Method and device for diagnosing an internal combustion engine of a powertrain

1. A method for diagnosing an internal combustion engine of a powertrain, the powertrain includes the internal combustion engine and a transmission unit, the diagnosis is carried out using a running irregularity signal, the method comprising:

ascertaining a diagnostic value of the internal combustion engine during operation using the running irregularity signal of the internal combustion engine, wherein the powertrain is operated using a diagnostic gear of the transmission unit;

detecting the diagnostic gear which is engaged in the transmission unit while ascertaining the diagnostic value; and

comparing the ascertained diagnostic value with a predefined diagnostic threshold value and comparing the diagnostic gear of the transmission unit with at least one predefined gear of the transmission unit;

identifying that the diagnosis of the internal combustion engine is reliable and there is a fault of the internal combustion engine if the ascertained diagnostic value exceeds the predefined diagnostic threshold value and at the same time the diagnostic gear of the transmission unit differs from all of the predefined gears of the transmission unit, or

identifying that the diagnosis of the internal combustion engine is unreliable if the ascertained diagnostic value exceeds the predefined diagnostic threshold value and at the same time the diagnostic gear of the transmission unit corresponds to one of the predefined gears of the transmission unit.

2. The method of claim 1 , wherein the ascertainment of the diagnostic value is repeated if a gear change has been performed by the transmission unit, and wherein it is identified that the diagnosis of the internal combustion engine is reliable and there is the fault if the diagnostic value ascertained during the repetition exceeds the predefined diagnostic threshold value and at the same time the diagnostic gear of the transmission unit differs from all of the predefined gears of the transmission unit.

3. The method of claim 1 , wherein a gear change request is actively sent to the transmission unit if the ascertained diagnostic value exceeds the predefined diagnostic threshold value and at the same time the diagnostic gear of the transmission unit corresponds to one of the predefined gears of the transmission unit.

4. The method of claim 3 , wherein the predefined gears are blocked by the transmission unit until the ascertainment of the diagnostic value is completed in a gear different from the predefined gears.

5. The method of claim 4 , wherein the gear change and/or the gear block of the transmission unit are performed in dependence on driver requirements or powertrain requirements.

6. The method of claim 1 , wherein a cylinder-specific diagnostic value is ascertained by a cylinder-specific running irregularity signal for each individual cylinder of the internal combustion engine.

7. The method of claim 6 , wherein, during a predefined first time period, one of the cylinders of the internal combustion engine is made leaner in comparison to other cylinders of the internal combustion engine and the cylinder-specific running irregularity signal detected during this first time period is used to ascertain the cylinder-specific diagnostic value of the corresponding cylinder.

8. The method of claim 1 , wherein an input is entered into a fault memory if it is identified that the diagnosis of the internal combustion engine is reliable and there is the fault, and wherein the input is left out of the fault memory if it is identified that the diagnosis of the internal combustion engine is unreliable.

9. A device for diagnosing an internal combustion engine of a powertrain, wherein the powertrain has the internal combustion engine and a transmission unit, and the diagnosis is made by a running irregularity signal, the device comprising:

a control unit designed to carry out a method comprising:

ascertaining a diagnostic value of the internal combustion engine during operation using the running irregularity signal of the internal combustion engine, wherein the powertrain is operated using a diagnostic gear of the transmission unit;

detecting the diagnostic gear which is engaged in the transmission unit while ascertaining the diagnostic value; and

comparing the ascertained diagnostic value with a predefined diagnostic threshold value and comparing the diagnostic gear of the transmission unit with at least one predefined gear of the transmission unit;

identifying that the diagnosis of the internal combustion engine is reliable and there is a fault of the internal combustion engine if the ascertained diagnostic value exceeds the predefined diagnostic threshold value and at the same time the diagnostic gear of the transmission unit differs from all of the predefined gears of the transmission unit, or

identifying that the diagnosis of the internal combustion engine is unreliable if the ascertained diagnostic value exceeds the predefined diagnostic threshold value and at the same time the diagnostic gear of the transmission unit corresponds to one of the predefined gears of the transmission unit.

10. The device of claim 9 , wherein the ascertainment of the diagnostic value is repeated if a gear change has been performed by the transmission unit, and wherein it is identified that the diagnosis of the internal combustion engine is reliable and there is the fault if the diagnostic value ascertained during the repetition exceeds the predefined diagnostic threshold value and at the same time the diagnostic gear of the transmission unit differs from all of the predefined gears of the transmission unit.

11. The device of claim 9 , wherein a gear change request is actively sent to the transmission unit if the ascertained diagnostic value exceeds the predefined diagnostic threshold value and at the same time the diagnostic gear of the transmission unit corresponds to one of the predefined gears of the transmission unit.

12. The device of claim 11 , wherein the predefined gears are blocked by the transmission unit until the ascertainment of the diagnostic value is completed in a gear different from the predefined gears.

13. The device of claim 12 , wherein the gear change and/or the gear block of the transmission unit are performed in dependence on driver requirements or powertrain requirements.

14. The device of claim 9 , wherein a cylinder-specific diagnostic value is ascertained by a cylinder-specific running irregularity signal for each individual cylinder of the internal combustion engine.

15. The device of claim 14 , wherein, during a predefined first time period, one of the cylinders of the internal combustion engine is made leaner in comparison to other cylinders of the internal combustion engine and the cylinder-specific running irregularity signal detected during this first time period is used to ascertain the cylinder-specific diagnostic value of the corresponding cylinder.

16. The device of claim 9 , wherein an input is entered into a fault memory if it is identified that the diagnosis of the internal combustion engine is reliable and there is the fault, and wherein the input is left out of the fault memory if it is identified that the diagnosis of the internal combustion engine is unreliable.