WO2009036890A2

WO2009036890A2 - Method and device for determining the deviation of a lambda value from a total lambda value of at least one cylinder of an internal combustion engine

Info

Publication number: WO2009036890A2
Application number: PCT/EP2008/007225
Authority: WO
Inventors: Peter Hohner; Michael Oechsle; Martin-Claudio Schuler
Original assignee: Daimler Ag
Priority date: 2007-09-13
Filing date: 2008-09-04
Publication date: 2009-03-26
Also published as: DE102007043734A1

Description

Method and device for determining a deviation of a lambda value of at least one cylinder of an internal combustion engine from a total lambda value

The invention relates to a method for determining a deviation of a lambda value of at least one cylinder of an internal combustion engine, in particular a gasoline and / or diesel engine of a motor vehicle, from a total lambda value and a device for determining a deviation of a lambda value at least one cylinder of an internal combustion engine in the preamble of claim 7 specified type.

Such a method and such a device are, for example, already known from DE 101 15 902 C1 as known. In this case, a total lambda value and an exhaust gas value are continuously determined in an exhaust gas tract of a multi-cylinder internal combustion engine designed as a gasoline engine by means of a sensor device designed as a lambda probe. The exhaust gas value then shows a local minimum, if not only the total lambda value but also the individual lambda values of all cylinders amount to 1, 0. By controlling a cylinder-individual fuel supply followed by a pair of trim all cylinders of the internal combustion engine, in each of which increases the lambda value of a cylinder and the lambda dada value of the other cylinder is lowered, the average total lambda value of both cylinders is kept constant at 1, 0 , The trimming is carried out until no deviations of the individual lambda values of all cylinders from the total lambda value of the internal combustion engine are present and the exhaust gas value has reached a local minimum. The differences between the output lambda values and the adjusted lambda values of each cylinder thus correspond in each case to the deviation originally present. Object of the present invention is to provide a method and an apparatus of the type mentioned, which allow a more flexible and faster determination of a deviation of a lambda value of at least one cylinder of an internal combustion engine from a total lambda value.

The object is achieved by a method for determining a deviation of a lambda value of at least one cylinder of an internal combustion engine from a total lambda value according to claim 1 and by a device for determining a deviation of a lambda value of at least one cylinder of an internal combustion engine from a total lambda value with the characteristics of Patent claim 7 solved. Advantageous developments of the invention are specified in the dependent claims, wherein advantageous developments of the method - where applicable - are to be regarded as advantageous developments of the device.

A method, which allows a more flexible and faster determination of a deviation of a lambda value of at least one cylinder of an internal combustion engine from a total lambda value, comprises according to the invention the steps a) operating the at least two cylinders with a first total lambda value, b) determining at least one first smooth running value c) operating the at least two cylinders with a second total lambda value, d) determining at least one second running rest value of the at least one cylinder by means of the running rest determining device, and e) determining the deviation of the lambda value from the total lambda value based on a comparison of the first and the second running noise value. Since the method according to the invention can be carried out without the aid of additional sensor devices and the determination of the deviation of the lambda value can be carried out in a conventional engine control unit, it can be carried out in a particularly flexible manner and used both in internal combustion engines designed as an Otto engine and as a diesel engine. It is irrelevant whether the internal combustion engine is provided with a turbocharger, which previously made impossible due to the homogenization of the total lambda value determination of the deviation of lambda values of individual cylinders, or at least severely hampered. In contrast to the prior art, the method can also be performed much faster especially in internal combustion engines with six or more cylinders, since no pairwise permutations must be performed. Determining the deviation of the lambda value of the at least one cylinder further allows for targeted control of its fuel feed to obtain the desired blend composition. As a result, it is possible to ensure an improvement in the exhaust gas quality and reliable compliance with legal exhaust gas emission limits. Furthermore, the smoothness of the internal combustion engine and thus the comfort of the associated motor vehicle can be significantly improved. Due to the adjustable difference between the first and the second total lambda value of the internal combustion engine, it is also possible to exclude undesirable effects of the determination due to retarded combustion, compression losses, uneven residual gas distribution and the like, whereby a particularly reliable and accurate determination of the deviation of the lambda value is ensured.

