Method for operating an internal combustion engine and corresponding internal combustion engine

Abstract

The invention relates to a method for operating an internal combustion engine comprising at least one turbocharger, at least one catalytic converter and a variable valve train, a valve overlap parameter being determined in at least one operating mode of the internal combustion engine and being used to set the valve train. According to the invention, the valve overlap parameter is adapted on the basis of at least one parameter for the condition of the catalytic converter and/or at least one parameter for the condition of the turbocharger, prior to being used to set the valve train. The invention also relates to an internal combustion engine.

Claims

1. A method for operating an internal combustion engine comprising an exhaust turbocharger, a catalytic converter and a variable valve train, the method comprising the steps of: determining a valve overlap parameter in an operating mode of the internal combustion engine; adjusting the valve overlap parameter on the basis of one selected from the group of catalyst state parameters consisting of an oxygen fill level of the catalyst and a total operation time of the catalyst; and adjusting the valve overlap parameter to the valve train.

2. The method according to claim 1, wherein a scavenging mode is used as the operating mode, for which the rotational speed of the internal combustion engine is at most 50%, at most 40%, at most 30%, at most 20% or at most 10% of a maximum rotational speed, and the torque is at least 25%, at least 50%, at least 60%, at least 70%, at least 80% or at least 90% of a maximum torque.

3. The method according to claim 1, wherein the group of catalyst state parameters further consists of a catalyst temperature and a catalyst volume.

4. The method according to claim 1, further adjusting the valve overlap parameter on the basis of an exhaust gas turbocharger rotational speed.

5. The method according to claim 1, further determining the oxygen fill level on the basis of a model based on a lambda value and an exhaust mass flow rate, and reducing the valve overlap during adjustment of the valve overlap parameter when the oxygen fill level exceeds a preset fill level.

6. The method according claim 1, further determining the reduction of the valve overlap from the difference between the oxygen fill level and a preset fill level.

7. The method according to claim 5, further determining the preset fill level from a catalyst temperature, a catalyst volume and a total operating time of the catalyst.

8. The method according to claim 1, wherein when adjusting the valve overlap parameter, reducing the valve overlap parameter when the exhaust gas turbocharger rotational speed is greater than or equal to a preset rotational speed.

9. The method according to claim 7, further comprising the steps of: determining a fuel injection amount from an amount of air introduced into a cylinder of the internal combustion engine; and adjusting the fuel injection amount when the oxygen fill level exceeds the preset fill level and the catalyst temperature exceeds a preset temperature.

10. An internal combustion engine comprising an exhaust turbocharger, a catalytic converter and a variable valve train, configured to: determine a valve overlap parameter in an operating mode of the internal combustion engine; adjust the valve overlap parameter on the basis of one selected from the group of catalyst state parameters consisting of an oxygen fill level of the catalyst and a total operation time of the catalyst; and adjust the valve overlap parameter to the valve train.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The invention is explained in greater detail based on the exemplary embodiments illustrated in the drawings, without limiting the invention. The sole FIG. 1 shows a schematic representation of a method for operating an internal combustion engine.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(2) A method for operating an internal combustion engine is shown as an example in the FIGURE. The internal combustion engine has an exhaust gas turbocharger, a catalyst and a variable valve train. The variable valve train is used to change valve timing of the intake valves and/or exhaust valves, preferably of both, of the internal combustion engine. In particular, a valve overlap can be set by means of the valve train. By this, a period of time is understood during which both the intake valve and the exhaust valve of a cylinder of the internal combustion engine are simultaneously opened. The method is implemented, for example, by means of a control device of the internal combustion engine.

(3) A load or rather a torque of the internal combustion engine is provided along arrow 1 as an input variable and the rotational speed of the internal combustion engine is provided along arrow 2. The load or rather the torque and rotational speed together define the operating point of the internal combustion engine. It is determined whether a normal mode or a scavenging mode is to be performed as part of evaluation 3. In the former, the valve overlap is smaller than in scavenging mode or even equal to zero. Conversely, the valve overlap in the scavenging mode is correspondingly greater than in the normal mode, in particular greater than zero.

(4) If the scavenging mode is to be implemented, the partial method indicated in box 4 is performed. First, a valve overlap parameter (which is output along arrow 6) is determined from a engine characteristic map 5, which has the torque and the rotational speed as input variables. In the normal mode, this valve overlap parameter is set directly on the internal combustion engine or rather the variable valve train. In the scavenging mode, an effective overlap is now calculated in an evaluation 7, from which in turn as part of an evaluation 8, an air mass flushed through by a cylinder of the internal combustion engine is determined. This air mass is output along arrow 9.

(5) As part of an evaluation 10, a flush rate is determined from the air mass, which is used as part of an evaluation 11 in a calculation of a lambda set point. In addition, the air mass determined as part of the evaluation 8 forms an input parameter of a subtractor 12 whose output variable is output along arrow 13 and is then used to determine a fuel injection quantity as part of an evaluation 14. Another input variable of the subtractor 12 represents an amount of air introduced into the cylinder, which is supplied to the subtractor 12 along arrow 15. In the subtractor 12, the purged air mass is subtracted from the calculated air mass 15 and the result supplied to the evaluation 14.

(6) The inventive method is characterized in that the valve overlap parameter is adjusted before the setting on the valve train, based on at least one catalyst state parameter and/or at least one exhaust gas turbocharger state parameter. For this purpose, an oxygen fill level of the catalyst is first determined as part of an evaluation 16, and provided along arrow 17. The oxygen fill level thereby represents a catalyst state parameter. Further catalyst state parameters of an evaluation 18 are supplied along the arrows 19, 20 and 21, namely, in this order: a catalyst temperature, catalyst volume, and a total operating time of the catalyst. A preset fill level is determined from the input variables supplied along the arrows 17, 19, 20 and 21 as part of the evaluation 18 and compared with the oxygen fill level. For example, a difference between the oxygen fill level and the preset fill level is thereby determined. This difference can be subsequently used in an evaluation 22 for determining a first correction value. This first correction value is supplied along arrow 23 to an adder.

(7) As part of an evaluation 25, the exhaust gas turbocharger rotational speed, which is used as an exhaust gas turbocharger state parameter, can be compared with a preset rotational speed. If the exhaust gas turbocharger rotational speed is greater than or equal to the preset rotational speed, a second correction value is determined as part of evaluation 26 and also supplied to the adder 24 along arrow 27. In particular, the second correction value is selected such that the valve overlap is reduced when the exhaust gas turbocharger rotational speed is greater than or equal to the preset rotational speed. The two correction values are added by the adder 24 and the result supplied to a subtractor 29 along arrow 28, which has the valve overlap parameter as a further input variable along arrow 6. The result of the adder 24 is now used to adjust the valve overlap parameter, in particular, it is subtracted from the valve overlap parameters. The result is then supplied to the evaluation 7 and/or set on the variable valve train.

(8) Furthermore, it can be provided that the catalyst temperature is supplied to an evaluation 31 along arrow 30, which in addition, has the oxygen fill level of the catalyst as an input variable. If it is detected that the oxygen fill level exceeds the preset fill level and/or the catalyst temperature exceeds a preset temperature, the previously determined fuel injection quantity can be adjusted as part of the evaluation 14 on this basis. With the above-described method for operating the internal combustion engine, it is possible to provide a very high torque by means of the internal combustion engine even at low rotational speeds, wherein exhaust emission limits can be met readily at the same time.