DE102009045419A1 - Determining composition of fuel mixture, e.g. gasoline and ethanol, involves combining weighting factor with composition values derived from engine parameters - Google Patents

Abstract

A first composition value (12) is established from a first engine parameter, at least one additional composition value (13-15) is determined from at least one other parameter and a weighting factor (18) for these values which depends on their estimated accuracy is specified. The composition of the fuel mixture is then calculated on the basis of the weighted combination of these two values. The mixture comprises two or more fuels with different chemical, physical and/or combustion properties. Parameters for different engine operating conditions are established, which are dependent upon these properties.

Description

The invention relates to a method for determining the composition of a fuel mixture of a first fuel and at least a second fuel for operating an internal combustion engine, wherein the fuels differ in their chemical and / or physical and / or combustion properties, wherein operating ranges of the internal combustion engine delimited from each other and wherein characteristics are determined, which depend on the chemical and / or physical and / or combustion properties of the fuel mixture.

The invention further relates to a device for determining the composition of a fuel mixture of a first fuel and at least a second fuel for operating an internal combustion engine, wherein the fuels differ in their chemical and / or physical and / or combustion properties, wherein operating ranges of the internal combustion engine from each other are delimited, wherein parameters are determined, which depend on the chemical and / or physical and / or combustion properties of the fuel mixture and wherein the internal combustion engine is assigned a control unit.

State of the art

Internal combustion engines based on gasoline engines are generally operated with a fuel from hydrocarbons from fossil fuels based on refined crude oil. To this fuel is increasingly from renewable raw materials (plants) produced alcohol, such as ethanol or methanol, mixed in different mixing ratios. In the US and in Europe, a mixture of 75-85% ethanol and 15-25% gasoline is often used under the brand name E85. The internal combustion engines are designed so that they can be operated with both pure gasoline and with mixtures up to E85; this is called "flex-fuel operation". For economical operation with low pollutant emissions coupled with high engine performance, the operating parameters in flex-fuel operation must be adapted to the particular fuel mixture present. By way of example, there is a stoichiometric air / fuel ratio at 14.7 parts by weight of air per part of gasoline, but when using ethanol, an air content of 9 parts by weight must be set.

In flex-fuel operation, an adapted enrichment factor must be specified as a function of the mixing ratio due to the different temperature-dependent evaporation properties of ethanol and gasoline at the start of the internal combustion engine. The ignition timing must also be adjusted depending on the fuel mixture. The knowledge of the present fuel mixture ratio is therefore of fundamental importance for the operation of the internal combustion engine.

To determine the composition of the fuel mixture, different fuel type sensors, also referred to as "fuel composition sensors" can be used. Fuel type sensors use the different properties of the fuels used, for example, alcohol and gasoline, to determine the fuel composition. For example, ethanol is a protic solvent which contains hydrogen ions and has a large dielectric constant, which is dependent on the water content. Gasoline is an aprotic solvent with a small dielectric constant. Based on this, there are fuel type sensors which determine the fuel composition based on the dielectric properties of the fuel mixture. Other fuel type sensors utilize the different electrical conductivity or different optical properties of the fuels, such as, for example, the different refractive indices. The disadvantage here is that the system costs are increased by the use of fuel type sensors. Another disadvantage is that according to existing regulations, the correct functionality of the fuel type sensors must be monitored, which requires additional effort.

Therefore, software-based systems for determining fuel composition have been developed which do not use special fuel type sensors but which evaluate the signals of the sensors present on the internal combustion engine. These systems can be realized more cost effectively than systems with fuel type sensors.

From the DE 3036107 C3 a control device is known for a Kraftstoffzumesssystem in an internal combustion engine consisting of a fuel supply device (fuel injection valve), a lambda probe, means (timer) for forming a Grundzumesssignals the operating characteristic variable dependent ultimately determines the drive signal (ti) of the fuel supply device, a lambda controller, the starting from a signal measured by the lambda probe (λ) determines a correction factor which multiplicatively affects the Grundzumesssignal (tp) with the correction factor. It is provided that the lambda correction is dependent not only on the correction factor (KR λ) but also on an additive (KA λ) and / or a multiplicative (KL λ) correction variable which is determined as a function of the correction factor and operating parameters.

