Method for detecting coking in the intake tract of an internal combustion engine

Abstract

Method for detecting a fault, in particular coking, in the intake tract of an internal combustion engine with direct fuel injection, throttle valve and variable intake valve lift control, comprising the steps: a) Performing an initial quantity deviation test, by which an initial air-fuel ratio value (w1) is determined from a lambda value (λ) measured during the initial quantity deviation test real, 1 ) and a desired lambda value (λ soll, 1 ) the fuel combustion in the combustion chambers of the internal combustion engine, whereby in the first quantity deviation test a load control is carried out by means of the variable intake valve lift control; b) Performing a second quantity deviation test to determine a second air-fuel ratio value (w2) from a lambda value (λ) measured during the second quantity deviation test real, 2 ) and a desired lambda value (λ soll, 2) the fuel combustion in the combustion chambers of the internal combustion engine, whereby in the second quantity deviation test a load control is carried out by means of the throttle valve; c) Determining a comparison result from the first air ratio value (w1) and the second air ratio value (w2), whereby the presence of a fault in the intake tract of the internal combustion engine can be identified based on the comparison result.

Description

[0001] The invention relates to a method for detecting a fault in the intake tract of an internal combustion engine and to a corresponding engine test device. In particular, the invention relates to a method for detecting coking in the intake tract of an internal combustion engine that has direct fuel injection, a throttle valve, and variable intake valve lift control.

[0002] In gasoline direct injection (GDI) engines, carbon buildup can occur in the intake tract, particularly on the intake valve (for example, on the valve stem) or in the intake port at the valve opening. This type of carbon buildup results in the accumulation of carbon-like material in the intake tract. The reason for this tendency in GDI engines is that, since the fuel is injected directly into the combustion chamber, there is no continuous cleaning scavenging of the intake tract, such as the intake valve, with gasoline. Oil residues from the crankcase ventilation, valve stem seals, or turbocharger bearings, combined with soot particles from the cylinder, can be deposited as carbon in the intake tract under the influence of heat. The tendency for carbon buildup tends to increase with the use of low-quality fuels and oils and with driving profiles characterized by low load.

[0003] This carbon buildup deteriorates engine smoothness during cold idling and can lead to increased fuel consumption and problems with warm-up performance. For example, a carbon deposit on the top of the valve stem between the valve head and valve stem can disrupt the tumble flow, causing more pronounced fluctuations in idle speed and, in extreme cases, even misfires. A carbon deposit can also act as a flow resistance due to insufficient cylinder filling, resulting in a loss of power. Furthermore, a carbon deposit on the intake valve or valve opening can prevent the valve from closing properly, leading to compression loss and sporadic misfires.

[0004] Typically, the degree of carbon buildup in the intake manifold can only be visually assessed in a workshop after disassembling engine parts. If the intake manifold is sufficiently carbonized, it is then cleaned or the affected components are replaced.

[0005] Visually detecting carbon buildup has the disadvantage of requiring significant effort to disassemble engine parts for visual inspection. Furthermore, visual assessment suffers from a lack of objectivity, as carbon buildup is difficult to evaluate through purely visual observation.

[0006] From DE 102 56 906 B4 a method for controlling an air / fuel mixture in an internal combustion engine is known, wherein an injected fuel mass is corrected for an adaptation of an air / fuel mixture ratio, so that in the case of multiple fuel injections with several injection processes for a combustion process in a cylinder of the internal combustion engine, the correction of the injected fuel mass is carried out for each injection process.

[0007] From DE 103 00 592 B4, a method is known for operating an internal combustion engine with a combustion unit and an actuator in an air supply for adjusting the air mass supplied to the combustion unit, wherein the position of the actuator is adapted to a current operating condition by means of a short-term adaptation, and wherein the position of the actuator is adapted to compensate for longer-term influencing factors on the position of the actuator by means of a long-term adaptation. Depending on the long-term adaptation value, a leakage in the air supply can be diagnosed.

[0008] DE 103 39 251 A1, DE 10 2016 219 067 A1 and DE 10 2010 035 026 A1 describe methods for operating an internal combustion engine, whereby the amount of air and fuel supplied to the combustion chamber is adjusted.

[0009] Methods for cleaning a combustion chamber of an internal combustion engine are known from DE 10 2006 034 633 A1 and DE 199 45 813 A1.

[0010] From DE 10 2011 005 283 B4, a method for detecting faulty components of an electronically controlled fuel injection system of an internal combustion engine is known.

[0011] From DE 10 2014 105 270 A1 a method for compensating or reducing an accumulation of coking residues on fuel injectors is known.

