Diagnostic procedure for coupled exhaust gas turbochargers and diagnostic system

Abstract

The present invention relates to a diagnostic method for coupled exhaust gas turbochargers (10, 20) in an internal combustion engine (1), and to a diagnostic system for carrying out the diagnostic method according to the invention. According to the diagnostic method according to the invention, a first boost pressure is measured in a first charge air system (10a) of a first exhaust gas turbocharger (10) upstream of a first throttle valve (13), which leads to a first intake manifold (14) of a first cylinder bank (15), and a second boost pressure is measured in a second charge air system (20a) of a second exhaust gas turbocharger (20) upstream of a second throttle valve (23), which leads to a second intake manifold (24) of a second cylinder bank (25). Subsequently, a deviation between the first boost pressure and the second boost pressure is determined.Furthermore, the determined deviation is compared against a defined error threshold and an error message is issued if the deviation of the two boost pressures is greater than the error threshold.

Description

[0001] The present invention relates to a diagnostic method for coupled exhaust gas turbochargers in an internal combustion engine, as well as a diagnostic system for carrying out the diagnostic method according to the invention.

[0002] Exhaust gas turbochargers are known in the art as auxiliary units of the internal combustion engine that can be used to compress the air supplied to the combustion chamber to increase engine performance or efficiency. Part of the energy in the engine exhaust gas is used by a turbine and compressor to allow a larger volume of air to flow into the cylinder. The turbine extracts energy from the exhaust gas mass flow, which is then used in the compressor to increase the fresh air mass flow.

[0003] For example, embodiments of engines with multiple cylinder banks are known in which one exhaust gas turbocharger is used for each cylinder bank. Accordingly, a first compressor is provided, which compresses air into a first charge air system. The compressed air reaches a first intake manifold of the first cylinder bank via a first throttle valve as required. At the same time, a second exhaust gas turbocharger with a second compressor is provided, which compresses air into a second charge air system, from where it reaches the second intake manifold and the second cylinder bank via a second throttle valve. In some systems, the charge air systems and thus the exhaust gas turbochargers are coupled to one another via a pressure compensation element, so that pressure compensation of the boost pressures in the charge air systems can be achieved between the compressors and the throttle valves.In the context of the invention, we speak of coupled exhaust gas turbochargers when pressure equalization can be carried out between the charge air systems.

[0004] If one of the two turbochargers is damaged, either on the exhaust side or the fresh air side, for example, due to a leak or something similar, this turbocharger can no longer deliver its full power, causing the boost pressure in the corresponding cylinder bank to drop. In the case of minor damage, the coupling of the two charge air systems compensates for the power loss of one turbocharger by the other. Accordingly, the compressor of the functioning turbocharger runs at a higher power output to provide the same boost pressure in the charge air systems.

[0005] While this has the beneficial effect of preventing or at least reducing a loss of performance, it also poses a risk of overloading the undamaged turbocharger or its compressor, which can cause more serious damage. A defect in an exhaust turbocharger that prevents it from delivering the performance available during normal operation should therefore be detected by a diagnostic system to rule out major damage caused by sustained overload operation.

[0006] Patent document DE 10 2020 134 030 A1 discloses a diagnostic system for a two-bank combustion engine with an exhaust gas turbocharger, which can be used to monitor and control the function of a secondary air system. Pressure sensors are installed in the secondary air system for this purpose.

[0007] Patent document US 2007 / 0 163 258 A1 discloses an internal combustion engine with two intake ducts arranged in parallel. The intake air volumes in both intake ducts are measured and compared. This allows abnormalities in the air supply to be detected.

[0008] From patent document DE 196 15 033 A1, a system for detecting speed deviations between two exhaust gas turbochargers of an internal combustion engine consisting of two separate cylinder banks is known, in which a device determines the difference between the pressures prevailing in the two exhaust tracts of the two cylinder banks upstream of the exhaust gas turbines and signals a relevant speed deviation when a threshold value is exceeded.