The control device makes it possible to compensate for systematic deviations of the fuel metering, which is specified by the basic metering signal, ie the so-called pilot control, from the value determined by the lambda control by an adaptation intervention with a corresponding long-term correction. Systematic deviations can be caused, for example, by aging influences or by manufacturing influences. On average, the amount of fuel defined by the corrected precontrol corresponds to the quantity actually required. Short-term deviations can be compensated with the lambda controller, to which the entire control range is now available again. The underlying process is also known as mixture adaptation.

The determination of the fuel mixture ratio can be carried out without additional fuel-type sensor by means of a fuel adaptation. The fuel adaptation is activated after a refueling detected by the tank level sensor. A fuel composition changed by refueling results in a changed stoichiometric air / fuel ratio. By a corresponding intervention of the lambda control on the operating parameters of the internal combustion engine, in particular on the set air / fuel ratio and the ignition timing, this change in the fuel properties is taken into account in the context of fuel adaptation. From the intervention of the lambda control or the fuel adaptation can be concluded that the stoichiometric ratio and hence the composition of the fuel mixture. The composition of the fuel mixture can be determined inexpensively by a pure software solution accordingly.

The disadvantage here is that after a refueling process during the fuel adaptation, the mixture adaptation must be temporarily deactivated so that changed combustion properties of the fuel mixture are not erroneously compensated by the long-term correction of the mixture adaptation. The deactivation of the mixture adaptation is undesirable and contradicts the requirements of CARB in the USA in particular for continuous monitoring and diagnosis of the fuel supply system.

Another disadvantage of the method is that in a refueling operation with small amounts of fuel, the tank level sensors do not always reliably recognize this. If such minute amounts of refueling are repeatedly carried out, it may happen, in particular with a low filling level of the fuel tank, that the fuel composition changes significantly, without this being recognized and compensated by the fuel adaptation. The change in combustion characteristics is then erroneously corrected by the mixture adaptation.

Another system for determining the fuel mixture ratio without using a specific type of fuel sensor is described in applicant's unpublished document R.312407. The document describes a method for determining the ratio (z) of constituents of a fuel mixture which is conveyed by a fuel pump, the method being characterized in that a measure (p_KP) of the power consumption of the fuel pump is detected and that on the basis of the detected measure (p_KP) the ratio (z) of components of the fuel mixture is determined.

Another method for determining the fuel mixture ratio without using a specific fuel type sensor is described in applicant's unpublished document R.318835. The document describes a method for determining the composition of a fuel mixture of a first fuel and a second fuel for operating an internal combustion engine, wherein the first and the second fuel have different octane numbers and wherein the internal combustion engine has at least one knock sensor and a knock control. The method is characterized in that the composition of the fuel mixture is determined by means of an output signal of the knock sensor.

Another method for determining the composition of a fuel mixture of a first and at least a second fuel for operating an internal combustion engine, wherein fuel mixtures of different composition have a different knock resistance, characterized in that the composition of the fuel mixture is determined from the ignition angle, in which just no Engine knock occurs. The method is described in the not yet published document R.320246 of the applicant.

In the not yet published document R.325571 the applicant is a method for determining a fuel composition of a fuel mixture of a first and at least a second fuel for operating an internal combustion engine with known air-fuel ratio or a lambda value at known fuel, in which by Interventions the smoothness of the internal combustion engine is at least temporarily negatively affected, the method being characterized in that the influence by means of a variation of an ignition angle and / or by means of a variation of the air-fuel ratio is carried out, are derived from a resulting uneven or from a resulting gradient for the rough running a parameter for the composition of the currently existing fuel mixture or a lambda value for the cylinders of the internal combustion engine.

In the applicant's unpublished document R.322638, a method is described for determining the composition of a fuel mixture comprising a first fuel and at least one second fuel for operating a self-igniting internal combustion engine with at least one sensor determining the course of the combustion in at least one cylinder of the internal combustion engine characterized in that a measure of the stability of the combustion process is formed from a variable characterizing a combustion process in at least one cylinder of the internal combustion engine and that the determination of the composition of the fuel mixture is based on the measure of the stability of the combustion process.

