Determination of relative fuel outgassing from engine oil

Abstract

The invention relates to a method for determining a time-related quantity of a hydrocarbon-based fuel entering the combustion chamber of an internal combustion engine, which escapes in gaseous form from an emulsion of fuel and engine oil that forms over the operating time of the internal combustion engine and enters the combustion chamber as an additional additive relative filling, wherein the time-related quantity is determined from a difference of offsets of a transfer function of the closed chain of the internal combustion engine with a mixture ratio control, determined in each case by means of system identification, between a manufacturing state of the internal combustion engine and a later operating state, wherein the transfer function indicates a relationship between relative fuel content and relative combustion air.

Description

[0001] The invention relates to a method for determining a time-related quantity of a hydrocarbon-based fuel entering the combustion chamber of an internal combustion engine from an emulsion with engine oil.

[0002] Contamination of engine oil with a hydrocarbon-based fuel from an internal combustion engine is virtually unavoidable. During combustion, unevaporated fuel can enter the engine oil, for example, in the film on the cold combustion chamber walls via piston rings that are not fully sealed. The proportion of fuel introduced into the engine oil in this way depends on the engine starting temperature. Unwanted introduction of fuel into the engine oil can also occur due to defects in the internal combustion engine or be intentional.

[0003] Particularly in hybrid vehicles with gasoline engines, low combustion chamber and engine oil temperatures lead to significant fuel ingress into the engine oil. This ingress is largely volatile provided the operating fluids are heated to the appropriate temperatures. However, with increasing electrification of the drive system, the proportion of driving with combustion engines decreases, meaning that the required temperatures are not reached. This can lead to high ingress and dilution rates of the engine oil in a short period of time. Subsequent heating and the resulting discharge of the volatile components into the combustion chamber via the crankcase ventilation system, in an unknown quantity, can lead to undesirable interactions with regard to combustion and the combustion chamber air ratio.

[0004] To calculate the fuel discharge from engine oil, a model value of the engine control system is used in the current technology. This is calculated based on a modeled oil dilution as a ratio of the entered

[0005] The fuel mass is determined relative to the engine oil mass in the crankcase. From this fuel mass in the oil, the expected absolute fuel discharge into the combustion chamber is calculated.

[0006] In this context, DE 10 2014 013 709 A1 relates to a method for determining a dilution of a lubricant of an internal combustion engine, in which at least one dilution value characterizing the dilution is determined using a model as a function of a fuel input into the lubricant, wherein the dilution value is determined using the model as a function of a fuel discharge from the lubricant.

[0007] DE 10 2012 221 507 B3 relates to a method for determining a composition of a fuel in a lubricant which is located in a housing of an internal combustion engine, the method comprising: specifying a composition of a fuel which has at least a first portion of a first fuel component and a second portion of a second fuel component, determining a mass flow of the fuel, with which mass flow the fuel is introduced into the lubricant in an introduction phase or with which mass flow the fuel is discharged from the lubricant in a discharge phase, determining the composition of the mass flow which is composed of a first mass flow of the first fuel component and a second mass flow of the second fuel component,wherein a first mass flow fraction of the first mass flow of the first fuel component and a second mass flow fraction of the second mass flow of the second fuel component are determined based on a) an input parameter in the input phase or a discharge parameter in the discharge phase, and b) the first fraction of the first fuel component and the second fraction of the second fuel component in the fuel.

[0008] DE 10 2004 008 891 A1 relates to a method for operating an internal combustion engine with oil lubrication and electronic injection, wherein a fuel mass flow evaporating from the oil is determined and taken into account when determining a target injection quantity.

[0009] US 5,331,940 A relates to a closed-loop control system for an internal combustion engine with positive crankcase ventilation. According to this control system, the occurrence of blowby gas is detected in response to the variation of the feedback correction coefficient, a product of a transient blowby gas variable and a time-dependent factor is calculated, and a blowby gas recirculation coefficient is modified by this product to obtain a modified blowby gas recirculation coefficient. This modified coefficient is used to calculate a fuel injection amount when significant blowby gas is supplied to the internal combustion engine after engine start-up.

[0010] Due to the extensive and, in part, inherently unknown physical boundary conditions of oil dilution, which represent the difference between fuel discharge and fuel input from or into the engine oil, the model value of the resulting discharge cannot meet current quality standards to warrant further action. The dependence on operating conditions, particularly temperature and pressure conditions in the combustion engine, is typically too large to reliably determine the gaseous transfer of fuel that has previously formed an emulsion with the engine oil, depending on the fuel concentration in the engine oil. Furthermore, adapting the model to specific projects is very complex due to the multitude of boundary conditions.

