Method for determining fuel leaks into combustion chambers of an internal combustion engine

Abstract

A method for operating an internal combustion engine (100) comprising one or more combustion chambers (12), a direct injection system (20), an ignition system (30), and a starter system (40) is proposed, wherein the method comprises bringing the internal combustion engine (100) from a standstill to a rotating state, wherein bringing the internal combustion engine (100) from a standstill to a rotating state comprises starting the engine by means of the starter system (40) and activating direct injection by means of the direct injection system (20), wherein, prior to activating the direct injection, the ignition system (30) is activated so that, if combustible leakage fuel is present in the combustion chambers (12), it is combusted by means of ignition sparks provided by the ignition system, and wherein the internal combustion engine (100) is configured to operate for a period of time,While the ignition system (30) is already activated and the direct injection is not yet activated, a measurement is to be acquired and evaluated that is influenced by mechanical work performed by the combustion of a fuel-air mixture comprising the leakage fuel present in the combustion chambers (12). An internal combustion engine (100) operable using the method, as well as a computing unit and a computer program for carrying out the method, are also proposed.

Description

The present invention relates to a method for determining fuel leakage into combustion chambers of an internal combustion engine and an internal combustion engine operable using the method, as well as a computing unit and a computer program for carrying out the method. Background of the invention Internal combustion engines with gasoline direct injection use high-pressure injection valves or injectors, which are also referred to simply as "injectors" below, to introduce the fuel required for combustion into the combustion chambers. The injectors are typically mounted in the cylinder head. When the injectors are activated, the fuel is injected directly into the combustion chambers through injection holes. Typical injection pressures for gasoline direct injection are up to 500 bar. When the injector is closed, i.e., not actuated, the fuel is sealed to the combustion chamber via suitable sealing surfaces. However, due to manufacturing tolerances, a certain amount of leakage cannot always be completely avoided with a closed injector. Such leakage is subsequently referred to as "injector leakage." The leakage rate from injectors is typically so low that no negative impact on combustion is to be expected when the internal combustion engine is running. This is because the time between two combustion cycles is very short. During extended periods of inactivity, i.e., times when the injector is not activated but fuel is present under pressure at the injector, a considerable amount of fuel can accumulate due to injector leakage. This fuel is deposited in the combustion chamber and, during the subsequent start-up, a large portion is expelled unburned from the combustion chamber due to the gas exchange. Conversion in the catalytic converter also does not occur due to insufficient temperature during a cold start, so some of the unburned fuel is emitted into the environment, leading to a deterioration of emissions. Besides fuel entering the combustion chamber from injector leakage, a fuel mixture capable of ignition during startup can also result from leaks in the fuel tank venting system or the crankcase ventilation. Injector leaks typically occur on a cylinder-by-cylinder basis. Other leaks are distributed across all cylinders depending on their point of entry. Until now, reliable detection of the relatively small specified injector leakage rates has not been possible due to insufficient indicators. Only with larger leaks, typically many times the specified leakage value, was a diagnosis theoretically possible using conventional methods. Disclosure of the invention According to the invention, a method for determining fuel leakage into the combustion chambers of an internal combustion engine, an internal combustion engine operable using the method, a computing unit, and a computer program for carrying out the method with the features of the independent claims are proposed. Advantageous embodiments are the subject of the dependent claims and the following description. The proposed method is for determining fuel leakage into one or more combustion chambers of an internal combustion engine, which has one or more combustion chambers, a direct injection system, an ignition system, and a starter system. The method comprises bringing the internal combustion engine from a standstill to a rotating state, wherein bringing the internal combustion engine from a standstill to a rotating state includes cranking by means of the starter system and activating direct injection by the direct injection system. Prior to activating the direct injection, the ignition system is activated so that, if combustible leakage fuel is present in the combustion chambers, it is combusted by means of ignition sparks provided by the ignition system. During a period in which the ignition system is already activated and the direct injection is not yet activated,A measurement is recorded and evaluated, which is influenced by mechanical work performed by the combustion of a fuel-air mixture containing the leaking fuel present in the combustion chambers. The fuel-air mixture can also consist essentially of the leaking fuel in its fuel component. Leakage fuel specifically includes fuel present in the combustion chambers solely due to leaks, and not fuel actively injected into the combustion chambers by the high-pressure injectors. As explained earlier, leakage fuel can enter the combustion chambers through injector leaks, but also, for example, through a tank venting system or the crankcase ventilation. A key aspect of the present invention is to activate the ignition in the internal combustion engine as early as possible, certainly earlier than in conventional methods, so that it is possible to combust an existing fuel-air mixture even without active injection. For this purpose, the ignition is activated, in particular, immediately after the engine position is detected. The ignition