Method for operating a motor vehicle with diagnostics of the function of a secondary air valve, motor vehicle

Abstract

A method is proposed for operating a motor vehicle (100) with an internal combustion engine (1) and a secondary air valve (2) for supplying a secondary air flow from a charge air duct (3) of the motor vehicle (100) into an exhaust duct (4) of the motor vehicle (100). For diagnosing the function of the secondary air valve (2), an air mass flow to the secondary air valve (2) is adjusted by means of an auxiliary valve (5) such that, in the event of a stuck open secondary air valve (2), a deviation of a lambda control value measurable by the motor vehicle (100) is generated. The auxiliary valve (5) is opened only to the extent necessary for the deviation to be measurable. Furthermore, a motor vehicle (100) is proposed.

Description

[0001] The present invention relates to a method for operating a motor vehicle with a diagnostic function of a secondary air valve. The present invention further relates to a motor vehicle.

[0002] Immediately after starting an internal combustion engine, the fuel mixture is adjusted with excess fuel to ensure smooth running. This results in some hydrocarbons leaving the engine unburned. The problem here is that in such a situation, the catalytic converter for exhaust gas purification typically has not yet reached its operating temperature and cannot remove the unburned hydrocarbons from the exhaust gas.

[0003] To reduce unburned hydrocarbons in the exhaust gas, modern vehicles introduce secondary air into the exhaust manifold, which is used for afterburning. This directly reduces the amount of unburned hydrocarbons. Furthermore, the afterburning process allows the catalytic converter to reach its operating temperature more quickly.

[0004] Secondary air is supplied as a secondary air flow via at least one secondary air valve. Monitoring the function of the secondary air valves is crucial for controlling the exhaust gas flow. This is typically done using the lambda value. However, the problem here is that the results can be influenced by the technical characteristics and operating conditions of the combustion engine.

[0005] From the publications DE 10 2019 213 787 A1 and JP 2008 - 31 968 A, a method for diagnosing a secondary air valve is known in which the lambda value is taken into account.

[0006] It is therefore an object of the present invention to provide a method for operating a motor vehicle with the diagnosis of the function of a secondary air valve and a motor vehicle which do not have the aforementioned disadvantages of the prior art, but offer a reliable diagnosis of the function of the secondary air valve.

[0007] This problem is solved by a method for operating a motor vehicle according to claim 1. This problem is further solved by a motor vehicle according to claim 8.

[0008] The inventive method for operating a motor vehicle comprises diagnosing the function of a secondary air valve. The motor vehicle has an internal combustion engine and the secondary air valve. The secondary air valve is designed to supply a secondary air flow from a charge air duct of the motor vehicle to an exhaust duct of the motor vehicle. An auxiliary valve is provided upstream of the secondary air valve in the direction of flow. For diagnosing the function of the secondary air valve, an air mass flow to the secondary air valve with the auxiliary valve is set, and a lambda control value is recorded.The auxiliary valve advantageously allows just enough secondary air to flow into the exhaust manifold when the secondary air valve is incorrectly open. This ensures that the lambda control value indicates an open secondary air valve, while simultaneously allowing only a small amount of secondary air to enter the exhaust manifold. This prevents the deviation from being measurable, thus avoiding unnecessarily rich fuel injection and preventing rough engine running. In particular, the auxiliary valve allows the secondary air flow through the secondary air valve to be regulated based on the exhaust back pressure in the exhaust manifold. When the vehicle is in motion, changing power demands on the combustion engine result in varying exhaust back pressure at the secondary air valve. When the driver accelerates, the exhaust back pressure increases, making it more difficult for secondary air to flow into the exhaust manifold.The secondary airflow can be adjusted accordingly by further opening the auxiliary valve.

[0009] Advantageous embodiments and further developments of the invention can be found in the dependent claims and in the description with reference to the drawings.

[0010] According to a preferred embodiment of the present invention, the diagnosis is performed during a second operating phase, wherein, during a first operating phase preceding the second operating phase, the secondary air valve and the auxiliary valve for heating a catalytic converter of the motor vehicle are open. This advantageously allows the exhaust system to first be switched to environmentally friendly operation. During the transition from the first to the second operating phase, the secondary air valve is actuated to close. If the secondary air valve is functioning correctly, it closes. However, it is also possible that the secondary air valve is defective and stuck open. Preferably, the secondary air flow is regulated by the auxiliary valve during the first operating phase.This ensures that the exhaust back pressure does not exceed the pressure of the secondary air and that sufficient secondary air is supplied to the exhaust duct.

[0011] Preferably, the system provides that the auxiliary valve is closed during a third operating phase, which in particular follows the second operating phase. During this operating phase, a lambda control reference value is determined. For diagnostic purposes, the lambda control value is normalized using the lambda control reference value. This allows deviations, which may be due to engine or fuel conditions, for example, to be taken into account, thus improving the diagnostic process.

