Method for adapting a mixture formation of an internal combustion engine

Abstract

Method for adapting a mixture formation of an internal combustion engine (10), in particular a hydrogen burner, with several cylinders (n), wherein the internal combustion engine (10) has a NOx sensor (NOx) in an exhaust system, where a NOx sensor signal (NOx sens ) is determined by a control unit (115), Starting with one cylinder (n), the mixture of the respective cylinder (n) is enriched one after the other up to a predeterminable NOx limit value (S NOx ) is carried out, where for each cylinder (n) a first relative fuel quantity (rk 1,n ) is determined before the respective cylinder (n) is enriched, After enrichment, a second relative fuel quantity (rk 2,n ) is determined for the respective cylinder (s) and the enrichment of the respective cylinder (s) is reversed, where for each cylinder (n) a difference (D n ) between the determined second relative fuel quantity (rk 2,n ) and the determined first relative fuel quantity (rk 1,n ) is determined, depending on the differences determined (D n ) an averaged relative fuel quantity (rk m ) is determined, where for each cylinder (n) depending on the determined difference (D n ) and the averaged relative fuel quantity (rk m ) an adaptation of the mixture formation for the internal combustion engine (10) is carried out.

Description

[0001] The present invention relates to a method for adapting a mixture formation of an internal combustion engine as well as a computing unit and a computer program for carrying out the method. State of the art

[0002] One possible fuel injection method for gasoline engines is manifold injection, which is increasingly being replaced by direct fuel injection. The latter method leads to significantly better fuel distribution in the combustion chambers and thus to improved power output with lower fuel consumption.

[0003] There are also gasoline engines with a combination of port injection and direct injection, a so-called dual system. This is particularly advantageous in light of increasingly stringent emissions requirements and limits, as port injection results in better emissions than direct injection, for example, at medium loads. At full load, however, direct injection enables a reduction in knocking. Disclosure of the invention

[0004] The object of the invention is to provide an adaptation of a mixture formation of an internal combustion engine, wherein the mixture formation of the fuel injection is adapted.

[0005] In a first aspect, the invention relates to methods for adapting a mixture formation of an internal combustion engine, in particular a hydrogen combustion engine, with several cylinders, wherein the internal combustion engine has a NOx sensor in an exhaust system, wherein a NOx sensor signal is continuously determined by a control unit, wherein a target lambda value for the internal combustion engine is specified by a control strategy calculated on the control unit, starting with one cylinder after another, the mixture of the respective cylinder is enriched up to a predefined NOx limit value, whereby a first relative fuel quantity is determined for each cylinder before the respective cylinder is enriched, after enrichment has been completed, a second relative fuel quantity is determined for each cylinder and the enrichment of the respective cylinder is reversed, wherein for each cylinder a difference between the determined second relative fuel quantity and the determined first relative fuel quantity is determined, whereby an average relative fuel quantity is determined depending on the differences determined, For each cylinder, an adaptation of the mixture formation for the internal combustion engine is carried out depending on the determined difference and the averaged relative fuel quantity.

[0006] Advantageously, the method for adapting the mixture formation of a multi-cylinder internal combustion engine enables individual adjustment of the mixture of each cylinder based on the measured NOx value. In contrast to conventional mixture adaptations using lambda signals, the NOx signal is less dependent on the O2 concentration in the exhaust gas and thus on the lambda value.

[0007] The method also has the particular advantage that mixture deviations of the individual cylinders can be determined and corrected depending on the NOx emissions in relation to the lambda threshold.

[0008] The determination of the mixture deviation is simple and robust due to the exponential behavior of NOX emissions via lambda in relation to the predefined NOX limit. When the NOX limit is reached, the lambda threshold is also defined. This is determined in a calibration phase for the combustion engine and then stored in the control unit.

[0009] This prevents a cylinder from operating in an area that would result in high NOx emissions.

[0010] The invention also addresses the problem of cylinder imbalance by measuring and adjusting each cylinder's deviations from the average distance. This ensures that all cylinders have the same mixture state, resulting in consistent combustion and power development.

[0011] The use of the NOx sensor and the reduced dependence on the oxygen concentration in the exhaust gas offer significant advantages over conventional lambda-based adjustments.

[0012] Overall, the process enables precise mixture adaptation and optimization of the mixture position in hydrogen engines to ensure low NOx emissions and exploit the engine's performance potential.

[0013] In a special embodiment, approval is given for the adaptation of the mixture formation when a stationary or quasi-stationary operating state exists for the internal combustion engine.

