Ever more stringent regulations regarding permissible pollutant emissions by motor vehicles fitted with internal combustion engines make it necessary to keep the pollutant emissions as low as possible during operation of the internal combustion engine. One of the ways in which this can be done is by reducing the emissions which occur during the combustion of the air/fuel mixture in the relevant cylinder of the internal combustion engine. Another is to use exhaust gas post processing systems in internal combustion engines which convert the emissions which are generated during the combustion process of the air/fuel mixture in the relevant cylinder into harmless substances. Catalytic converters are used for this purpose which convert carbon monoxide, hydrocarbons and nitrous oxide into harmless substances.
Both the explicit influencing of the generation of the pollutant emissions during the combustion and also the conversion of the pollutant components with a high level of efficiency by an exhaust gas catalytic converter require a very precisely set air/fuel ratio in the respective cylinder.
A linear closed-loop Lambda control with a linear Lambda probe which is arranged upstream from an exhaust gas catalytic converter and a binary Lambda probe which is arranged downstream of the exhaust gas catalytic converter is known from the German textbook, “Handbuch Verbrennungsmotor (Internal Combustion Engine Handbook)”, published by Richard von Basshuysen, Fred Schäfer, 2nd Edition, Vieweg & Sohn Verlagsgesellschaft mbH, June 2002, Pages 559-561. A Lambda setpoint value is filtered by means of a filter which takes account of gas delay times and the sensor behavior. The Lambda setpoint value filtered in this way is the closed-loop control variable of a PII2D Lambda controller, for which the manipulated variable is an injection volume correction.
Furthermore a binary Lambda controller is also known from the same textbook on the same page, with a binary Lambda probe which is arranged upstream of the exhaust gas catalytic converter. The binary Lambda controller comprises a PI closed-loop controller, with the P- and I proportions being held in engine maps covering engine speed and load. With the binary Lambda controller the excitation of the catalytic converter CC, also known as the Lambda fluctuation, is implicitly produced by the two-level control. The amplitude of the Lambda fluctuation is set to around 3%.
DE 103 07 004 B3 discloses extracting, as function of the temperature of the internal combustion engine, an adaptation value for the required fuel amount of a characteristic curve and checking during Lambda control whether predetermined adaptation conditions exist. If they do, an adaptation value is determined from the controller parameters of the Lambda control and the characteristic curve is adapted as a function of the newly determined adaptation value and the measured temperature of the internal combustion engine.
The underlying object of the invention is to create a method and a device for operating an internal combustion engine which are respectively simple and also precise.
The object is achieved by the features of the independent claims. Advantageous embodiments of the invention are identified in the subclaims.
One embodiment of the invention is characterized by a method or a corresponding device for operating an internal combustion engine with at least one a cylinder with a combustion chamber, an injection valve, which is designed for metering of fuel. A Lambda controller is provided. A Lambda adaptation value assigned to a respective temperature range is adapted as a function of at least one corrective signal of the Lambda controller with regard to a control parameter of Lambda controller and this is done if a respective predetermined condition is fulfilled which demands that a quasi-stationary operating state obtains and the respective temperature range is adopted. The respective Lambda adaptation value is assigned to a respective reference temperature in the respective temperature range. A fuel mass to be metered is determined as a function of at least one operating variable of the internal combustion engine. The fuel mass to be metered is corrected as a function of the respective Lambda adaptation value assigned to the current temperature. If a predetermined test condition is fulfilled a check is made as to which of the Lambda adaptation values was adapted as a function of the at least one corrective signal proportion since the test condition was last fulfilled. In addition a Lambda adaptation value not adapted as a function of the at least one respective corrective value which, as regards its respective assigned temperature range, is adjacent to a respective Lambda adaptation value adapted by the at least one corrective signal proportion, is checked as to whether it lies in a range of valid values, which diverges in a predetermined manner as regards the reference temperature of the respective adjacent adapted Lambda adaptation value starting from the respective adapted Lambda adaptation value.