Another aspect of the invention relates to a device for determining a deviation of a lambda value of at least one cylinder of an internal combustion engine, in particular a gasoline and / or diesel engine of a motor vehicle, from a total lambda value, wherein according to the invention it is provided that these are used to carry out a method according to the previous embodiments is designed. In this way, a more flexible and faster determination of the deviation of the lambda value from the total lambda value is made possible. Further advantages can be found in the previous descriptions.

Further advantages, features and details of the invention will become apparent from the following description of an embodiment and with reference to the drawings, in which the same or functionally identical elements are provided with identical reference numerals.

Showing:

Fig. 1 is a schematic representation of a designed as a gasoline engine

Internal combustion engine with eight cylinders;

Fig. 2 are schematic representations of a relationship between a

Torque of a cylinder of the internal combustion engine shown in Figure 1 as a function of its lambda value when operating the internal combustion engine with a first and a second total lambda value. Fig. 3 is a schematic representation of temporal running rest of the eight

Cylinder of the internal combustion engine shown in Figure 1 as a function of the total lambda value.

Fig. 4 is a schematic representation of temporal running rest of the fifth

Cylinder of the internal combustion engine shown in Figure 1, wherein the mixture composition is corrected in dependence of the deviation of its lambda value from the total lambda value. and

5 shows an algorithm for determining and correcting the lambda values of

Cylinder of the engine shown in Fig. 1.

Fig. 1 shows a schematic diagram of a designed as a V8 gasoline engine 10 for a motor vehicle not shown with eight cylinders 12a-h. Each cylinder 12a-h has a cylinder-specific fuel supply 13, by means of which the respective mixture composition and thus the lambda value λ of each individual cylinder can be controlled. For reasons of clarity, only two fuel supply lines 13a, 13b for each cylinder bank 14a, 14b are depicted, to which the eight cylinders 12a-h are divided in the present exemplary embodiment. In this case, the cylinders 12a-d are assigned a first exhaust gas tract 16a and the cylinders 12e-h a second exhaust gas tract 16b. Each exhaust gas tract 16a, 16b comprises a sensor device 18a, 18b, by means of which the total lambda values Λa of the cylinders 12a-d or the total lambda values Λb of the cylinders 12e-h can be determined. The sensor devices 18a, 18b are coupled to the fuel supply lines 13a, 13b for adjusting the respective mixture compositions. Each cylinder bank 14a, 14b of the internal combustion engine 10 is also assigned a fan unit 20a, 20b in the direction of travel of the motor vehicle. Not shown is a running smoothness determining device of the internal combustion engine 10, which serves to determine running smoothness values of the cylinders 12a-h. Suitable smoothness determining devices are already known from the prior art and include, for example, a sensor wheel coupled to a crankshaft of the internal combustion engine with associated crankshaft sensor, so that a crankshaft angular velocity can be detected and cylinder-specific running smoothness values can be derived. The implementation of the method explained in more detail below can be carried out without problems in conventional engine control units. It should be emphasized that the process also in gasoline engines with a different number of cylinders or design or trained in diesel engines 10 can be performed.