[0014] The advantage of this special design is that the release for mixture adjustment is only granted during steady-state or quasi-steady-state operating conditions of the internal combustion engine. This means that mixture adjustment is not active during dynamic operating phases, such as acceleration or load changes. This ensures stable and reliable mixture formation during these critical operating phases.

[0015] This helps improve engine performance, efficiency and durability.

[0016] In an advantageous embodiment, during the enrichment of one cylinder, the mixture of the others is adjusted in such a way that a target lambda value for the internal combustion engine is kept constant.

[0017] The advantage of this advantageous design is that while enriching one cylinder, the mixture of the remaining cylinders is adjusted so that the overall air-fuel mixture is kept constant. This means that enriching a single cylinder does not lead to excessive enrichment of the overall mixture.

[0018] Thus, the procedure can be carried out robustly and the mixture position of the enriched cylinder can be determined.

[0019] In a special embodiment, if the difference falls below the averaged relative fuel quantity, the mixture for the respective cylinder is leaned out.

[0020] The advantage of this special design is that if the difference falls below the average relative fuel quantity, the mixture for the respective cylinder is leaned out. This allows for targeted adjustment of the mixture to ensure optimal combustion and power development.

[0021] Leaning the mixture increases the air-fuel ratio by injecting less fuel. This can help reduce fuel consumption and improve engine efficiency. Optimal combustion with a lean mixture can also lead to a reduction in pollutant emissions.

[0022] In a special embodiment, if the difference exceeds the average relative fuel quantity, the mixture is enriched for the respective cylinder.

[0023] Enriching the mixture increases the amount of fuel delivered to that cylinder. This can help compensate for any imbalances between cylinders and ensure that all cylinders operate under similar conditions. Uniform combustion results in improved engine performance and reduces the risk of damage or wear to individual cylinders.

[0024] In an advantageous embodiment, the mixture is leaned to the value of the averaged relative fuel quantity.

[0025] This allows for targeted adjustment of the mixture for each cylinder to achieve optimal combustion and power development. Overall, leaning the mixture to the value of the averaged relative fuel quantity enables targeted optimization of combustion and power development. Adjusting the fuel quantity ensures even combustion in all cylinders, resulting in improved engine performance, lower emissions, and a longer engine life.

[0026] In a further embodiment, the enrichment of the mixture is carried out to the value of the averaged relative fuel quantity.

[0027] This allows for targeted adjustment of the mixture for each cylinder to achieve optimal combustion and power development. Overall, enriching the mixture to the value of the averaged relative fuel quantity enables targeted optimization of combustion and power development. Adjusting the fuel quantity ensures even combustion in all cylinders, resulting in improved engine performance, lower emissions, and a longer engine life.

[0028] In an advantageous embodiment, the NOx sensor signal is continuously recorded for each cylinder during enrichment, and if the NOx sensor signal exceeds a predeterminable NOx limit value, an enable for the method is granted, and if the NOx sensor signal falls below the enable threshold value, the measurement for this cylinder is discarded and the measurement for the next cylinder is continued.

[0029] If the NOx sensor signal falls below the release threshold, the measurement for that cylinder is discarded and the measurement continues for the next cylinder. This enables efficient and rapid adjustment of the mixture for each cylinder. If a cylinder already falls below the NOx limit, no further adjustments are necessary because that cylinder already has optimal emission levels. Therefore, the measurement for that cylinder can be skipped to save time and resources. By continuously recording the NOx sensor signal for each cylinder and specifically adjusting the mixture based on the NOx emissions, the process can enable precise and individual enrichment for each cylinder. This leads to a further reduction in NOx emissions and improved engine performance.

[0030] In further aspects, the invention relates to a device, in particular a control unit and a computer program, which are configured, in particular programmed, to execute one of the methods. In yet another aspect, the invention relates to a machine-readable storage medium on which the computer program is stored. Description of the embodiments

[0031] The invention is described in more detail below with reference to the accompanying drawings and exemplary embodiments. Fig. 1 a schematic representation of a cylinder of an internal combustion engine, Fig. 2 a diagram illustrating the process for mixture formation of an internal combustion engine with a dual fuel metering device

[0032] In Fig. Figure 1 schematically illustrates a cylinder 102 of the internal combustion engine 100. The cylinder 102 has a combustion chamber 103, which is enlarged or reduced by the movement of a piston 104. The present internal combustion engine may, in particular, be a gasoline engine, a diesel engine, or a hydrogen combustion engine.