[0011] The object of the invention is therefore to improve the determination of relative fuel outgassing from engine oil into an engine combustion chamber.

[0012] The invention is based on the features of the independent claims. Advantageous developments and refinements are the subject of the dependent claims.

[0013] A first aspect of the invention relates to a method for determining a time-related quantity of a hydrocarbon-based fuel entering the combustion chamber of an internal combustion engine, which emerges in gaseous form from an emulsion of fuel and engine oil that forms over the operating time of the internal combustion engine and enters the combustion chamber as an additional additive relative charge, wherein the time-related quantity is determined from a difference of offsets between a manufacturing state of the internal combustion engine and a later operating state, wherein the offsets are those of transfer functions of the closed chain of the internal combustion engine, each determined by means of system identification, wherein the internal combustion engine has a mixture ratio control, wherein the transfer function indicates a relationship between relative fuel proportion and relative combustion air.

[0014] The combustion air ratio specifies the ratio of combustion air to fuel, which significantly influences the operating state of an internal combustion engine, including its power in relation to the fuel supply and its exhaust gas parameters. Therefore, a mixture ratio control is used in the prior art to specify and adjust a combustion air ratio (ratio of fuel to combustion air or vice versa), particularly depending on exhaust gas-related target values. One possible disturbance variable that may occur in this process is the fuel component that, after some operation of the internal combustion engine from its initial state of manufacture, can form an emulsion with engine oil. However, at higher engine oil temperatures, it escapes from the engine oil in gaseous form and can at least partially enter the combustion chamber of the internal combustion engine.In such a case, the above-mentioned mixture ratio control will compensate for this disturbance so that the desired target values, particularly with regard to exhaust emissions, are still achieved. This is essentially the functionality of the closed chain, which is defined by the system to be controlled, including the combustion engine. State-of-the-art approaches exist to perform system identification of the closed chain in order to adapt a feedforward control for the combustion air ratio, particularly depending on the manipulated variable based on the control error, in such a way that the control error is minimized as much as possible simply by selecting the correct feedforward control.

[0015] For this purpose, a transfer function, for example a straight line with the parameters offset (typically the intersection point of the straight line with the y-axis of a typical coordinate system) and gradient, is typically identified using individual measured value tuples over different operating points (preferably by means of a parametric system identification, in which, for example, a straight line describing the linear relationship between the measured values ​​with as little error as possible is determined using linear regression).

[0016] Within the scope of the invention, the y-axis intercept of the transfer function in the prior art is neutrally initialized to a straight line through the origin with effect in the controlled system. Another straight line calculated according to the invention with a variable y-axis intercept does not affect the controlled system. This identified transfer function has a different offset, in particular offset of a straight line, in the manufactured state of the internal combustion engine than after a longer mileage of the internal combustion engine. This is related to the fact that after a certain mileage, fuel collects in the oil. With increasing continuous operating time and the associated increase in engine oil temperature, however, it also evaporates again in gaseous form and penetrates the combustion chamber of the internal combustion engine. As additional fuel is introduced, it disrupts the pre-controlled combustion air ratio.

[0017] It is precisely this offset, which changes over the operating time of the internal combustion engine, that is advantageously used according to the invention to identify the time-related quantity of fuel entering the combustion chamber of the internal combustion engine, in particular by applying a linear relationship according to which the difference between the time-shifted offsets is proportional to a quantity of fuel entering the combustion chamber from the engine oil.

[0018] The determination of the offset in the operating state of the internal combustion engine must be deliberately timed during operation of the internal combustion engine insofar as, after a cold start, the temperature of the engine oil and the components of the internal combustion engine increases over several minutes, resulting in a changed rate of fuel ingress into the engine oil and a changed rate of fuel expulsion from the engine oil into the combustion chamber. During a cold start, fuel tends to liquefy in the combustion chamber and enter the engine oil in liquid form. While this effect decreases significantly with increasing temperature of the internal combustion engine, the temperature of the engine oil tends to increase with increasing time, which increases the gaseous expulsion of fuel from the engine oil and the associated entry into the combustion chamber of the internal combustion engine.This typically results in a maximum fuel induction rate into the combustion chamber after sufficiently long operation of the internal combustion engine. The current offset is preferably determined from the identified relationship as explained above at the maximum or, if possible, in the vicinity of this maximum.