2 shows schematic representations of a relationship between a moment M (λ) of the first four cylinders 12a-d of the internal combustion engine 10 shown in FIG. 1 as a function of their lambda values λ during operation of the internal combustion engine 10 with a first total lambda value Λ1 and one second total lambda value Λ2. In this case, as is apparent from FIG. 1, the first cylinder 12a runs too lean and has a lambda value λ = 1, 3. In order to be able to achieve an overall lambda value Λa = 1.0 of the cylinders 12a-d in the exhaust tract 16a, the remaining cylinders 12b-d of the cylinder bank 14a must be operated with a correspondingly richer mixture composition and therefore have lambda values of λ = 0.9 , Conversely, it can be seen in conjunction with FIG. 1 that the seventh cylinder 12g runs too fat on the cylinder bank 14b and has a lambda value λ = 0.85. Correspondingly, the further cylinders 12e, 12f, 12h must be emaciated and operated with lambda values λ = 1.05 in order to achieve an overall lambda value Λb = 1.0 in the exhaust gas tract 16b. Although both total lambda values Λa, Λb formally correspond to a stoichiometric mixture composition with an overall lambda value Λ = 1.0, the deviations of the lambda values λ of the cylinders 12a-h lead to a deteriorated exhaust quality, an impairment of the smooth running of the internal combustion engine 10 and to a loss of moment M (λ) and driving comfort. The following explanations are explained with reference to the four cylinders 12a-d of the cylinder bank 14a, but apply correspondingly to the cylinders 12e-h of the cylinder bank 14b. By enriching the cylinders 12a-d in accordance with arrow Il, the internal combustion engine 10 is operated with respect to its exhaust gas tract 16a with a second total lambda value Λ2 = 0.8, whereby the moments M (λ) of the cylinders 12a-d in accordance with the arrows IIa or Move IIb along the parabola shown. Cylinder 12a now has a lambda value λ = 0.92 and a maximum torque output. The remaining cylinders 12b-d continue to grease and additionally have reduced moments M (λ). Conversely, an exhaustion of the cylinders 12a-d - for example, when operating the internal combustion engine 10 with a second total lambda value Λ2 = 1, 2 - would lead to an improved torque output of the cylinders 12b-d and a further deteriorated torque output of the cylinder 12a. Thus, what is essential is merely a change in the total lambda value Λ, so that the second overall lambda value Λ2 can optionally be selected to be higher or lower than the first overall lambda value Λ1. FIG. 3 shows a schematic illustration of running smoothness values La-h of the eight cylinders 12a-e of the internal combustion engine 10 shown in FIG. 1 as a function of the time t and of the total lambda value Λ. In this case, the internal combustion engine 10 is first operated with a first total lambda value Λ1 = 1.0, and the running rest values La-h are determined. In the present example, the running noise values La-h are regularly determined and smoothed. Alternatively, only a single running rest value L can be determined for each total lambda value Λ or by averaging. Subsequently, the internal combustion engine 10 is operated by changing the total lambda value Λ with the second overall lambda value Λ2 = 0.8, as a result of which the lambda values λ of the cylinders 12a-h also change. By comparing the smoothness values La-h determined at the first and at the second total lambda value Λ1 or Λ2, the deviations Δ of the lambda values λ of each cylinder 12a-h are then determined. In this case, for example, the running rest values Ld of the cylinder 12d decrease, from which it can be concluded that this is running too lean and its lambda value λ accordingly has a positive deviation Δd from the total lambda value Λ. Conversely, the running rest values Le of the cylinder 12e increase, from which it can be concluded that this is running too rich and its lambda value λ accordingly has a positive deviation Δe from the total lambda value Λ. When changing the overall lambda value Λ back to the first total lambda value Λ1 and thus leaning out of the internal combustion engine 10, correspondingly reversed courses of the steady state values La-h and correspondingly reversed deviations Δ of the individual lambda values λ result, so that the deviations Δ also occur Abmagern the internal combustion engine 10 can be determined.

Fig. 4 shows a schematic representation of temporal rest rest values Le of the fifth cylinder 12e of the internal combustion engine 10 shown in Fig. 1. This results first when changing the total lambda value Λ of the first total lambda value Λ1 to the second total lambda value Λ2 Increase of the running rest value Le and thus a lower torque output of the cylinder 12e running too rich. The deviation Δe of its lambda value λ from the total lambda value Λ is determined in the previously described manner. At time t1, the mixture composition of the cylinder 12e is then corrected as a function of the determined deviation Δe, and the cylinder 12e is supplied with an amount of fuel reduced by 20%. A renewed change of the total lambda value Λ at the time t2 leads - within technical limits - to no change in the running rest values Le, which is why it can be assumed that the cylinder 12e has no mixture deviation from the remaining cylinders 12 of the internal combustion engine 10. This is confirmed by changing the total lambda value Λ again at time t3. The method described can be advantageous for each cylinder 12 to ensure a mixture equality of all cylinders 12. This mixture equalization is thus achieved when the smoothness L of each cylinder does not change when changing the total lambda value Λ. Further advantages result when the method is carried out during a clearing process 22 (see FIG. 5) of a catalytic converter (not shown) during acceleration of the internal combustion engine 10 from the overrun operation. Since in this case the internal combustion engine 10 must anyway be operated for a certain time with an enriched overall lambda value, in order to reduce the amount of oxygen stored in the catalytic converter during the overrun operation, the method can accordingly be carried out in an exhaust-neutral manner. An improvement in the measurement accuracy is achieved in that the method is carried out during an at least approximately stationary operation of the internal combustion engine 10. In this case, it can also be provided that the method is carried out during each clearing process 22 and, in the case of an error suspicion, is specifically carried out again during the next at least approximately stationary operation of the internal combustion engine 10.