[0033] Cylinder 102 has an intake valve 105 for admitting air or a fuel-air mixture into combustion chamber 103. The air is supplied via intake manifold 106 as part of an air supply system, where fuel injector 107 is located. Intake air is admitted into combustion chamber 103 of cylinder 102 via intake valve 105. A throttle valve 112 in the air supply system serves to adjust the required air mass flow into cylinder 102. Furthermore, an air mass sensor 99 for measuring the relative air mass is provided in intake manifold 106, particularly upstream of throttle valve 112. This can, in particular, be a hot-film air mass meter (HFM).

[0034] The internal combustion engine can be operated using intake manifold injection. With the help of the fuel injector 107, fuel is injected into the intake manifold 106, forming an air-fuel mixture there, which is then admitted into the combustion chamber 103 of the cylinder 102 via the intake valve 105.

[0035] The internal combustion engine can also be operated using direct injection. For this purpose, the fuel injector 111 is mounted on the cylinder 102 to inject fuel directly into the combustion chamber 103. With this direct injection, the air-fuel mixture required for combustion is formed directly in the combustion chamber 103 of the cylinder 102. The cylinder 102 is further provided with an ignition device 110 to generate an ignition spark to start combustion in the combustion chamber 103.

[0036] After combustion, combustion exhaust gases are expelled from cylinder 102 via an exhaust pipe 108. Expulsion occurs depending on the opening of an exhaust valve 109, which is also arranged on cylinder 102. Intake and exhaust valves 105, 109 are opened and closed to carry out four-stroke operation of internal combustion engine 100 in a known manner. A lambda sensor can be used to determine the lambda value of the exhaust gas in exhaust pipe 108.

[0037] The internal combustion engine 100 can be operated with direct injection, with intake manifold injection, or in mixed operation. This allows the selection of the optimal operating mode for operating the internal combustion engine 100 depending on the current operating point. For example, the internal combustion engine 100 can be operated in intake manifold injection mode when operating at low engine speed and low load, and it can be operated in direct injection mode when operating at high engine speed and high load. Over a wide operating range, however, it is expedient to operate the internal combustion engine 100 in mixed operation, in which the amount of fuel to be supplied to the combustion chamber 103 is supplied proportionally by intake manifold injection and direct injection.

[0038] Furthermore, a computing unit embodied as a control unit 115 is provided for controlling the internal combustion engine 100. The control unit 115 can operate the internal combustion engine 100 in direct injection, intake manifold injection, or mixed mode.

[0039] Furthermore, the control unit 115 can also record values ​​from a NOx sensor 123.

[0040] The control unit 115 controls both the injection valves in the intake manifold and the injection valves in the cylinders, which specify the amount of fuel supplied to the internal combustion engine. The required amount of fuel is set by a lambda control integrated in the control unit 115, depending on, among other things, the engine load and the required lambda value. The basic setting is preferably made via an adaptable pilot control included in the lambda control. For this purpose, the output signal of the pilot control is added to the output signal of a lambda controller. The pilot control determines the amount of fuel based, among other things, on the engine load. The relationship between the engine load and the specified amount of fuel is preferably stored in a characteristic map in the control unit 115. Due to system drift, the relationship between the engine load and the specified amount of fuel can change.To compensate for this, adaptation cycles are provided as part of a mixture adaptation in which the relationship in the feedforward control is re-learned.

[0041] During mixture adaptation, systematic errors in the fuel-air mixture are corrected using, preferably, adaptation means and adaptation values ​​determined from them. Different types of errors leading to mixture deviations can occur. Errors in determining the amount of air supplied to the internal combustion engine have a multiplicative effect on fuel metering, while errors caused by leakage air influences or a delay in the actuation of the injection valves have an additive effect. Multiplicative errors are particularly noticeable in the medium load range of the internal combustion engine 100, while additive errors dominate at low loads. Accordingly, the adaptation of the fuel metering is carried out according to known methods, with preference given to multiplicative errors in the medium load range and to additive errors in the low load range.Since multiplicative errors also have an effect in low load ranges and additive errors also in medium load ranges, the adaptation is carried out alternately in the two load ranges until a sufficiently stable adaptation of the feedforward control is achieved.