is then triggered, especially in the region of top dead center, so that combustion is initiated at the correct time. This results in a positive torque being applied to the crankshaft drive, and on this basis, the mechanical work, which is used to detect leaks, is performed in a standardized and reproducible manner. At top dead center, the leaking fuel may already be largely vaporized due to the heat of compression, thus increasing its ignitability even at cold temperatures. During combustion, the leaking fuel (hydrocarbon) is converted into carbon dioxide and water, and possibly also carbon monoxide and nitrogen oxides, depending on the completeness of the combustion. The combustion of the leaking fuel during the aforementioned period between the activation of the ignition system and the injection system performs mechanical work, which affects, for example, the engine speed, but also the starter torque or the starter current draw, and can therefore be used to determine the quantity or, more generally, the presence of the leaking fuel. Based on the typically available knowledge of the time elapsed since the last start or the last time the ignition was activated, as well as other parameters such as fuel pressure, the leakage rate per unit of time can be determined.Depending on the engine's shutdown position, this can also prevent or at least reduce the expulsion of unburned hydrocarbons from the combustion chambers. Within the scope of the present invention, the fuel accumulated during the shutdown phase due to injector leakage, as well as hydrocarbons from other sources (crankcase ventilation, tank venting, etc.), are combusted as early as possible during the subsequent start-up, allowing the amount of leakage to be determined. If a quantitative determination of the leakage amount is not possible, it can at least be determined that sufficient leakage fuel is present to initiate combustion. Based on this, the proportion of unburned hydrocarbons during start-up can be reduced by implementing suitable measures. This also minimizes the release of pollutants, i.e., hydrocarbon emissions. In embodiments of the proposed method, the measured value, which is influenced by mechanical work performed by the combustion of the fuel-air mixture present in the combustion chambers, or a corresponding measured value profile, is correlated with an engine position. Based on this correlation, the combustion chamber with an increased amount of leaked fuel can be identified. This increased amount of leaked fuel results primarily from a leaking high-pressure injector, since other leaks, as explained above, typically do not have a combustion chamber-specific effect. In embodiments of the proposed method, as previously mentioned in other words, the ignition system is activated such that the spark plugs are generated when the pistons corresponding to the combustion chambers are at top dead center. This enables a standardized measurement of the mechanical work performed. For this purpose, engine position detection can be carried out in a known manner, particularly before the ignition system is activated or the respective spark plugs are generated. This can serve to identify the leaking high-pressure injector. As mentioned, in embodiments of the proposed method, for example, a speed signal, starter torque and / or starter current consumption, as well as other derived quantities, can be used as the measured value influenced by the mechanical work performed by the combustion of the fuel-air mixture present in the combustion chambers. The use of additional sensor values ​​or complex measurements (evaluation of multiple indicators) is not necessary, since the aforementioned signals or values ​​are typically present in an internal combustion engine anyway. In some embodiments of the proposed method, no fuel is introduced into the combustion chambers by actuating the direct injection injectors prior to the activation of the direct injection system. Therefore, the combustion resulting from the early activation of the ignition system only affects the amount of fuel introduced through leaks during the vehicle's standstill. In embodiments of the proposed method, the internal combustion engine can be part of a hybrid vehicle, which also includes an electric motor for propelling the hybrid vehicle. The transition of the internal combustion engine from standstill to rotation occurs after purely electric operation of the hybrid vehicle. Significant leakage can also occur during corresponding purely electric operating phases. In various embodiments of the proposed method, the injectors can have a nominal or measured leakage rate, allowing for an estimation of the amount of fuel introduced through corresponding injector leakage. The proposed method and its embodiments then enable a determination of whether the nominal or measured leakage rate has been exceeded. This can be particularly relevant for currently typical specified leakage rates, and at least when the leakage rates are not very small. As a response, certain measures, such as replacing or repairing the affected high-pressure injector, may be necessary. The proposed internal combustion engine comprises one or more combustion chambers, a direct injection system, an ignition system, and a starter system, wherein the internal combustion engine is configured for transitioning from a standstill to a rotating state, the transition from standstill to a rotating state includes cranking by means of the starter system and activation of direct injection by the direct injection system, wherein the internal combustion engine is configured to activate the ignition system before activating the direct injection, so that, if combustible leakage fuel is present in the combustion chambers, it is combusted by means of ignition sparks provided by the ignition system, and wherein the internal combustion engine is configured to perform a measurement and evaluation during a period in which the ignition system is already activated and the direct injection is not yet activated.which is influenced by mechanical work performed by the combustion of a fuel-air mixture present in the combustion chambers, which includes the leaked fuel. The internal combustion engine is specifically designed to carry out a process as previously described in its various configurations. These configurations benefit