary air system 34 Secondary air pump 36 Electric motor 38 Microcontroller 40 Shut-off valve 42 Control unit

Claims

Method for diagnosing a secondary air system (32) of an internal combustion engine (20), which introduces secondary air into an exhaust system (28) of the internal combustion engine (30), which reacts exothermically with combustible exhaust gas components in a reaction zone of the exhaust system (28), in which secondary air is supplied through the secondary air system (32) by means of a secondary air pump (34), characterized in that the secondary air pump (34) is operated in a speed-controlled manner, that a measure for the supplied secondary air is formed from at least one control variable of the secondary air pump (34), that the measure for the supplied secondary air is compared with at least one threshold value, and that a diagnostic signal is provided depending on the result of the comparison, wherein the measure comprises a control current value of the controlled secondary air pump. Method for diagnosing a secondary air system (32) according to claim 1, characterized in that the measure and the threshold value are compared in a control unit (42) and / or that the diagnostic signal is provided by the control unit (42). Method for diagnosing a secondary air system (32) according to claim 1 or 2, characterized in that the secondary air is introduced into the exhaust system (28) upstream of an exhaust aftertreatment device (30). Method for diagnosing a secondary air system (32) according to one of the preceding claims, characterized in that the internal combustion engine (20) is operated in an Otto process or an Otto-Miller process. Method for diagnosing a secondary air system (32) according to one of the preceding claims, characterized in that a control profile and / or a torque profile and / or a current profile of the secondary air pump is evaluated to form the measure. Method for diagnosing a secondary air system (32) according to claim 5, characterized in that a gradient or gradient profile is determined in the evaluation. Method for diagnosing a secondary air system (32) according to one of the preceding claims 1 to 4, characterized in that a rotational speed and / or a change in rotational speed of the secondary air pump (34) is determined to form the measure. Method for diagnosing a secondary air system (32) according to one of the preceding claims, characterized in that, based on the diagnostic signal, an error entry is written into an error memory and / or, depending on the diagnostic signal, an output of a signal perceptible to a human is made on an output unit and / or, depending on the diagnostic signal, an actuating intervention is made on at least one operating control parameter or operating regulation parameter of the internal combustion engine (20). Control unit (42) of an internal combustion engine (20), wherein the control unit (42) comprises at least one computer and a storage element, characterized in that a program is stored in the storage element which, when executed at least partially in the computer, performs the steps of the method for diagnosing a secondary air system (32) of the internal combustion engine (20) according to one of the preceding claims. Internal combustion engine (20) with an exhaust system (28), a secondary air system (32) and a control unit (42), characterized in that the control unit (42) is a control unit (42) according to claim 9, that the internal combustion engine (20) is a spark-ignition internal combustion engine (20) and that the exhaust system (28) has a gasoline particulate filter.

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