[0042] In particular, the internal combustion engine 100 can be designed as an internal combustion engine with one or more engine blocks. In particular, a separate intake manifold injection valve can be provided in each air supply section for the cylinders. Likewise, each air supply section per engine block can have its own throttle valve for regulating the incoming air flow. Furthermore, the internal combustion engine 100 can comprise multiple exhaust pipes, with a lambda sensor for measuring the air-fuel ratio being provided in each exhaust pipe.

[0043] Preferably, the internal combustion engine 100 is an internal combustion engine with 2, 3, 4, 6 or 8 cylinders.

[0044] The term mixture formation can be understood as the process by which the air-fuel mixture is prepared for the internal combustion engine. This process is crucial for the performance and efficiency of the internal combustion engine. The mixture is created in a specific ratio of air and fuel to ensure optimal combustion. Mixture formation is usually achieved through the use of injection systems that inject the fuel into the airstream. The air-fuel ratio is controlled by various parameters such as throttle position, injection timing, and injection quantity. The mixture formation adaptation process allows the mixture to be tailored to the specific requirements of each cylinder for optimal performance and efficiency.

[0045] Fig.2 shows a functional diagram to illustrate the method. In a first step 500, an enable condition for the method is checked. Approval for the adaptation method is granted when a stationary or quasi-stationary operating mode or operating point is determined for the internal combustion engine 100. A stationary or quasi-stationary operating mode or operating point for the internal combustion engine 100 exists, for example, when a change in speed and / or a change in air mass flow and / or a change in engine torque and / or a change in accelerator pedal position essentially does not change in a predetermined time interval. Advantageously, for the methods presented, it is checked whether there is a slight change in the relative air mass (ratMAir) in a predetermined time interval. If the change in the relative air mass (ratMAir) does not exceed a predefinable threshold value in the time interval, a stationary or quasi-stationary operating mode or operating point can be assumed.A quasi-stationary operating point for the internal combustion engine 100 can be assumed, and approval is granted. A further necessary criterion for the method is that a split factor facSplt lies between one and zero. The split factor specifies the distribution of the injected fuel quantity via the intake manifold and direct injection valves. The advantage of the method compared to known prior art methods is that the diagnosis of the intake manifold and direct injection paths can be carried out while the intake manifold and direct injection are operating simultaneously. Neither path needs to be shut down for the diagnosis (intrusive test). Approval to continue the method in step 510 is therefore granted when a stationary or quasi-stationary operating state is detected.

[0046] The process is then started again in step 500.

[0047] In a step 510, the NOx sensor signal NOx sens determined and stored by a control unit 115.

[0048] The following describes the method for a four-cylinder internal combustion engine. The method is also applicable without restriction to internal combustion engines with more than two cylinders. The internal combustion engine can preferably be a gasoline, diesel, or hydrogen combustion engine. An air-fuel model is stored on control unit 115, which defines a target air-fuel mixture λ. Soll and specifies it for the four cylinders. The air-fuel model determines a relative fuel quantity for each cylinder n and specifies it for each cylinder.

[0049] Starting with the first cylinder n1 of the internal combustion engine, the mixture of the first cylinder n1 is enriched. Before the enrichment, a first relative fuel quantity rk 1,1for the first cylinder n1 is averaged and stored by the control unit.

[0050] During the enrichment process of the mixture for the first cylinder n1, the air-fuel control model regulates the mixtures of the remaining cylinders in such a way that the target air-fuel mixture λ Soll is kept constant across all cylinders n.

[0051] The enrichment of the first cylinder n1 continues until the monitored NOx sensor signal NOx sens a predeterminable NOx limit value S NOx exceeds or reaches.

[0052] The predeterminable NOx limit value S NOx was determined in an application phase for the internal combustion engine and then stored in the control unit 115.

[0053] The determination of the mixture deviation is simple and robust due to the exponential behavior of NOX emissions via lambda in relation to the predefined NOX limit. When the NOX limit is reached, the lambda threshold is also defined. This is determined in a calibration phase for the combustion engine and then stored in the control unit.

[0054] If the NOx sensor signal exceeds NOx sens the predeterminable NOx limit value S NOx a second relative fuel quantity rk 2,1 for the first cylinder n1 is determined and saved.

[0055] In an alternative embodiment, if NOx sensor signal NOx sens the predeterminable NOx limit value S NOxduring the enrichment process, the measurement for the respective cylinder can be aborted. For this purpose, for example, a time or degree of enrichment can be specified until the preset NOx limit value S NOx by the NOx sensor signal NOx sens must be achieved.