from the advantages explained for the corresponding process variants in the same way, and reference can therefore be made to them. A computing unit according to the invention, e.g., a control unit of a motor vehicle, is configured, particularly in terms of programming, to cause an internal combustion engine to carry out all process steps of a process as previously explained in embodiments. Reference can also be made to the above explanations regarding the features and advantages of the computing unit. This also applies to the proposed computer program, which causes a computing unit to cause an internal combustion engine to carry out all process steps of a process in the previously explained configurations when this is executed on the computing unit. Implementing a method according to the invention in the form of a computer program or computer program product with program code for carrying out all method steps is advantageous, as this incurs particularly low costs, especially if an executing control unit is also used for other tasks and is therefore already available. Finally, a machine-readable storage medium is provided, containing a computer program as described above. Suitable storage media or data carriers for providing the computer program include, in particular, magnetic, optical, and electrical storage media, as are known in the relevant field. Downloading a program via computer networks is also possible. Such a download can be wired or wireless. Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawing. The invention is schematically illustrated in the drawing using exemplary embodiments and is described below with reference to the drawing. Brief description of the drawings Fig. 1 illustrates a partial view of an internal combustion engine. Fig. 2 illustrates a partial view of an internal combustion engine controlled according to a non-inventive embodiment. Fig. 3 illustrates an internal combustion engine controlled according to a proposed embodiment in three states. Fig. 4 illustrates aspects of a method according to a proposed embodiment in the form of signal diagrams. Fig. 5 illustrates aspects of a method according to a proposed embodiment in the form of signal diagrams. Fig. 6 illustrates aspects of a method according to a proposed embodiment in the form of signal diagrams. Detailed description The embodiments described below are provided solely to assist the reader in understanding the claimed and previously explained features. They represent only representative examples and are not intended to be considered exhaustive or limiting with regard to the features of the invention. It is understood that the advantages, embodiments, functions, features, structures, and / or other aspects described above and below are not to be considered limitations of equivalents to the claims, and that other embodiments may be used and modifications made without deviating from the scope of the claimed invention. Different embodiments of the invention may include, have, consist of, or essentially consist of further advantageous combinations of the described elements, components, features, parts, steps, means, etc., even if such combinations are not specifically described here. Explanations relating to devices, apparatus, arrangements, systems, etc., according to embodiments of the present invention may also apply to methods, processes, procedures, etc., according to embodiments of the present invention, and vice versa. Identical, functionally equivalent, structurally identical, or comparably constructed elements, process steps, etc., may be indicated by identical reference numerals. The conjunction "and / or," when used before the last item in a list, should be understood to mean that all the items in the list can be combined with each other in any way. In other words, "A, B and / or C" means "A and / or B and / or C" or "at least one of the elements A, B, C in any combination." As mentioned, a key aspect of the present invention is to activate the ignition in the gasoline engine as early as possible, so that even without active injection, it is possible to burn the fuel-air mixture present in the combustion chambers. The ignition in the gasoline engine can be activated immediately after the engine position is detected. The engine position can either be determined from the previous driving cycle based on coast-down detection or is detected at the start of crankshaft rotation using the crankshaft sensor and / or camshaft sensor. Depending on the configuration, the position is determined no later than after 180° or 360° of crankshaft rotation. Knowing the engine position allows the ignition coil to be controlled correctly, so that the spark can initiate combustion at the spark plug at the desired time (top dead center). This also allows any fuel-air mixture that may be present (from leakage) to be burned, even without active fuel injection. During combustion, the fuel (hydrocarbon) is converted into carbon dioxide and water, and possibly also carbon monoxide and nitrogen oxides, depending on the completeness of the combustion. Depending on the engine's position when switched off, the emission of unburned hydrocarbons can be avoided or at least reduced. Figure 1 shows a partial view of an internal combustion engine 100, specifically a cylinder 10 with a piston 11 and a combustion chamber 12, as well as an injector 13, a spark plug 14, an intake valve 15, an exhaust valve 16, an intake manifold 17, and an exhaust pipe 18. A direct injection system 20, an ignition system 30, and a starter system 40 are illustrated in a highly simplified manner, with the injector 13 being part of the direct injection system 20 and the spark plug 14 being part of the ignition system. The internal combustion engine 100 can, in particular, be part of a hybrid vehicle, so that a starter system 40 can also include an electric motor for the electric drive of the hybrid vehicle. A control unit is schematically designated 50. Fig. 1 shows the state after a prolonged standstill of the internal combustion engine 100, such that, as illustrated by the dots, fuel has accumulated in the combustion chamber over a certain period of time from an injector leakage of the injectors 13. This results from the fuel pressure present at the injector 13. The amount of fuel that has entered the combustion chamber 12 depends on the