In the not yet published document R.327499 the applicant is a method for determining a fuel composition of a fuel mixture of a first and at least a second fuel for operating an internal combustion engine, wherein a control unit, an output signal of a arranged in an exhaust passage of the internal combustion engine broadband lambda probe is supplied , which is characterized in that the composition of the fuel mixture from the course of a pump current characteristic of the broadband lambda probe in dependence on the lambda value of the exhaust gas is determined.

The mentioned methods for determining the composition of a fuel mixture based on various, the internal combustion engine or its control unit already present characteristics and signals have the disadvantage that the achievable uncertainty in the determination of the fuel composition is sometimes significantly greater than the accuracy required to control the internal combustion engine.

In the applicant's unpublished publication R.322094 a method for controlling an internal combustion engine is described, which is operated with a fuel mixture of a first and at least a second fuel, wherein the internal combustion engine, a fuel metering device, a tank level gauge for determining the tank contents and a change of the tank contents, a sensor for detecting the cylinder charge for determining an internal combustion engine supplied air mass and at least one exhaust gas probe for determining and controlling the oxygen content in the exhaust gas, wherein the method is characterized in that in a first process step, a first value for the composition the fuel mixture is determined from the supplied air mass and the measured change in the tank contents, taking into account the oxygen content in the exhaust gas, that in a second process step, a second value for the composition the fuel mixture is determined from the air mass supplied during idling of the internal combustion engine and the amount of fuel supplied by means of the fuel metering device, the first and the second value are compared for agreement within a predetermined limit, and in the case of differing values, an error in the fuel Dosing device, in the determination of the supplied air mass or the tank level gauge is closed. The method therefore serves to monitor the fuel metering device, to monitor the supplied air mass or to monitor the tank level gauge; the accuracy in determining the two values for the composition of the fuel mixture is limited to the accuracy of the individual underlying methods for determining the composition and thus subjected to great statement blurring.

It is an object of the invention to provide a method which allows a reliable and cost-effective detection of the composition of a fuel mixture of at least two fuels with a sufficiently low statement uncertainty.

Disclosure of the invention

The object of the invention relating to the method is achieved by determining a first composition value of the fuel mixture from at least one second parameter determining at least one second composition value that predetermines weighting factors for the composition values as a function of the statement accuracy of the respective composition value and that the composition of the fuel mixture is determined from a combination of the first composition value and at least the second composition value, weighted with the associated weighting factors.

The different properties of the pure fuels result in different chemical and physical properties as well as different combustion properties for mixed fuel mixtures in different mixing ratios. These properties affect several, mostly from each other independent, parameters that are detected to control the internal combustion engine. Thus, indicia for the composition of the fuel mixture in the form of composition values can be derived from the individual parameters. A composition value describes the composition of the fuel mixture as determined by a characteristic. Depending on the correlation of the underlying parameter with the composition of the fuel mixture and tolerances in the determination of the underlying measured values, the individual composition values have information blurring that can be significantly higher than the desired accuracy in determining the composition of the fuel mixture. Since the individual parameters are independent of one another, a stochastic distribution of the composition values derived therefrom and the associated statement blurring can be assumed. By a suitable combination of the individual composition values, therefore, the actual composition of the fuel mixture can be determined much more accurately than is possible based on the individual composition values. An increased number of available composition values increases the accuracy of the reading.

The composition values can be derived from sensor signals or from calculated values in the program sequence of a control of the internal combustion engine. Therefore, different composition values can be determined with different accuracy. According to the invention, therefore, it is provided to provide the composition values in the determination of the composition of the fuel mixture with weighting factors which reflect the respective measurement accuracy. This reduces the deviation of the particular composition from the real value. Furthermore, the size of the expected mean deviation can be determined more accurately.

It is advantageous in the method that the determination of the composition values and thus of the composition of the fuel mixture can take place from parameters already present in modern internal combustion engines. There are no additional components, such as additional fuel-type sensors, can be provided, which allows a cost-effective implementation of the method as a pure software solution.

In order to carry out the method according to the invention, diagnostic functions required by the legislator, such as, for example, the mixture adaptation, do not have to be deactivated, as a result of which the acceptance of the method significantly increases compared to existing software solutions.

Another advantage over existing solutions is that the determination of the fuel composition is not tied to the recognition of a refueling operation. If, in existing processes which require the detection of a refueling operation, small quantities which are no longer detectable by the tank leveling system are frequently refueled, this can lead to a noticeable change in the composition of the fuel mixture, in particular if the tank is at a low level, without this being the case is recognized.