[0056] Subsequently, the enrichment of the first cylinder n1 is reversed, as are the changes in the mixtures of the other cylinders, so that the target air-fuel mixture (λ Soll ) is produced by all cylinders n.

[0057] Step 510 is now repeated for each additional cylinder n until a first relative fuel quantity rk 1,n and a second relative fuel quantity rk 2,n have been determined.

[0058] The method then continues in a step 520.

[0059] In a step 520, for each cylinder n a difference Dn between the second relative fuel quantity rk 2,n and the first relative fuel quantity rk 1,n determined.

[0060] Subsequently, an averaged relative fuel quantity rk m depending on the determined differences D n the relative fuel quantities of the n cylinders. This is preferably done by averaging: rkm=∑i=1nDnn with n being the number of cylinders.

[0061] The method then continues in a step 530.

[0062] In a step 530, it is determined for each cylinder n whether the determined differences D n the averaged relative fuel quantity rk m exceed or fall below.

[0063] If the determined difference D n the averaged relative fuel quantity rk mThe mixture is enriched for the respective cylinder n. This is preferably done via the air-fuel control model.

[0064] If the determined difference D n the averaged relative fuel quantity rk m The mixture is leaned for the respective cylinder n. This is preferably done via the air-fuel control model.

[0065] In a special embodiment, the enrichment or leaning of the respective cylinder is adjusted to the value of the averaged relative fuel quantity rk m carried out.

[0066] In an alternative embodiment, the relative fuel quantities can also be converted into air-fuel ratios and the method can be carried out based on these air-fuel ratios.

[0067] The method can then be started again or ended in step 500.

Claims

[1] Method for adapting a mixture formation of an internal combustion engine (10), in particular a hydrogen burner, with several cylinders (n), wherein the internal combustion engine (10) has a NOx sensor (NOx) in an exhaust system, where a NOx sensor signal (NOx sens ) is determined by a control unit (100), Starting with one cylinder (n), the mixture of the respective cylinder (n) is enriched one after the other up to a predeterminable NOx limit value (S NOx ) is carried out, where for each cylinder (n) a first relative fuel quantity (rk 1,n ) is determined before the respective cylinder (n) is enriched, After enrichment, a second relative fuel quantity (rk 2,n ) is determined for the respective cylinder (s) and the enrichment of the respective cylinder (s) is reversed, where for each cylinder (n) a difference (D n ) between the determined second relative fuel quantity (rk 2,n ) and the determined first relative fuel quantity (rk 1,n ) is determined, depending on the differences determined (D n ) an averaged relative fuel quantity (rk m ) is determined, where for each cylinder (n) depending on the determined difference (D n ) and the averaged relative fuel quantity (rk m ) an adaptation of the mixture formation for the internal combustion engine (10) is carried out. [2] Method according to claim 1, characterized by that a release for the adaptation of the mixture formation is granted when a stationary or quasi-stationary operating state exists for the internal combustion engine (10). [3] Method according to claim 1, characterized bythat during the enrichment of one cylinder, the mixture of the others is adjusted in such a way that a target lambda value (λ Soll ) for the internal combustion engine (10) is kept constant. [4] Method according to claim 1, characterized by that if the difference (D n ) the averaged relative fuel quantity (rk m ), the mixture is leaned out for the respective cylinder (n). [5] Method according to claim 1, characterized by that if the difference (D n ) averaged relative fuel quantity (rk m ) a richening of the mixture for the respective cylinder (n) is carried out. [6] Method according to claim 3, characterized by that the leaning of the mixture to the value of the averaged relative fuel quantity (rk m ) is carried out. [7] Method according to claim 4, characterized bythat the enrichment of the mixture is adjusted to the value of the averaged relative fuel quantity (rk m ) is carried out. [8] Method according to claim 1 characterized by that for each cylinder (n) during enrichment the NOx sensor signal (NOx sens,n ) is continuously recorded, and when the NOx sensor signal (NOx sens,n ) a predeterminable NOx limit value (S NOx ), a release for the procedure is granted, and if the NOx sensor signal (NOx sens,n ) the release threshold (S NOx ) the measurement for this cylinder (n) is discarded and the measurement for the next cylinder is continued. [9] Computing unit (115) configured to carry out a method according to any one of the preceding claims. [10] Computer program which causes a computing unit (115) to carry out a method according to one of claims 1 to 9 when executed on the computing unit (115). [11] A machine-readable storage medium having stored thereon a computer program according to claim 10.

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