[0009] The object of the present invention is, against the background of the prior art described above, to provide an alternative diagnostic method for coupled exhaust gas turbochargers in an internal combustion engine with at least two cylinder banks, as well as a diagnostic system for carrying out the diagnostic method according to the invention.

[0010] The object is achieved by the subject matter of the independent claims. Advantageous embodiments of the invention are disclosed in the subclaims. It should be noted at this point that advantageous embodiments of the diagnostic system according to the invention are also to be understood as disclosures of advantageous embodiments of the diagnostic method according to the invention, even if the wording of the description of the advantageous embodiment is directed to a system and not to a method. Thus, embodiments of the invention formulated as device features also disclose method features of a preferred embodiment of the method according to the invention. The same applies vice versa.

[0011] According to the diagnostic method according to the invention for coupled exhaust gas turbochargers in an internal combustion engine with at least two cylinder banks, a first boost pressure in a first charge air system of a first exhaust gas turbocharger upstream of a first throttle valve leading to a first intake manifold of a first cylinder bank and a second boost pressure in a second charge air system of a second exhaust gas turbocharger upstream of a second throttle valve leading to a second intake manifold of a second cylinder bank are measured, preferably independently of one another. A deviation between the first boost pressure and the second boost pressure is then determined. The deviation is determined by calculating the difference between the two boost pressures. These are measured, in particular by corresponding pressure sensors in the charge air systems, preferably continuously over time, so that corresponding curves are recorded.The deviation is always determined at a specific point in time, so that boost pressure values ​​from different points in time are not used to determine the deviation.

[0012] Furthermore, the determined deviation is compared against a defined error threshold, and an error message is issued if the deviation between the two boost pressures is greater than the error threshold. In other words, a difference between the boost pressures is first calculated, and the deviation between the first boost pressure and the second boost pressure is thus determined. If this difference is greater or smaller than a deviation value defined as the error threshold, a corresponding error is output. The error threshold thus describes the maximum permissible deviation between the first boost pressure and the second boost pressure.

[0013] Using the diagnostic procedure, it is therefore easy to diagnose if a fault occurs in one of the two exhaust turbochargers, either on the exhaust side or the fresh air side, and thus the compressor cannot generate the required pressure. Even if the reduced performance of the exhaust turbocharger can be temporarily compensated for by the other exhaust turbocharger in the event of a fault, the fault can be diagnosed and thus remedied with appropriate maintenance. Timely maintenance reduces the risk of overloading the functioning exhaust turbocharger.

[0014] In a preferred embodiment of the method according to the invention, the error threshold is determined as a function of a charge air mass flow, an engine speed, and / or a pressure ratio to be set by the throttle valves. In this way, the error threshold can be adapted to the corresponding operating point of the combustion engine, since different deviations between the first boost pressure and the second boost pressure can occur at different operating points, even without a defect in one of the exhaust gas turbochargers. This can improve the diagnosis.

[0015] Preferably, the boost pressures in the respective charge air system are measured in the direction of charge air flow between a pressure compensation element and the corresponding throttle valve. Thus, the boost pressure is taken just before the throttle valve. The signal used for this purpose, preferably detected by a sensor, can be the same signal used to control the throttle valve. This way, only one sensor needs to be used in the first charge air system and one sensor in the second charge air system, which reduces the number of parts and thus acquisition and manufacturing costs.

[0016] In an alternative embodiment, the boost pressures in the respective charge air system are measured in the direction of charge air flow upstream of a pressure compensation element, i.e., between the pressure compensation element and the corresponding compressor. This allows a compressor's power drop to be detected particularly quickly and precisely, thus enabling a particularly accurate boost pressure diagnosis.