[0012] German patent application DE 10 2012 213 241 A1 discloses a method for detecting carbon buildup in the intake tract of an internal combustion engine with direct fuel injection without requiring engine disassembly and enabling an objective assessment of the carbon buildup. However, the method described therein can only be applied to internal combustion engines with variable valve timing (VVT) where the air mass flow is controlled by a throttle valve. In this method, the internal combustion engine is operated at idle with an increased idle speed compared to normal idle operation. Furthermore, the opening time of the intake valves is advanced by means of the VVT, thereby increasing the valve overlap (the duration for which the intake valve is already open before the exhaust valve is closed).A characteristic running roughness parameter of the combustion engine is then determined by measurement. Based on this running roughness parameter, the presence of carbon buildup in the intake manifold can then be detected.

[0013] However, this method cannot be used in internal combustion engines where the air mass flow is controlled by variable intake valve lift, because the combustion process is designed differently. While in an internal combustion engine with throttled load control the residual gas control is achieved via the intake, in an internal combustion engine with variable intake valve lift control the residual gas control is achieved via the exhaust.

[0014] The object of the invention is to provide a method for detecting a fault, in particular carbon buildup, in an internal combustion engine with direct fuel injection and variable intake valve lift control, which does not require disassembly of the internal combustion engine for detection and provides at least an indication of the presence of carbon buildup. Furthermore, the object is to provide an engine test device with corresponding properties.

[0015] This problem is solved by the features of the independent claims. Advantageous embodiments are specified in the dependent claims.

[0016] A first aspect of the invention relates to a method for detecting a defect, in particular carbon buildup, in the intake tract of an internal combustion engine. The internal combustion engine has one or more cylinder banks, each cylinder bank comprising several cylinders, each with a combustion chamber and at least one injection nozzle. In particular, exactly one injection nozzle is provided in each combustion chamber. A common air mass flow is supplied to the combustion chambers of each cylinder bank. Likewise, a common exhaust gas flow is discharged from the combustion chambers of each cylinder bank. The internal combustion engine has direct fuel injection; in particular, it is a gasoline direct injection engine.

[0017] The procedure runs, for example, on an external engine test device, such as one used in a vehicle repair shop. The engine test device is connected wirelessly or via cable to the vehicle's engine control unit (ECU) using a suitable vehicle interface and can also control the vehicle's operation and retrieve measured values ​​from the ECU. It is also conceivable that the procedure runs on the vehicle's ECU itself, in which case, for example, if a fault is detected, particularly carbon buildup, the system might initiate cleaning of the intake ports and / or intake valves. A cleaning instruction can be issued to the driver or a mechanic in the workshop, and / or a corresponding message can be stored in the vehicle's fault memory.It is also conceivable that if a fault is detected in the intake tract, in particular coking, the engine control unit will carry out an automatic cleaning of the vehicle, for example by introducing cleaning fluid into the intake tract or switching to a cleaning operating mode of the combustion engine.

[0018] The internal combustion engine features a throttle valve in the intake manifold and a variable intake valve lift (VVT). The variable intake valve lift allows for control of the valve lift. This variable lift regulates the amount of air entering each combustion chamber of the engine, eliminating the need for the throttle valve upstream of a cylinder bank during normal operation. The throttle valve is only used in special operating conditions, such as emergency running mode. This throttle-free load control reduces charge exchange losses. A higher airflow velocity leads to better mixing of the air-fuel mixture in the combustion chamber.

[0019] The procedure begins with an initial quantity deviation test. This test determines an initial air-fuel ratio value, calculated from a lambda value measured during the test and a desired lambda value for fuel combustion in the combustion chambers of the internal combustion engine. During this initial quantity deviation test, the engine's load is controlled using variable intake valve lift.

[0020] In a second step, a second quantity deviation test is performed. This second quantity deviation test determines a second air-fuel ratio value, which is calculated from a lambda value measured during the second quantity deviation test and a desired lambda value for fuel combustion in the combustion chambers of the internal combustion engine. During the second quantity deviation test, the internal combustion engine's load is controlled by the throttle valve located in the intake manifold.

[0021] In a third step, a comparison result is determined from the first air-fuel ratio value and the second air-fuel ratio value. Based on this comparison result, the presence of a fault in the intake tract of the internal combustion engine can be identified.

[0022] During the first and second quantity deviation tests, there is no change to the fuel path, i.e., the supply of the required fuel mass for combustion. In contrast, the air path is altered by the different load control methods, once via variable intake valve lift control and once via the throttle valve, if a fault or carbon buildup is present.