[0019] The resulting fuel entry rate into the combustion chamber of the internal combustion engine, which escapes in gaseous form from the emulsion with the engine oil, can be used for a variety of adjustments, particularly to the applied mixture ratio control with the combustion air ratio as the control variable, for example, to adjust the feedforward control of the mixture ratio control. This can thus contribute to a further reduction of undesirable emissions from the internal combustion engine.

[0020] The result is a reliable estimate of the time-related amount of fuel entering the combustion chamber of an internal combustion engine, avoiding the state-of-the-art detour of estimating the fuel mass entering the engine oil. Instead, values ​​from the closed chain, and in particular from the control error-dependent manipulated variable of the aforementioned mixture ratio control, are used to identify the amount of fuel escaping from the engine oil. In particular, the recursive design of the method significantly simplifies modeling and project-specific implementation compared to the current method.

[0021] According to an advantageous embodiment, the offset is determined by system identification in the operating state only when the engine oil temperature is above a predetermined limit value and / or within a predetermined operating time after a cold start of the internal combustion engine.

[0022] According to a further advantageous embodiment, an offset equal to zero is used in the manufacturing state.

[0023] According to a further advantageous embodiment, a straight line with the parameters offset (the above-mentioned intersection point of the straight line with the y-axis of a typical coordinate system) and gradient is used for the transfer function.

[0024] According to a further advantageous embodiment, the straight line indicates a linear relationship between relative fuel proportion and relative combustion air above a base offset.

[0025] According to a further advantageous embodiment, the offset is determined by system identification in the operating state for reference only after a predetermined distance mileage of a vehicle with the combustion engine has been exceeded or after a predetermined operating time of the combustion engine has been exceeded.

[0026] According to a further advantageous embodiment, the offset is determined by system identification during operation, depending on the magnitude of the control variable based on the control error compared to a triggering threshold, as well as taking into account other boundary conditions related to the entry into the combustion chamber. This addresses the increased probability, i.e., suspicion, of increased outgassing.

[0027] Further advantages, features, and details will become apparent from the following description, which—if appropriate, with reference to the drawings—describes at least one embodiment in detail. Identical, similar, and / or functionally equivalent parts are provided with the same reference numerals.

[0028] They show: Fig. 1: Fuel-combustion air ratios set in the manufacturing state and during operation of the internal combustion engine for use in a method according to an embodiment of the invention. Fig. 2: An exemplary temporal change of an identified offset and the relative fuel concentration in the engine oil during operation of the internal combustion engine. Fig. 3: Variances in the relationship between relative combustion air and relative fuel. Fig. 4: Curves changed by entry into the combustion chamber in relation to Fig. 3.

[0029] The representations in the figures are schematic and not to scale.

[0030] Fig. Figure 1 shows the result of a respective system identification. Here, F on the respective horizontal axis at a measuring point represents the relative fuel that is intentionally introduced into the combustion chamber of the internal combustion engine through a designated fuel supply line. The respective vertical axis L represents the relative combustion air associated with the respective measuring point. Thus, each diagram results in numerous measuring points for which an approximate straight line can be formed using linear regression. The offset B describes a base offset that also occurs in the as-manufactured state of the internal combustion engine. Partial diagram (A) describes measuring points for the as-manufactured state, whereas part diagram (B) indicates measuring points for the operating state.If a respective system identification is carried out for both states, it can be seen that in the operating state after a few months of operation of the internal combustion engine, for example, the analogously determined straight line has an offset O compared to the straight line determined in the manufacturing state of the internal combustion engine according to sub-figure (A). This offset O can be linearly converted into a time-related quantity of fuel from the engine oil entering the combustion chamber of the internal combustion engine, so that the influence of fuel from the engine oil on the combustion chamber is known. The time-related quantity relates in particular to a mass of fuel per predetermined time unit. The volatile fuel mass additionally introduced into the combustion chamber from the crankcase is therefore determined as an additional additive relative charge directly recursively from the adaptation values ​​(i.e. the values ​​from the straight lines) and the control intervention of the primary lambda control.