[0017] Preferably, the boost pressures are measured continuously. Alternatively, the measurements are taken at specified intervals. A further preferred embodiment of the invention is one in which an error is only output when the deviation between the boost pressures over a certain period of time or over a predetermined number of measurements exceeds the error threshold. In this way, measurement errors in the sensor system can be ignored and misdiagnoses prevented.

[0018] The diagnostic system according to the invention is designed to carry out the method according to the invention. It has at least one first sensor in the first charge air system of the internal combustion engine, designed to measure the boost pressure in the first charge air system, and at least one second sensor in the second charge air system of the internal combustion engine, designed to measure the boost pressure in the second charge air system. Furthermore, an evaluation unit is provided, which is designed to determine a deviation in the boost pressures measured by the sensors and to compare it with an error threshold. The evaluation unit is further designed to output an error via an output unit if the deviation exceeds the error threshold.

[0019] The error threshold can be predefined, particularly for different operating points, and can be read from a correspondingly stored characteristic map, for example, or determined by the evaluation unit or another capable unit based on individual parameter values, such as a charge air mass flow, an engine speed, and / or a pressure ratio to be set by the throttle valves. A predefined error threshold is also conceivable.

[0020] The sensors are preferably arranged in their respective charge air systems either between a pressure compensation element and the respective throttle valve or between the pressure compensation element and the respective compressor. The sensors are preferably arranged at similar locations in the respective charge air systems, ensuring the comparability of the two sensor values ​​as accurately as possible. Thus, in one embodiment, the first sensor in the first charge air system is arranged between the pressure compensation element and the first throttle valve in the direction of charge air flow, and the second sensor in the second charge air system is preferably also arranged between the pressure compensation element and the second throttle valve.However, if in one embodiment the first sensor in the first charge air system is arranged between the pressure compensation element and the first compressor in the direction of charge air flow, the second sensor in the second charge air system is preferably also arranged between the pressure compensation element and the second compressor. Systems with multiple sensors for determining the boost pressure in the first charge air system and a boost pressure in the second charge air system are also conceivable.

[0021] Advantageous aspects and embodiments of the system and method according to the invention are explained in more detail below with reference to the accompanying figures. The figures show: Fig. 1 shows a schematic representation of an internal combustion engine 1 to which the method according to the invention can be applied. Fig. 2 shows a flow chart of the method according to the invention.

[0022] Fig. Figure 1 shows a schematic representation of an internal combustion engine 1 with a first exhaust turbocharger 10 and a second exhaust turbocharger 20, although exhaust sections of the exhaust turbochargers are not shown. The first exhaust turbocharger 10 is assigned to a first cylinder bank 15, and the second exhaust turbocharger 20 is assigned to a second cylinder bank 25.

[0023] The first exhaust gas turbocharger 10 has a first compressor 11 that compresses air into a first charge air system. Furthermore, the first exhaust gas turbocharger 10 has a first throttle valve 13 that delivers compressed air in the first charge air system, as needed, to a first intake manifold 14 connected to the individual cylinders of the first cylinder bank 15.

[0024] The second exhaust gas turbocharger 20 has a second compressor 21 that compresses air into a second charge air system. Furthermore, the second exhaust gas turbocharger 20 has a second throttle valve 23, which delivers compressed air in the second charge air system, as needed, to a second intake manifold 24, which is connected to the individual cylinders of the second cylinder bank 25.

[0025] Furthermore, a first pressure sensor 12 is provided in the first charge air system and a second pressure sensor 22 is provided in the second charge air system in order to detect the corresponding boost pressure in the charge air systems.