[0023] The method according to the invention allows for the objective detection of a defect, in particular coking, in the intake tract of an internal combustion engine with direct fuel injection. The objective detection is achieved through measurement rather than subjective visual assessment. Cleaning or repair is therefore only carried out when objectively necessary.

[0024] Disassembly of the internal combustion engine solely for the visual assessment of carbon buildup is not required when using the method described herein. Carbon buildup can be detected very quickly. For example, the time required to determine whether a fault exists in the intake tract of the internal combustion engine, particularly carbon buildup, can be reduced to approximately ten minutes instead of an hour or more when disassembling the engine. Using the described method, the engine no longer needs to be partially disassembled, thus minimizing further potential causes of future repairs to the absolute minimum. Furthermore, the accuracy of carbon buildup detection using a mixture deviation analysis method performed according to the invention is significantly higher than in the prior art.

[0025] The first and / or second quantity deviation test is best performed with the combustion engine idling. Control is achieved, as described above, by an external engine test device or the vehicle's engine control unit.

[0026] The first quantity deviation test is expediently performed with the throttle valve open and the intake valve lift small or even minimal. In other words, the first quantity deviation test is carried out in the so-called unrestricted state, where the amount of air introduced into the combustion chamber depends solely on the intake valve lift. Due to the selected small or minimal lift, the amount of air introduced into the combustion chamber will be noticeably reduced compared to the expected air volume if carbon deposits are present in the intake port or on the intake valve. Since the desired lambda value (i.e., the target lambda value) deviates more significantly from the measured lambda value, this manifests itself in a certain initial, excessively rich air-fuel ratio value.

[0027] In contrast, the second air-fuel ratio test is performed with the intake valve at maximum lift and the throttle valve largely closed. Load control is thus achieved via the throttle valve (so-called throttled operation). If carbon deposits are present in the intake port or on the intake valve, the second air-fuel ratio value will not deviate as much as in the first air-fuel ratio test, because the cross-section through which the air can flow into the combustion chamber is proportionally less affected by the carbon deposits than during the first air-fuel ratio test.

[0028] A fault in the intake tract, i.e., in the air path of the internal combustion engine, can therefore be inferred if the first air-fuel ratio and the second air-fuel ratio values ​​differ. In particular, the presence of carbon buildup in the intake tract is inferred if the first air-fuel ratio value is less than a predetermined first threshold value and the second air-fuel ratio value is greater than or equal to the predetermined first threshold value.

[0029] In contrast, a leak in the intake tract can be inferred if the first air-fuel ratio value is greater than a predefined second threshold and the second air-fuel ratio value is even higher than the predefined second threshold. This is evident from the fact that during the first quantity deviation test, there is hardly any vacuum at idle. A leak in the intake tract, particularly in the intake manifold, thus leads to an excessively lean fuel-air mixture. The first air-fuel ratio value is therefore greater than the predefined second threshold. During the second quantity deviation test, a high vacuum develops in the intake tract after the throttle valve, particularly in the intake manifold. A leak will therefore penetrate the intake tract or intake manifold, resulting in a far too lean fuel-air mixture.As a result, a second air-fuel ratio value is obtained, which is significantly larger than the second threshold value.

[0030] The first air-fuel ratio is calculated by dividing the lambda value measured during the first quantity deviation test by the desired lambda value. The second air-fuel ratio is calculated by dividing the lambda value measured during the second quantity deviation test by the desired lambda value.

[0031] Due to the preferred method of determining the first and second air-fuel ratio values, coking is present when the first air-fuel ratio value is lower than the specified threshold and therefore lower than the second air-fuel ratio value. This results from the fact that during the first quantity deviation test, with a given level of coking, a smaller quantity of air can flow into the combustion chamber than would be the case without coking. The measured lambda value is thus lower than the desired lambda value. In contrast, in the second quantity deviation test, the difference between the measured and the desired lambda value is not as large, since the coking does not alter the volume of air flowing into the combustion chamber to such a significant degree.

[0032] The first and second specified threshold values ​​are, in particular, equal in size, especially 1.

[0033] Furthermore, a computer program product is proposed that can be loaded directly into the internal memory of a digital computer and comprises software code sections that execute the steps of the procedure described herein when the product is running on a computer. The computer program product can be in the form of a data carrier, such as a DVD, a CD-ROM, a USB flash drive, and the like. The computer program product can also be in the form of a signal that can be loaded via a wireless or wired network.

[0034] A second aspect of the invention relates to an engine test device. This engine test device is designed to detect faults, particularly carbon buildup, in the intake tract of an internal combustion engine with direct fuel injection, a throttle valve, and variable intake valve lift control. The device can be connected to the vehicle for controlling its operation and receiving internal vehicle measurements, for example, via an electrical or radio connection. The engine test device controls the internal combustion engine via the engine control unit (ECU) so that the procedure described above is carried out.