In different operating ranges of the internal combustion engine such as idling, thrust operation, partial and full-load operation, the composition values can be determined with different accuracy. According to the invention, it is therefore provided that the weighting factors of the individual composition values are predefined as a function of the present operating range of the internal combustion engine. In this case, it may also be provided that in an operating range a weighting factor for a composition value is equal to zero and this compositional value is not taken into account in the determination of the composition. In this embodiment, the composition of the fuel mixture can be determined with improved accuracy in a wide range of applications of the internal combustion engine.

If the weighting factors are determined from the reciprocal of the percentage accuracy of the composition value, the Gaussian error propagation method can be used to calculate the most likely composition of the fuel mixture and the mean deviation from the true value. If the statement accuracy is 20% by way of example, the weighting factor 1 / 0.2 = 5 must be used. In the case of two composition values Z1 and Z2 and two weighting factors W1 and W2, the most probable composition is wZ wZ = (W1 ² · Z1 + W2 ² · Z2) / (W1 ² + W2 ² ).

The accuracy m for the most probable composition wZ for a maximum ethanol content of 85% is calculated as m = 85% / √ W1² + W2²

The composition of a fuel mixture may be determined from a predetermined number of composition values by determining the composition of the fuel mixture from the sum of the composition values multiplied by the squares of the associated weighting factors divided by the sum of the squares of the weighting factors. To This calculation according to the method of Gaussian error propagation determines the most probable value for the composition. An increase in the number of composition values advantageously reduces the deviation from the true value of the composition and improves the error limits in the determination.

A particularly simple specification of the weighting factors for different operating ranges and a simple calculation with sufficient accuracy are achieved by specifying the weighting factors in stages.

The achievable accuracy of the true composition estimate can be calculated by dividing the maximum ethanol content by the square root of the sum of the squares of weighting factors. With an ethanol content of 85% maximum and a relative mean deviation of 10%, the absolute mean deviation is thus 8.5%.

Modern internal combustion engines often have knock sensors whose output signal is used for knock control. If fuels differ in their octane number or in their anti-knock properties, the octane number and the anti-knocking properties of a fuel mixture derived therefrom are determined by the mixing ratio of the fuels involved. From the output signal of the knock sensor or a control operation of the knock control, for example the Zündwinkelausgabe, so regardless of other methods for determining composition values on the composition of the fuel mixture can be concluded. It can therefore be provided that one of the parameters for determining one of the composition values of the fuel mixture is determined from an output signal of a knock sensor or from a knock control of the internal combustion engine and that at least one weighting factor for the composition value is predefined as a function of the achieved accuracy of the thus determined composition value. Depending on the number of distinguishable operating ranges, a plurality of weighting factors may be specified for the composition value thus determined.

A further composition value can be determined by using the rotational speed of an electronically commutated fuel pump or the electric pump supplied to the fuel pump as parameters for determining one of the composition values of the fuel mixture, and at least one weighting factor for the fuel quantity determined in accordance with the achieved accuracy of the composition value thus determined Composition value is specified. The physical distinguishing feature between the mixed fuels here is the different viscosity and the different temperature dependence of the viscosity of the individual fuels and thus of the resulting fuel mixture. The viscosity of the fuel mixture directly influences the speed and the electrical current supplied to the fuel pump, so that indicia for the composition of the fuel mixture can be obtained from these characteristics. It is advantageous here that the determination of the composition value takes place independently of other methods for determining parameters from which further composition values are derived, which is a prerequisite for a stochastic distribution of the composition values.

According to a preferred embodiment variant of the invention, it can be provided that one of the parameters for determining one of the composition values of the fuel mixture is determined by lowering a prefeed pressure established by a low-pressure fuel pump until vapor bubbles exist in the region between the low-pressure fuel pump and a high-pressure fuel pump arranged thereafter occur that is used as a parameter of the prefeed pressure, from which vapor bubbles occur and that at least one weighting factor for the composition value is given depending on the achieved accuracy of the thus determined composition value. The method can be used in particular for directly injecting internal combustion engines. The basis for this is the different vapor pressure of the fuels used. Thus, for example, shows a fuel mixture of ethanol and gasoline at constant temperature and an ethanol content of greater than 30% with increasing content of ethanol a decreasing vapor pressure. If, for example, during a test function, the prefeed pressure of the low-pressure fuel pump is temporarily lowered so far that vapor bubbles form in the fuel mixture between the low-pressure fuel pump and the high-pressure fuel pump as a result of falling below the vapor pressure of the fuel mixture, then the high-pressure delivery collapses. If the temperature is known, it is now possible to deduce the composition of the fuel mixture from the pre-feed pressure set.