[0012] According to a further preferred embodiment of the present invention, the air-fuel ratio of the internal combustion engine is controlled based on a lambda value measured in the exhaust manifold. The lambda control value is a function of a control signal, which serves to regulate the air-fuel ratio. The control signal is determined by the difference between the measured lambda value and a target lambda value. Diagnosis based on the lambda control value determined in this way is significantly more informative than diagnosis based solely on the lambda value measured in the exhaust manifold. If the lambda value deviates from the target value, the air-fuel ratio is readjusted, so that if there is significantly too much secondary air, the internal combustion engine runs very rich, but the lambda value is approximately 1, and the excess secondary air is hardly detectable.

[0013] For this purpose, it is preferably provided that during the second operating phase, the lambda control value, preferably normalized, is integrated over time for diagnostic purposes. This makes the diagnosis significantly more informative and accurate. A stuck-open secondary air valve can thus be detected very reliably.

[0014] According to a further preferred embodiment of the present invention, the air mass flow is continuously adjusted by the auxiliary valve during the second operating phase, depending on the exhaust back pressure. This advantageously makes it possible to take into account the purge pressure ratio, i.e., the ratio between exhaust back pressure and secondary air pressure when the secondary air valve is stuck open, and to reliably detect a fault in the secondary air valve.

[0015] According to a further preferred embodiment of the present invention, the air mass flow is generated by a turbocharger of the motor vehicle, in particular by an electrically assisted or electrically driven turbocharger. This advantageously makes it possible to generate the secondary air flow or the air mass flow without having to install additional devices for generating the air flow.

[0016] A particularly preferred embodiment of the present invention comprises an internal combustion engine with one cylinder bank and another cylinder bank. The exhaust port is assigned to the cylinder bank, meaning that the exhaust gas from the cylinder bank is discharged via the exhaust port. The vehicle has a further secondary air valve for supplying a further secondary air flow from the charge air duct into a further exhaust port of the vehicle. This further exhaust port receives exhaust gas from the second cylinder bank and directs it into the exhaust port. For diagnostic purposes, a further air mass flow to the further secondary air valve is set by means of the auxiliary valve, analogous to the secondary air valve. The further exhaust port preferably opens into the exhaust port. In other words, the exhaust gas from the cylinder bank is discharged via the exhaust port.The exhaust gas from the other cylinder bank is routed via the secondary exhaust port, which leads into the main exhaust port. The secondary air valve is designed to supply the secondary airflow to the main exhaust port, preferably before the secondary exhaust port joins it. The secondary air valve is designed to supply the secondary airflow to the main exhaust port. The air mass flow to the secondary air valve and the additional air mass flow to the secondary air valve are regulated by the auxiliary valve.

[0017] Another object of the present invention for solving the problem formulated at the outset is a motor vehicle, wherein the motor vehicle is configured to carry out a method according to the invention.

[0018] According to a preferred embodiment of the present invention, the secondary air valve is connected to one cylinder bank, and a further secondary air valve is connected to another cylinder bank of the motor vehicle. The additional valve regulates a further air mass flow to the further secondary air valve. This occurs analogously to the regulation of the air mass flow to the secondary air valve and enables the diagnosis of the further secondary air valve.

[0019] According to a further preferred embodiment of the present invention, the charge air duct is arranged to branch off from a turbocharger. The turbocharger is, in particular, an electrically assisted or electrically driven turbocharger. This advantageously makes it possible to generate the secondary airflow or the further secondary airflow without having to provide a separate device for this purpose.

[0020] All details, features and advantages previously disclosed in connection with the motor vehicle according to the invention also relate to the method according to the invention.

[0021] Further details, features, and advantages of the invention will become apparent from the drawings and from the following description of preferred embodiments with reference to the drawings. The drawings merely illustrate exemplary embodiments of the invention, which do not limit the inventive concept. Fig. Figure 1 schematically illustrates a detail of a motor vehicle according to an exemplary embodiment of the present invention. Fig. Figure 2 schematically illustrates a motor vehicle according to an exemplary embodiment of the present invention.

[0022] Fig. Figure 1 schematically illustrates a detail of a motor vehicle 100 (see Fig.2) according to an exemplary embodiment of the present invention.

[0023] The diagram shows an internal combustion engine 1 with cylinder bank 6 and another cylinder bank 6.1. Combustion air is supplied to cylinder banks 6 and 6.1 via a charge air duct 3, supplied by a turbocharger 9. The pressure in the charge air duct 3 is monitored by a pressure sensor 10. An intercooler 11 is located upstream of the pressure sensor 10. The exhaust gas from cylinder bank 6 is discharged via an exhaust duct 4. The exhaust gas from the other cylinder bank 6.1 is discharged via a further exhaust duct 4.1, which leads into the exhaust duct 4.