degree of leakage, the elapsed time, and the fuel pressure at the injector 13. Figure 2 illustrates essentially the same elements as Figure 1. For the sake of clarity, these will not be explained again here, and reference is made to the explanations for Figure 1. Fig. 2 shows how, according to a conventional method, the internal combustion engine 100 is started with fuel present in the combustion chamber 12 until a certain speed is reached and, if necessary, until further criteria such as rail pressure or intake manifold vacuum are met, without activation of injection. As illustrated by arrow 11a, the piston 11 is moved upwards and displaces the fuel in the combustion chamber 12, so that it flows out through the exhaust valve 18, as illustrated by arrow 18a, into the exhaust pipe 18. The outflow of unburned fuel, as illustrated in Fig. 2, can lead to the negative effects described above, especially since, as mentioned, the catalyst is not necessarily at operating temperature and therefore unburned hydrocarbons are released into the environment. The measures proposed here overcome these problems, as illustrated in three partial views A to C of Fig. 3. A downward piston movement is indicated by arrow 11b, and an upward piston movement by arrow 11a, as before. Partial views A to C of Fig. 3 again show essentially the same elements as in Figs. 1 and 2, although the direct injection system 20, the ignition system 30, the starter system 40, and the control unit 50 are not shown again due to their lack of direct relevance. For the sake of clarity, the components shown again will not be explained again, and reference is made to the explanations for Fig. 1 with regard to Fig. 3. Depending on the position of the internal combustion engine 100 when it is switched from a standstill to a rotating state, additional fresh air may initially be drawn into certain cylinders 10, as shown in View A of Fig. 3. When the rotation of the internal combustion engine 100 begins during the compression stroke of a cylinder 10, the fuel from the leakage is compressed directly together with the air from the preceding run-out of the internal combustion engine 100. This is shown in View B of Fig. 3. In the region of top dead center or shortly thereafter, the compressed fuel-air mixture is ignited and burned, as shown in View C of Fig. 3, where an area hatched with short horizontal lines represents the combustion zone. This causes the piston to move downwards and transmit force to a crankshaft K via a connecting rod P shown in Partial View C of Fig. 3.The work performed during the combustion of the leaked fuel thus becomes effective in terms of torque or rotational speed. In contrast to the step shown in Fig. 2, which is not according to the invention, no unburned fuel is emitted according to the proposed embodiments, but rather the combustion gases, which ideally consist only of carbon dioxide and water. Figure 4A shows diagrams relating to a conventional method, as illustrated in Figure 2. The diagrams in Figure 4B relate to a proposed embodiment. In Figures 4A and 4B, signals or measured values ​​are plotted against time in seconds on the horizontal axis. The upper diagram in Figures 4A and 4B each depicts a single engine speed curve, with crankshaft rotation beginning at 30.6 seconds according to Figure 4A, i.e., the internal combustion engine 100 starting to rotate at this point. Only at approximately 31.05 seconds, in the non-inventive method according to Figure 4A, are the direct injection system 20 and the ignition system 30 activated, as illustrated in the middle and lower diagrams, which show the corresponding control signals. According to Fig. 4B, crankshaft rotation begins just before 43.4 seconds. Around this time, at approximately 43.4 seconds, the ignition system 30 is activated, as illustrated in the lower diagram. Subsequently, at approximately 43.9 seconds, the direct injection system 20 is activated, as shown in the middle diagram. The proposed method and its embodiments are fundamentally applicable to any internal combustion engine (four-stroke gasoline engine). In engines with gasoline direct injection, this can reduce the negative impact on emissions caused by leakage in the high-pressure injection valve. The implementation for early ignition activation can be carried out in the engine control unit (via software). No additional components (sensors or actuators) are required for implementation. Therefore, the invention can be used in current and future projects and engine control systems. Figure 5 shows the curves of rotational speed R and starter torque M on the vertical axis versus time in seconds on the horizontal axis in an upper diagram. A lower diagram shows the curve of a position signal from a typical engine position sensor on the vertical axis versus the same time axis. The start of the internal combustion engine, for example, the activation of a starter system 40, is indicated by S, and the start of the ignition system 30 by Z. As can be seen, there is a drop in the starter torque M at approximately 52.5 seconds, which indicates significant amounts of leakage fuel and thus an ignitable fuel-air mixture in a combustion chamber 12. The processes illustrated in Fig. 5 are each based on a method configuration in which, as soon as the engine position is detected, the ignition is activated, so that the ignitable fuel-air mixture, which includes leakage fuel, is ignited and burned. The resulting mechanical work, or the corresponding torque, leads to an increase in the speed gradient, as also shown in Fig. 5, and to a reduction in the starter torque, as discussed. Figure 6 again illustrates the curves of rotational speed and starter torque on the vertical axis versus time in seconds on the horizontal axis. The rotational speed curve without leakage fuel is denoted by R1, and the curve with leakage fuel is denoted by R2. The starter torque curve without leakage fuel is denoted by M1, and the curve with leakage fuel is denoted by M2. As can be seen in Figure 6, the rotational speed curve R2 increases due to the combustion of the leakage fuel. The starter torque M2 required to rev the engine during startup is significantly reduced compared to the curve M1 without leakage fuel due to the combustion and the positive engine torque. The rotational speed curve R1 remains constant in this range.