Fuels differ in their energy density. Accordingly, the energy density of a fuel mixture depends on the mixing ratio and the respective energy densities of the fuels used. The power consumption of an internal combustion engine at idle is known as a function of coolant temperature, efficiency, ignition angle and secondary consumers such as air compressor, generator, coolant pump, oil pump and speed or determinable. In a fuel with a low energy density more fuel must be supplied at idle compared to a fuel with high energy density of the internal combustion engine. Accordingly, the amount of fuel supplied to the internal combustion engine during idling is directly related to the mixing ratio of the fuel mixture and can be used as a parameter for determining a composition value. Therefore, it can be provided that the consumption of fuel mixture during idling is used as a parameter for determining one of the composition values of the fuel mixture, and that at least one weighting factor for the composition value is predefined as a function of the achieved accuracy of the composition value determined in this way. It is advantageous in this case that the fuel volume flow supplied to the internal combustion engine during idling is present to the control unit as a parameter over the duration of the injection.

An emaciation of the air-fuel mixture, d. H. an increase in the lambda value leads to an increasing uneven running in internal combustion engines. Different fuels and fuel mixtures composed thereof have a typical so-called lean running limit and continue to limit the amount of exhaust gas that can be returned in an exhaust gas recirculation. If the internal combustion engine supplied air-fuel mixture emaciated, so both the ignition delay is increased and the ignition slowed down or the ignition is not at all. This leads to extremely delayed burns or combustion misfires, which then result in a significantly increased uneven running. The knowledge of the lean running limit and the limit for the exhaust gas recirculation are an indication of the mixing ratio of the fuel mixture used. It can therefore be provided that a lean running limit and / or a limit of the exhaust gas recirculation compatibility is used as the parameter for determining one of the composition values of the fuel mixture and that at least one weighting factor for the composition value is predefined depending on the achieved accuracy of the composition value determined in this way. The advantage here is that the lean-burn limit and Abgasrückführverträglichkeit can be easily determined by a corresponding variation of the air-fuel ratio or the recirculated exhaust gas amount. An altered combustion stochastics can be determined by evaluating the crankshaft speed, for example by means of corresponding rest rest algorithms.

It is provided that the profile of a pumping current of a broadband lambda probe arranged in the exhaust gas of the internal combustion engine is used as a parameter for determining one of the composition values of the fuel mixture, depending on the lambda value of the exhaust gas and at least one depending on the achieved accuracy of the composition value determined in this way Given a weighting factor for the composition value, it is possible to use a further independently determined composition value to determine the composition of the fuel mixture. Exhaust gases from different fuels, such as ethanol and gasoline, are characterized by different hydrogen-carbon monoxide ratios. The exhaust gas of ethanol of an ethanol-containing fuel mixture has a higher hydrogen-carbon monoxide ratio than occurs in the combustion of pure gasoline. As a result of the changed gas mixture, the characteristic curve of the broadband lambda probe, in particular in a region lambda <1, shows a pump current behavior which is dependent on the mixing ratio of the fuels used. The advantage here is that can be used to determine the composition value of an existing broadband lambda probe and no other components are needed, so that only a corresponding software adaptation in the control unit of the internal combustion engine is necessary.

Without additional components, a compositional value may be determined by deriving one of the characteristics for determining one of the compositional values of the fuel mixture from a draft tube wall thickness and specifying at least one weighting factor for the compositional value depending on the achieved accuracy of the compositional value thus determined. In internal combustion engines with intake manifold injection, a Saugrohrwandfilm forms from the respective fuel or from the respective fuel mixture. The thickness of the Saugrohrwandfilms depends on the enthalpy of enthalpy of the fuel used. Since fuels, such as gasoline and ethanol, differ in their enthalpy of vaporization, the Saugrohrwandfilmstärke depends directly on the mixing ratio of the fuels used. In the case of a change in the air / fuel ratio caused by a driver request or the engine control, the intake tube wall film must first be built up or taken down to the new equilibrium strength. The compositional value can therefore be determined by observing the lambda engagement in the transition from a fuel cut to resume fueling and combustion.