FIG. 5 shows an algorithm for determining and correcting the lambda values λ of the cylinders 12 of the internal combustion engine 10 shown in FIG. 1 according to one exemplary embodiment. After starting the clearing process 22, a change 24 of the total lambda value Λ of the internal combustion engine 10 and a determination of the running rest values L are carried out in the manner described above. Subsequently, in step 26, the deviation Δ of its lambda value λ from the total lambda value Λ is determined for each cylinder on the basis of the changes in its running rest values L. If the deviation Δ> 0, the cylinder 12 is too rich and has to be emaciated accordingly in step 28. Conversely, if the deviation Δ <0, the cylinder 12 is too lean and must be greased in step 30 accordingly. Steps 24 to 30 are carried out until the deviation Δ of all cylinders - within certain limits - is zero and all cylinders 12 are therefore to be regarded as equivalent in terms of their combustion air ratio in step 32. From the factors required for enriching or draining the individual cylinders 12, a check is made in the following step 34 as to whether a predetermined limit value has been violated and as a result possibly impermissibly high exhaust emission values are present. If this is the case, a corresponding warning signal is generated in step 36 and, for example, an engine control lamp is activated. This ensures compliance with strict emission regulations.

Claims

claims

1. A method for determining a deviation (.DELTA.) Of a lambda value (λ) of at least one cylinder (12) of an internal combustion engine (10), in particular an Otto and / or diesel engine of a motor vehicle, from a total lambda value (Λ), wherein the internal combustion engine (10) at least two cylinders (12) with a cylinder-specific fuel supply (13) and a sensor device (18) which is arranged in an at least two cylinders (12) associated exhaust tract (16) and by means of which the total lambda value (Λ) the at least two cylinders (12) are determined, comprising the following steps: a) operating the at least two cylinders (12) with a first total lambda value (Λ1); b) determining at least one first running rest value (L) of the at least one cylinder (12) by means of a running smoothness determining device of the internal combustion engine (10); c) operating the at least two cylinders (12) with a second total lambda value (Λ2); d) determining at least one second running rest value (L) of the at least one cylinder (12) by means of the running smoothness determining device; and e) determining the deviation (Δ) of the lambda value (λ) from the total lambda value (Λ) on the basis of a comparison of the first and the second running rest value (L).

2. The method according to claim 1, characterized in that in a further step f) a mixture composition of the at least one cylinder (12) on the basis of the deviation (Δ) of the lambda value (λ) is corrected.

3. The method according to claim 2, characterized in that the steps a) to f) for the at least two and preferably for all cylinders (12) of the internal combustion engine (10) are performed.

4. The method according to any one of claims 1 to 3, characterized in that at least steps a) to e) and optionally f) during a clearing process of a catalyst and / or during an at least approximately stationary operation of the internal combustion engine (10) are performed.

5. The method according to any one of claims 1 to 4, characterized in that in a further step g) is checked whether the at least one cylinder (12) is operated within predetermined limits.

6. The method according to claim 5, characterized in that a warning signal is generated when in step g) a violation of the limits is detected.

7. Device for determining a deviation (.DELTA.) Of a lambda value (λ) of at least one cylinder (12) of an internal combustion engine (10), in particular of a gasoline engine and / or diesel engine of a motor vehicle, from an overall lambda value (Λ), wherein the internal combustion engine (10) at least two cylinders (12) with cylinder-individual fuel supply (13), a running smoothness determining device for determining a running rest value (L) of the at least two cylinders (12) and a sensor device (18) which in one of the at least two cylinders (12) assigned exhaust tract (16) is arranged and by means of which the total lambda value (Λ) of the at least two cylinders (12) can be determined, characterized in that it is designed to carry out a method according to one of claims 1 to 6.