[0026] A pressure compensation element 30 in the form of a narrow fluidic connection is provided between the two charge air systems, which functions as a throttle. If a fault occurs, for example in the form of a leak in one of the two exhaust gas turbochargers, the other functioning exhaust gas turbocharger can compensate for the associated power losses to a certain extent; however, this requires operation at a higher load than in normal operation. The fault can be present in the exhaust section of a turbocharger 10, 20, so that the corresponding compressor 11, 21 cannot be supplied with the necessary power, or in the Fig. 1 shown fresh air part, so that compressed air escapes at one point and the boost pressure cannot be maintained. Accordingly

[0027] Fig.Figure 2 shows a flowchart of the method according to the invention. First, the boost pressures in the corresponding charge air systems are recorded by sensors 12, 22. The boost pressures are recorded continuously over time as boost pressure curves or measured at specified intervals. Subsequently, a deviation between the first boost pressure and the second boost pressure is determined. This is done by calculating the difference between the first and second boost pressures. The deviation is then compared against a maximum permissible deviation value, a so-called error threshold.

[0028] If the deviation between the first and second boost pressures exceeds the error threshold, an error is signaled to the driver via an output unit. This can be done, for example, via an acoustic and / or visual warning signal in the instrument cluster.

[0029] The error threshold is preferably determined based on a charge air mass flow, an engine speed, and / or a pressure ratio to be set by the throttle valves. This ensures an error threshold adapted to the engine's operating point.

[0030] Within the scope of the invention, it is also conceivable that an error is only output when the deviation exceeds the error threshold over a specified period of time or after a certain number of consecutive measurements. This allows, for example, individual measurement errors or similar errors to be identified in the diagnostic process and the probability of a misdiagnosis to be reduced.

[0031] Preferably, the measurement of the boost pressures in the charge air systems is carried out by means of the two pressure sensors 12, 22 shortly before the throttle valves 13, 23. Thus, the recorded pressure signals can also be used to control the throttle valves 13, 23 and there is no need to provide additional pressure sensors 12, 22 for the diagnostic procedure.

[0032] However, embodiments of the invention are also conceivable in which the pressure sensors 12, 22 are provided shortly after the compressors 11, 21 in order to be able to assess the performance of the compressors 11, 21 in the best possible way.

Claims

[1] Diagnostic method of coupled exhaust gas turbochargers (10, 20) in an internal combustion engine (1) with at least two cylinder banks (15, 25), comprising the following steps (A) measuring a first boost pressure in a first charge air system (10a) of a first exhaust gas turbocharger (10) upstream of a first throttle valve (13) which leads to a first intake manifold (14) of a first cylinder bank (15), (B) measuring a second boost pressure in a second charge air system (20a) of a second exhaust gas turbocharger (20) upstream of a second throttle valve (23) which leads to a second intake manifold (24) of a second cylinder bank (25), (C) Determining a deviation between the first boost pressure and the second boost pressure, (D) Comparison of the deviation between the boost pressures against an error threshold, (E) Output of an error message if the difference between the two boost pressures is greater than the error threshold. [2] Diagnostic method according to the preceding claim, wherein the error threshold is determined as a function of a charge air mass flow, an engine speed and / or a pressure ratio which the throttle valves (13, 23) are to set. [3] Diagnostic method according to one of the preceding claims, wherein the measurement of the charge pressures in the respective charge air system (10a, 20a) takes place in the flow direction of the charge air between a pressure compensation element (30) between the charge air systems (10a, 20a) and the corresponding throttle valve (13, 23). [4] Diagnostic method according to one of the preceding claims 1 or 2, wherein the measurement of the charge pressures in the respective charge air system (10a, 20a) takes place in the flow direction of the charge air upstream of a pressure compensation element (30) between the charge air systems (10a, 20a). [5] Diagnostic system designed to carry out the method according to one of the preceding claims, comprising at least one first pressure sensor (12) in the first charge air system (10a) of the internal combustion engine (1), designed to measure the boost pressure in the first charge air system (10a), at least one second pressure sensor (22) in the second charge air system (20a) of the internal combustion engine (1), designed to measure the boost pressure in the second charge air system (20a), and an evaluation unit which is designed to determine a deviation of the boost pressures measured by the sensors (12, 22) and to compare it with an error threshold, wherein the evaluation unit is further designed to output an error via an output unit if the deviation exceeds the error threshold.

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