A further embodiment of the invention provides that one of the parameters for determining one of the composition values of the Fuel mixture is determined from the control of the mixture adaptation and that depending on the achieved accuracy of the thus determined composition value at least one weighting factor for the composition value is specified. The combustion properties of fuel mixtures are directly dependent on the particular composition of the fuel mixture. Due to the lambda-controlled mixture adaptation, the operating parameters of the internal combustion engine are adapted to a changed fuel composition in such a way that the exhaust gas composition lies within the prescribed range, for example at a lambda = 1. From the passive observation of the mixture adaptation, that is to say without an intervention in the diagnostic procedure or a blocking of the mixture adaptation in a fuel supply diagnosis, a further indication of the composition of the fuel mixture and thus a further composition value can be obtained.

A further composition value of the fuel mixture can be independently determined by using a signal of a fuel type sensor as the parameter for determining one of the composition values of the fuel mixture and at least one weighting factor for the composition value being predetermined depending on the achieved accuracy of the composition value thus determined.

The device-related object of the invention is achieved in that the control unit characteristic quantities and / or signals are supplied for determining the characteristics, that in the control unit a program sequence for determining at least two composition values from the characteristics is provided that weighting factors in dependence on The accuracy of the composition values in the respective operating ranges is predefined and that a program sequence for determining the composition of the fuel mixture from the at least two composition values and the associated weighting factors is provided in the control unit. The composition of a fuel mixture can thus be determined by a pure software solution without additional components without having to temporarily deactivate diagnostic functions specified by the legislator. The number of compositional values taken into account for determining the composition of the fuel mixture may be increased in accordance with the number of signals and characteristics that are dependent on the characteristics of the fuel mixture, which may reduce the uncertainty of the identified composition of the fuel mixture.

The method and apparatus may preferably be used to determine the composition of a fuel mixture of gasoline and alcohol, preferably a fuel mixture of gasoline and ethanol.

Short description of the drawing

The invention will be explained below with reference to an embodiment shown in the figure. It shows:

1 a diagram for determining a composition of a fuel mixture.

1 shows a diagram for determining a composition 10 a multi-fuel mixture for the composition 10 characteristic parameters using the example of a gasoline-ethanol fuel mixture. Along a first axis 11 the percentage of ethanol in the fuel mixture is plotted. To a desired total deviation 16 in determining the composition 10 to reach out to be for the composition 10 characteristic characteristics a first composition value 12 , a second composition value 13 , a third composition value 14 and a fourth composition value 15 certainly. The composition values 12 . 13 . 14 . 15 are shown as expected with standard deviation and along a second axis 17 arranged side by side. The composition values 12 . 13 . 14 . 15 can be determined as an example of an octane number, a vapor pressure of the fuel mixture, a lean running limit or a knock resistance as characteristic parameters. Instead of four values, it is also possible according to the invention to use a different number of two or more than two composition values. The standard deviation of the composition values 12 . 13 . 14 . 15 can be greater than the desired maximum total deviation 16 for the determination of the composition 10 be of the fuel mixture.

According to the invention, the composition 10 of the fuel mixture by a combination of the compositional values 12 . 13 . 14 . 15 certainly. The combination is done by forming a weighted average over the compositional values 12 . 13 . 14 . 15 , The composition values 12 . 13 . 14 . 15 are weighting factors 18 which is a measure of the accuracy of the respective composition value 12 . 13 . 14 . 15 are. By way of example, a weighting factor expresses 18 with the value 5 an accuracy of 1/5 = 20%; in weighting factor 18 with the value 4 means an accuracy of 1/4 = 25%.

Because the composition values 12 . 13 . 14 . 15 were determined independently of each other and thus by a stochastic distribution of the composition values 12 . 13 . 14 . 15 about the composition 10 can be assumed, the required and by the total deviation 16 illustrated accuracy in determining the composition 10 of the fuel mixture, even if the statement blurs the underlying compositional values 12 . 13 . 14 . 15 are significantly larger.