If it lies outside the predetermined diverging range of valid values, the non-adapted Lambda adaptation value will be adapted so that it lies at approximately the closest boundary of the range of valid values in relation of its value before adaptation.
In this way it can be easily ensured that Lambda adaptation values which, between two consecutive times at which the predetermined checking condition is fulfilled, could not be adapted as a function of the corrective signal of the Lambda controller, can then still be adapted.
In this context use is made of the knowledge that a certain correlation exits between the Lambda adaptation values and thus an adaptation of a respective Lambda adaptation value as a function of the at least one corrective signal proportion of the Lambda controller can be used in respect of the one control parameter in order to also adapt the respective adjacent Lambda adaptation value if this not has not been adapted previously as a function of the corrective signal proportion.
This enables a simple contribution to be made to supplying the Lambda adaptation values with the most precise data possible and thus setting the air/fuel-ratio in the respective combustion chamber precisely.
The predetermined checking condition can for example be fulfilled as a function of time.
In accordance with an advantageous embodiment the respective range of validity values is predetermined in a V shape starting from the respective adapted Lambda adaptation value. In this way the respective range of validity values can be computed especially easily and the respective parameters for its definition need relatively little storage space.
In accordance with a further advantageous embodiment a respective non-adapted adaptation value, which has two neighboring values as regards temperature, will be checked as regards two respective Lambda adaptation values depending on the at least one corrective signal proportion as to whether it lies in at least in one of the ranges of valid values, which diverge in a predetermined manner as regards the temperature starting from the respective adapted Lambda adaptation value. If it lies outside one of the two predetermined diverging ranges of valid values in each case, the respective non-adapted Lambda adaptation value is adapted so that it lies approximately at the closest boundary as regards it value before the adaptation of the two respective ranges of valid values. In this way an especially simple and, in the respect of a precise metering of the fuel mass, effective adaptation is possible.
In accordance with a further advantageous embodiment a Lambda adaptation value not adapted as a function of the at least corrective signal proportion, which as regards the temperature range assigned to it, is only indirectly adjacent to a respective Lambda adaptation value adapted as a function of the at least one corrective signal proportion, is checked as to whether it lies in a range of valid values which diverges in a predetermined manner as regards the respective reference temperature starting from the respective adjacent adaptation value. If it lies outside the predetermined diverging range of valid values, the non-adapted Lambda adaptation value will be adapted, so that it is displaced by a proportion defined by a trust factor of a distance to the closest boundary of the range of valid values in the direction of the closest boundary of the range of valid values as regards its value before adaptation. In this way a precise adaptation of only indirectly adjacent adaptation values to a respective Lambda adaptation value adapted as a function of the at least one corrective signal is possible. The trust factor, which can be determined empirically for example, also enables any possible uncertainty that may arise to be taken into account.
In this context it is advantageous, as the indirection of the adjacency to a respective Lambda adaptation value adapted as a function of the at least one corrective signal proportion increases, for the trust factor to be predetermined as a reduced value. In this way use is made of the knowledge that as the indirection increases, an uncertainty as regards the correlation in respect of the range of valid values increases.
In accordance with a further advantageous embodiment, for an immediately adjacent adapted Lambda adaptation value on the one side and an indirectly adjacent further adapted Lambda adaptation value on the other side, the range of valid values of the directly adjacent Lambda adaptation value is considered as definitive and thus the adaptation is undertaken on this basis and this is done especially not taking into account the only indirectly adjacent further adapted Lambda adaptation value and the range of valid values assigned thereto.
In accordance with a further advantageous embodiment the trust factor depends on the distribution of the Lambda adaptation values, which were adapted as a function of the at least one corrective signal proportion. In this way the knowledge can be used that a small distribution of the Lambda adaptation values adapted as a function of the corrective signal is a symptom of the strong dependency of the Lambda adaptation values on the fuel quality and thus for example the trust factor is embodied so that it reduces relatively little, i.e. especially reduces less than with a greater distribution, and does so as the indirection increases. In this way the air/fuel mixture can be set even more precisely.
Elements with identical construction or which function in the same way are identified by the same reference symbols in all figures.