[0035] The invention is described below with reference to the drawings and an exemplary embodiment. It shows: Fig. 1 An exemplary flowchart for a method according to the invention for detecting a defect, in particular coking, in the intake tract of an internal combustion engine.

[0036] In Fig. Figure 1 shows an exemplary flowchart of the inventive method for detecting a defect, in particular coking, in the intake tract of an internal combustion engine. The internal combustion engine has one or more cylinder banks, each cylinder bank comprising several cylinders, each with a combustion chamber and at least one injection nozzle. In particular, exactly one injection nozzle is provided in each combustion chamber. A common air mass flow is supplied to the combustion chambers of each cylinder bank. Likewise, a common exhaust gas flow is discharged from the combustion chambers of each cylinder bank. The internal combustion engine has direct fuel injection; in particular, it is a gasoline direct injection engine with fully variable valve timing.

[0037] In step S1, an initial quantity deviation test is performed, which determines an initial air-fuel ratio value w1. The air-fuel ratio value w1 is calculated as the quotient of the lambda value λ measured during the initial quantity deviation test. real , 1 and the desired lambda value λ soll , 1 (i.e., the target lambda value) of the fuel combustion in the combustion chambers of the internal combustion engine. In the first quantity deviation test, the internal combustion engine is load-controlled by means of variable intake valve lift control (VVT).

[0038] In step S2, a second quantity deviation test is performed, which determines a second air-fuel ratio value w2. The second air-fuel ratio value w2 is calculated as the quotient of the lambda value λ measured during the second quantity deviation test. real , 2 and the desired lambda value λ soll, 2 (i.e., a target lambda value) of the fuel combustion in the combustion chambers of the internal combustion engine.

[0039] In the second quantity deviation test, the load control of the combustion engine is carried out by means of the throttle valve in the intake tract of the combustion engine.

[0040] In step S3, the previously determined first and second air-fuel ratio values ​​w1 and w2 are compared. Based on the comparison result, it can be concluded whether a fault, in particular coking, is present in the intake tract of the internal combustion engine.

[0041] The first and second quantity deviation tests are performed one after the other while the combustion engine is idling.

[0042] The first quantity deviation test performed in step S1 is carried out with the intake valve at a small or minimum lift, with the throttle valve, located in the intake tract of the internal combustion engine, open. In other words, the first quantity deviation test is performed in the conventional operating mode of an internal combustion engine equipped with variable intake valve lift control.

[0043] In contrast, the second quantity deviation test in step S2 is performed with the intake valve at maximum lift (i.e., the intake valve is fully open) and the throttle valve largely closed. This operating mode corresponds to a limp-home mode, in which, for engines with variable intake valve lift control, load control is achieved via the throttle valve.

[0044] Depending on whether there is a fault in the intake tract and in particular coking, characteristic first and second air ratio values ​​w1, w2 result, whereby their ratio to each other allows the detection of the presence of a fault in the intake tract and in particular the presence of coking.

[0045] A general fault in the intake tract can be inferred if the first air-fuel ratio value w1, determined in step S1, and the second air-fuel ratio value w2, determined in the second step S2, differ. This results from the fact that the air-fuel ratio values ​​w1 and w2 should then have the same value if the lambda values ​​λ measured in steps S1 and S2, respectively, were equal. real , 1 and λ real, 2. The same amount of air should be introduced into the combustion chambers under different load control conditions, which should be reflected in the same measured lambda value. However, if the amount of air introduced into the combustion chambers differs between steps S1 and S2, this leads to differences in the lambda values ​​λ measured in steps S1 and S2. real , 1, λ real , 2, while the desired lambda values ​​λ soll , 1, λ soll , 2 remain unchanged.

[0046] Coking leads to the deposition of a carbon-like mass in the intake, particularly in the intake port and / or on the intake valve. The gradual accumulation of this carbon, especially during step S1 when the valve is only minimally open, disproportionately reduces the otherwise available airflow cross-section. This results in a smaller volume of air entering the combustion chamber, thus affecting the measured lambda value λ. real, 1 becomes smaller. This is noticeable as a decrease in the first air-fuel ratio value w1. If the first air-fuel ratio value w1 is smaller than the second air-fuel ratio value w2, coking can be inferred. The comparison can be made particularly against a predetermined threshold value set to 1, since the respective air-fuel ratio values ​​w1 and w2 correspond to the value 1 if no error is present, as the measured and desired lambda values ​​are then approximately equal. The reverse case, in which the first air-fuel ratio value w1 is larger than the predetermined threshold value and larger than the second air-fuel ratio value w2, suggests a leak in the intake tract, since, due to the flow conditions in the second step S2, in which the combustion engine is operated at reduced speed, less air is delivered to the combustion chamber.