With an increasing number of considered composition values 12 . 13 . 14 . 15 the weighted average formed approximates the actual composition 10 and thus the true ethanol content of the fuel mixture and the error in determining the composition 10 decreases.

The improvement of the statement accuracy by the use of the weighted averaging is explained in the following with an example calculation:
The first composition value 12 40%, the second composition value 13 amount to 20%. The weighting factors 18 , which represent the measurement deviation in the determination of the respective parameter are 5 and 3, respectively. According to the known method of Gaussian error analysis, the composition determined on the basis of the above two value pairs 10 :
composition 10 = (40% · 5 ² + 20% · 3 ² ) / (5 ² + 3 ² ) = 34.7%

Likewise, the method of Gaussian error analysis allows the accuracy in the determination of the composition 10 at the two weighting factors 18 with the values 5 and 3 and a maximum ethanol content of 85%: 85% / √ 5² + 3² = 14.6%

The combination of the two composition values 12 . 13 with weighting factors 18 with the values 5 and 3, which correspond to accuracies of 85% / 5 = 17% and 85% / 3 = 28.3% respectively, gives a statement with an improved accuracy of 14.6%.

For an arbitrary number n of composition values Zi with weighting factors Wi, the ethanol content and the achievable accuracy at a maximum ethanol content Emax can be calculated as follows:

According to the invention, the weighting factors 18 be determined depending on the operating condition of the internal combustion engine. This improves the reliability of the method and its accuracy, since in some operating conditions characteristics can be determined very accurately and therefore can be highly weighted. On the other hand, it may also be provided to weight a parameter with the factor "zero" in a specific operating state and thus not to take it into consideration.

Because the individual composition values 12 . 13 . 14 . 15 By a control unit of the internal combustion engine already present characteristics and sensor signals can be determined, the determination of the composition 10 the fuel mixture done by a pure software extension in the control unit, without additional components and sensors must be provided. To determine the compositional values 12 . 13 . 14 . 15 and the composition 10 No diagnostic routines, such as the mixture adaptation, must be interrupted.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 3036107 C3 [0007]

Claims (17)