Claims

Method for determining fuel leakage into one or more combustion chambers (12) of an internal combustion engine (100) comprising the one or more combustion chambers (12), a direct injection system (20), an ignition system (30) and a starter system (40), the method comprising: - bringing the internal combustion engine (100) from standstill to a rotating state, wherein bringing the internal combustion engine (100) from standstill to a rotating state includes starting by means of the starter system (20) and activating direct injection by means of the direct injection system (20), and - activating the ignition system (30) prior to activating the direct injection, such that, if combustible leakage fuel is present in the combustion chambers (12), it is combusted by means of ignition sparks provided by the ignition system (30), and - during a period of time,while the ignition system (30) is already activated and the direct injection is not yet activated, detecting and evaluating a measured value that is influenced by mechanical work performed by the combustion of a fuel-air mixture present in the combustion chambers (12), which includes the leakage fuel. The method of claim 1, wherein the leakage fuel comprises fuel present due to leaks in the combustion chambers, which has entered the combustion chambers (12) through injector leaks, through a tank venting system and / or a crankcase vent. Method according to claim 1 or 2, wherein the measured value, which is influenced by the mechanical work performed by the combustion of the fuel-air mixture present in the combustion chambers, or a corresponding measured value profile, is correlated with an engine position. Method according to one of the preceding claims, wherein the ignition system is activated such that the ignition sparks are provided when pistons (11) associated with the combustion chambers are at top dead centers. Method according to one of the preceding claims, wherein a speed signal of the internal combustion engine and / or a starter torque and / or a starter current consumption is used as the measured value which is influenced by the mechanical work performed by the combustion of the fuel-air mixture present in the combustion chambers. Method according to one of the preceding claims, wherein the internal combustion engine is part of a hybrid vehicle which further comprises an electric machine for driving the hybrid vehicle, wherein the transition of the internal combustion engine from standstill to the rotating state takes place after purely electric operation of the hybrid vehicle. Method according to one of the preceding claims, wherein no fuel is introduced into the combustion chambers (12) prior to the activation of the direct injection by actuating injectors (13) of the direct injection system (20). Method according to claim 7, wherein the injectors (13) have a nominal or determined leakage rate. Internal combustion engine (100) comprising a number of combustion chambers (12), a direct injection system (20), an ignition system (30) and a starter system (40), wherein the internal combustion engine (100) is configured for transitioning from a standstill to a rotating state, wherein the transition from a standstill to a rotating state comprises starting by means of the starter system (40) and activation of direct injection by the direct injection system (20), wherein the internal combustion engine (100) is configured to activate the ignition system (30) prior to activating the direct injection, so that, if combustible leakage fuel is present in the combustion chambers (12), it is combusted by means of ignition sparks provided by the ignition system (30), and wherein the internal combustion engine (100) is configured to operate during a period in which the ignition system (30) is already activated and the direct injection is not yet activated,to record and evaluate a measured value that is influenced by mechanical work performed by the combustion of a fuel-air mixture present in the combustion chambers (12), which includes the leakage fuel. Internal combustion engine (100) configured to carry out a method according to any one of claims 1 to 8. Computing unit configured to cause the internal combustion engine (100) according to claim 9 or 10 to carry out all process steps of a process according to any one of claims 1 to 8. Computer program that causes the computing unit according to claim 11 to cause the internal combustion engine (100) to carry out all process steps of a method according to any one of claims 1 to 8 when the computer program is executed on the computing unit. Machine-readable storage medium with a computer program stored thereon according to claim 12.

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