[0047] It is particularly useful to perform the test described above on a cylinder-by-cylinder basis. For this purpose, the first air-fuel ratio value w1 and the second air-fuel ratio value w2 are determined for each cylinder individually, and a comparison is also made on a cylinder-by-cylinder basis. This makes it possible not only to make a general statement about the presence of a defect or coking, but also to identify the cylinder exhibiting the defect or to determine the defect intensity per cylinder.

[0048] In what way are the measured lambda values ​​λ used in the first step S1 and the second step S2? real , 1 or λ real , 2 and the desired lambda values ​​λ soll , 1 or λ soll The method for determining , 2 is generally known to those skilled in the art. One possible procedure is described, for example, in WO 2016 / 041 742 A1 of the applicant.

[0049] Furthermore, other procedures for determining a measured and a desired lambda value for each cylinder are known to those skilled in the art, so that a detailed description of the determination is omitted in the present description. Reference symbol list S1 Procedure step S2 process step S3 process step λ real , 1 measured lambda value in the first quantity deviation test λ real, 2 measured lambda value in the second quantity deviation test λ soll, 1 desired (target) lambda value in the first quantity deviation test λ soll, 2 desired (target) lambda value in the second quantity deviation test w1 first air ratio value w2 second air ratio value

Claims

[1] Method for detecting a fault, in particular coking, in the intake tract of an internal combustion engine with direct fuel injection, throttle valve and variable intake valve lift control, comprising the steps: a) Performing an initial quantity deviation test, by which an initial air-fuel ratio value (w1) is determined from a lambda value (λ) measured during the initial quantity deviation test real, 1 ) and a desired lambda value (λ soll, 1 ) the fuel combustion in the combustion chambers of the internal combustion engine, whereby in the first quantity deviation test a load control is carried out by means of the variable intake valve lift control; b) Performing a second quantity deviation test to determine a second air-fuel ratio value (w2) from a lambda value (λ) measured during the second quantity deviation test real, 2 ) and a desired lambda value (λ soll, 2) the fuel combustion in the combustion chambers of the internal combustion engine, whereby in the second quantity deviation test a load control is carried out by means of the throttle valve; c) Determining a comparison result from the first air ratio value (w1) and the second air ratio value (w2), whereby the presence of a fault in the intake tract of the internal combustion engine can be identified based on the comparison result. [2] Method according to claim 1, wherein the first and / or the second quantity deviation test is carried out in idle operation of the internal combustion engine. [3] Method according to claim 1 or 2, wherein the first quantity deviation test is performed with a small or minimal stroke of the inlet valve and an open throttle valve. [4] Method according to one of the preceding claims, wherein the second quantity deviation test is carried out with the inlet valve at maximum stroke and the throttle valve largely closed. [5] Method according to one of the preceding claims, wherein the first air ratio value (w1) and the second air ratio value (w2) are determined cylinder-specifically, and the comparison result is determined cylinder-specifically. [6] Method according to one of the preceding claims, wherein the first air ratio value (w1) is determined by the quotient of the lambda value (λ) measured during the first quantity deviation test. real, 1 ) and the desired lambda value (λ soll, 1 ) is formed and the second air ratio value (w2) is determined by the quotient of the lambda value (λ) measured during the second quantity deviation test. real, 2 ) and the desired lambda value (λ soll, 2 ) is formed. [7] Method according to any of the preceding claims, wherein the presence of a defect in the inlet tract is inferred if the first air ratio value (w1) and the second air ratio value (w2) are different. [8] Method according to one of the preceding claims, wherein the presence of coking in the inlet tract is inferred if the first air ratio value (w1) is less than a predetermined first threshold value and the second air ratio value (w2) is greater than the predetermined first threshold value. [9] A method according to any of the preceding claims, wherein the presence of a leak in the inlet tract is inferred if the first air ratio value (w1) is greater than a predetermined second threshold value and the second air ratio value (w2) is increased again more than the predetermined second threshold value (w2). [10] Method according to one of claims 8 and 9, wherein the predetermined first and the predetermined second threshold are equal, in particular 1. [11] Computer program product that can be loaded directly into the internal memory of a digital computer and comprises software code sections with which the steps according to any one of claims 1 to 10 are performed when the product is running on a computer [12] Engine test device for detecting faults in the intake tract of an internal combustion engine, which is designed to perform the method according to any one of claims 1 to 10.

Images