Method for determining the composition ( 10 ) of a fuel mixture of a first fuel and at least a second fuel for operating an internal combustion engine, wherein the fuels differ in their chemical and / or physical and / or combustion properties, wherein operating ranges of the internal combustion engine are delimited from each other and wherein characteristics are determined, which depend on the chemical and / or physical and / or combustion properties of the fuel mixture, characterized in that from a first parameter a first composition value ( 12 ) of the fuel mixture is determined that from at least one second parameter at least a second composition value ( 13 ), it is determined that weighting factors ( 18 ) for the composition values ( 12 . 13 ) are given as a function of the accuracy of the respective compositional value and that the composition ( 10 ) of the fuel mixture from one with the associated weighting factors ( 18 ) weighted combination of the first composition value ( 12 ) and at least the second composition value ( 13 ) is determined. Method according to claim 1, characterized in that the weighting factors ( 18 ) of the individual composition values ( 12 . 13 ) as a function of the present operating range of the internal combustion engine. Method according to claim 1 or 2, characterized in that the weighting factors ( 18 ) are determined from the reciprocal of the percentage accuracy of the composition value. Method according to one of claims 1 to 3, characterized in that the composition ( 10 ) of the fuel mixture from the sum of the with the squares of the associated weighting factors ( 18 ) multiplied composition values ( 12 . 13 ) divided by the sum of the squares of the weighting factors ( 18 ) is determined. Method according to one of claims 1 to 4, characterized in that the weighting factors ( 18 ) in steps. Method according to one of claims 1 to 5, characterized in that the achievable accuracy of the estimate of the true composition is calculated by dividing the maximum ethanol content by the square root of the sum of the squares of the measurement inaccuracies divided by the squares of the number of compositional values considered. Method according to one of claims 1 to 6, characterized in that one of the parameters for determining one of the composition values ( 12 . 13 . 14 . 15 ) of the fuel mixture is determined from an output signal of a knock sensor or from a knock control of the internal combustion engine and that, depending on the achieved accuracy of the thus determined composition value, at least one weighting factor ( 18 ) for the composition value ( 12 . 13 . 14 . 15 ) is given. Method according to one of claims 1 to 7, characterized in that as parameters for determining one of the composition values ( 12 . 13 . 14 . 15 ) of the fuel mixture, the rotational speed of an electronically commutated fuel pump or the electric pump supplied electric power is used and that depending on the achieved accuracy of the thus determined composition value at least one weighting factor ( 18 ) for the composition value ( 12 . 13 . 14 . 15 ) is given. Method according to one of claims 1 to 8, characterized in that one of the parameters for determining one of the composition values ( 12 . 13 . 14 . 15 ) of the fuel mixture is determined by lowering a prefeed pressure established by a low-pressure fuel pump until vapor bubbles occur in the region between the low-pressure fuel pump and a high-pressure fuel pump arranged thereafter, the prefeed pressure is used as the characteristic value from which vapor bubbles occur and depending on the achieved accuracy of the thus determined composition value at least one weighting factor ( 18 ) for the composition value ( 12 . 13 . 14 . 15 ) is given. Method according to one of claims 1 to 9, characterized in that as a parameter for determining one of the composition values ( 12 . 13 . 14 . 15 ) of the fuel mixture, the consumption of fuel mixture is used at idle and that depending on the achieved accuracy of the thus determined composition value at least one Weighting factor ( 18 ) for the composition value ( 12 . 13 . 14 . 15 ) is given. Method according to one of claims 1 to 10, characterized in that as a parameter for determining one of the composition values ( 12 . 13 . 14 . 15 ) of the fuel mixture a lean running limit and / or a limit of Abgasrückführverträglichkeit is used and that depending on the achieved accuracy of the thus determined composition value at least one weighting factor ( 18 ) for the composition value ( 12 . 13 . 14 . 15 ) is given. Method according to one of claims 1 to 11, characterized in that as a parameter for determining one of the composition values ( 12 . 13 . 14 . 15 ) of the fuel mixture the course of a pumping current of a arranged in the exhaust gas of the internal combustion engine broadband lambda probe is used as a function of the lambda value of the exhaust gas and that depending on the achieved accuracy of the thus determined composition value at least one weighting factor ( 18 ) for the composition value ( 12 . 13 . 14 . 15 ) is given. Method according to one of claims 1 to 12, characterized in that one of the parameters for determining one of the composition values ( 12 . 13 . 14 . 15 ) of the fuel mixture is derived from a Saugrohrwandfilmstärke and that at least one weighting factor (depending on the achieved accuracy of the thus determined composition value ( 18 ) for the composition value ( 12 . 13 . 14 . 15 ) is given. Method according to one of claims 1 to 13, characterized in that one of the parameters for determining one of the composition values ( 12 . 13 . 14 . 15 ) of the fuel mixture is determined from the regulation of the mixture adaptation and that, depending on the achieved accuracy of the thus determined composition value, at least one weighting factor ( 18 ) for the composition value ( 12 . 13 . 14 . 15 ) is given. Method according to one of claims 1 to 14, characterized in that as a parameter for determining one of the composition values ( 12 . 13 . 14 . 15 ) of the fuel mixture, a signal of an ethanol sensor is used and that, depending on the achieved accuracy of the thus determined composition value at least one weighting factor ( 18 ) for the composition value ( 12 . 13 . 14 . 15 ) is given. Device for determining composition ( 10 ) of a fuel mixture of a first fuel and at least a second fuel for operating an internal combustion engine, wherein the fuels differ in their chemical and / or physical and / or combustion properties, wherein operating ranges of the internal combustion engine are separated from each other, wherein characteristics are determined, which depend on the chemical and / or physical and / or combustion properties of the fuel mixture and the internal combustion engine is assigned a control unit, characterized in that the control unit characteristics and / or signals are supplied to determine the characteristics that in the control unit a program flow for Determination of at least two composition values ( 12 . 13 . 14 . 15 ) is provided from the characteristics that weighting factors ( 18 ) are predetermined as a function of the accuracy of the composition values in the respective operating ranges, and in the control unit a program sequence for determining the composition of the fuel mixture from the at least two composition values and the associated weighting factors ( 18 ) is provided. Use of the method or device according to one of the preceding claims for determining the composition ( 10 ) of a fuel mixture of gasoline and alcohol, preferably a fuel mixture of gasoline and ethanol.

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