[0031] Fig. Figure 2 shows the course of an offset value of the straight line from the operating state of the internal combustion engine and the determination of the concentration of fuel in engine oil as an emulsion over time t. While FF[%] indicates the percentage of fuel in the crankcase, to which the star-shaped data points belong, dO, with the corresponding circular data points, represents the offset difference between the operating state and the factory state of the internal combustion engine. This shows that during a cold start, the fuel escaping from the emulsion at time zero is also practically zero or very low, since the temperature of the engine oil is very low, thus keeping fuel evaporation from the emulsion to a minimum.At the same time, however, the cold temperatures immediately after a cold start lead to a high level of fuel entering the engine oil, as at low temperatures the fuel tends to be more fluid than at high temperatures and can therefore easily enter the engine oil in liquid form. In the minutes following a cold start, the fuel concentration in the engine oil increases, but then decreases again, as the elevated temperatures, after a certain operating time of the combustion engine, lead to increased evaporation of the fuel from the engine oil. Based on this prior knowledge, system identification for determining the offset in the operating state is preferably carried out in the area of ​​the maximum fuel concentration in the engine oil, if possible, and at least not at the edges of these curves, i.e.during or immediately after a cold start, and not during very long continuous operating times of the combustion engine and the associated high temperature of the engine oil.

[0032] Fig. Figure 3 shows the gradient f0 of a straight line through the origin in the as-manufactured state compared to the gradient f1 of the straight line through the origin after system modifications due to influences on the feedforward control and the controlled system, for example, due to operational component effects, as opposed to the entry into the combustion chamber from outgassing. The vertical axis L represents the relative combustion air, while F on the respective horizontal axis represents the relative fuel. In parallel, the determined gradients fh0 and fh1 represent the analog transfer functions with y-axis intercept.

[0033] Fig.4 shows the changed gradient f2b of the origin line resulting from the entry into the combustion chamber as well as the gradient fh2b and y-axis intercept oh2b of the analog transfer function, where f2b < f1 and oh2b < 0 are found, indicating outgassing.

[0034] Although the invention has been illustrated and explained in detail by preferred embodiments, the invention is not limited by the disclosed examples, and other variations may be derived therefrom by those skilled in the art without departing from the scope of the invention. It is therefore clear that a multitude of variations exist. It is also clear that exemplary embodiments are truly only examples and should not be construed as limiting the scope, possible applications, or configuration of the invention in any way.Rather, the preceding description and the description of the figures enable the person skilled in the art to implement the exemplary embodiments in concrete terms, whereby the person skilled in the art, with knowledge of the disclosed inventive concept, can make various changes, for example with regard to the function or the arrangement of individual elements mentioned in an exemplary embodiment, without departing from the scope of protection defined by the claims and their legal equivalents, such as further explanations in the description.

Claims

[1] Method for determining a time-related quantity of a hydrocarbon-based fuel entering the combustion chamber of an internal combustion engine, which emerges in gaseous form from an emulsion of fuel and engine oil which forms over the operating time of the internal combustion engine and enters the combustion chamber as an additional additive relative filling, wherein the time-related quantity is determined from a difference of offsets between a manufacturing state of the internal combustion engine and a later operating state, wherein the offsets are those of transfer functions of the closed chain of the internal combustion engine which are each determined by means of system identification, wherein the internal combustion engine has a mixture ratio control, wherein the transfer function indicates a relationship between relative fuel proportion and relative combustion air. [2] Method according to claim 1, wherein the offset is determined by system identification in the operating state only at an engine oil temperature above a predetermined limit value and / or within a predetermined operating time after a cold start of the internal combustion engine. [3] Method according to claim 1, wherein the offset is determined by system identification in the operating state as a function of the amount of the manipulated variable based on the control error in comparison to a triggering threshold value and taking into account further boundary conditions related to the entry into the combustion chamber. [4] A method according to any one of the preceding claims, wherein an as-manufactured offset equal to zero is used. [5] Method according to one of the preceding claims, wherein a straight line with the parameters offset and slope is used for the transfer function. [6] Method according to claim 5, wherein the straight line indicates a linear relationship between relative fuel proportion and relative combustion air above a base offset. [7] Method according to one of the preceding claims, wherein the offset is determined by system identification in the operating state only after a predetermined distance mileage of a vehicle with the internal combustion engine has been exceeded or after a predetermined operating time of the internal combustion engine has been exceeded. [8] Method according to one of the preceding claims, wherein the relative fuel input is determined by comparing the offsets by system identification in the operating state.

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