[0024] When the combustion engine 1 is started, the ratio of combustion air to supplied fuel is initially adjusted so that more fuel is supplied than is burned in the combustion engine 1. To reduce the emission of unburned hydrocarbons, so-called secondary air is added to the exhaust gas. For this purpose, a secondary air flow is drawn from the charge air duct 3 during a first operating phase. This flows from the charge air duct 3 via an air supply line 7 to a secondary air valve 2. The secondary air flow can be regulated by an additional valve 5 located upstream of the secondary air valve 2. Furthermore, another secondary air flow is drawn from the charge air duct 3. This flows from the charge air duct 3 via another air supply line 7.1 to a further secondary air valve 2.1. The additional valve 5, which is also located upstream of the further secondary air valve 2.1, can regulate this further secondary air flow.The secondary air flow is directed from secondary air valve 2 into exhaust duct 4. A further secondary air flow is directed from secondary air valve 2.1 into exhaust duct 4.1. The supply of secondary air results in afterburning in exhaust duct 4, which contributes to a reduction of unburned hydrocarbons and to the rapid heating of a catalyst (not shown). After the initial operating phase, secondary air valves 2 and 2.1 are closed.

[0025] To test whether the secondary air valves 2 and 2.1 are actually closed, the auxiliary valve 5 is opened just enough to generate a measurable deviation in a lambda control value if a secondary air valve 2 or another secondary air valve 2.1 is stuck open. However, the auxiliary valve 5 is only opened to the point where the deviation is just measurable in the case of a stuck-open secondary air valve 2 or 2.1, preventing an unnecessarily large amount of secondary air from entering the exhaust manifold. This prevents the combustion engine 1 from running very rich due to an excessively high proportion of secondary air.

[0026] The lambda control value is a function of a control signal used to regulate the air-fuel ratio. This control signal is determined by the difference between a measured lambda value in exhaust gas channel 4 and a target lambda value. The lambda value is determined by a lambda sensor (not shown). The target lambda value is typically 1 or slightly higher. If the measured lambda value deviates from the target lambda value, the air-fuel ratio is adjusted. The control signal serves as the basis for determining the lambda control value. In particular, the control signal can be the lambda control value itself.

[0027] To account for vehicle- or situation-specific variations in the lambda control value that are not caused by a defective secondary air valve 2, 2.1, it is provided that in a third operating phase the auxiliary valve 5 is closed and a lambda control reference value is determined. This reference value, like the lambda control value, is a function of the controller signal and serves to normalize the lambda control value. Reference symbol list 1 Internal combustion engine 2 Secondary air valve 2.1 Additional secondary air valve 3 Charge air duct 3.1 Additional charge air duct 4 Exhaust channel 4.1 Additional exhaust duct 5 Additional valve 6-cylinder bank 6.1 further cylinder bank 7. Air supply line 7.1 Additional supply air duct 9 turbochargers 10 additional pressure sensors 11 Intercoolers 100 motor vehicles

Claims

[1] Method for operating a motor vehicle (100) with an internal combustion engine (1) and a secondary air valve (2) for supplying a secondary air flow from a charge air duct (3) of the motor vehicle (100) into an exhaust duct (4) of the motor vehicle (100), wherein, for a diagnosis of the function of the secondary air valve (2), an air mass flow to the secondary air valve (2) is adjusted by means of an auxiliary valve (5) such that, in the event of a stuck open secondary air valve (2), a deviation of a lambda control value measurable by the motor vehicle (100) is generated, wherein the auxiliary valve (5) is opened only to the extent that the deviation is measurable. [2] Method according to claim 1, characterized by, that the diagnosis is carried out during a second operating phase, wherein during a first operating phase preceding this first operating phase the secondary air valve (2) and the auxiliary valve (5) for heating a catalyst of the motor vehicle (100) are open, wherein during the transition from the first operating phase to the second operating phase the secondary air valve (2) is actuated to close, wherein preferably the secondary air flow during the first operating phase is regulated by the auxiliary valve (5). [3] Method according to claim 2, characterized by , that during a third operating phase, which preferably follows the second operating phase, the auxiliary valve (5) is closed, whereby a lambda control reference value is determined, wherein the lambda control value is normalized using the lambda control reference value for diagnostic purposes. [4] Method according to any one of claims 1 to 3, characterized by, that the air-fuel ratio of the internal combustion engine (1) is controlled on the basis of a lambda value measured in the exhaust channel (4), wherein the lambda control value is a function of a controller signal, wherein the controller signal serves to control the air-fuel ratio, wherein the controller signal is determined by a difference between the measured lambda value and a target lambda value. [5] Method according to claim 4, characterized by , that during the second operating phase, the lambda control value, preferably normalized, is integrated over time for diagnostic purposes. [6] Method according to any one of claims 2 to 5, characterized by , that during the second operating phase the air mass flow is continuously adjusted by the additional valve (5) depending on the exhaust back pressure. [7] Method according to any one of the preceding claims, characterized by, that the mass airflow is generated by a turbocharger (9) of the motor vehicle, in particular by an electrically assisted or electrically driven turbocharger (9). [8] Motor vehicle (100), wherein the motor vehicle (100) is configured to perform a method according to any of the preceding claims. [9] Motor vehicle (100) according to claim 8, characterized by , that the secondary air valve (2) is connected to a cylinder bank (6), wherein a further secondary air valve (2.1) is connected to a further cylinder bank (6.1) of the motor vehicle (100), wherein the auxiliary valve (5) regulates a further mass air flow to the further secondary air valve (2.1). [10] Motor vehicle (100) according to one of claims 8 to 9, characterized by , that the charge air duct (3) is arranged leading away from a turbocharger (9).

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