Method for operating an internal combustion engine

1. A method for operating an internal combustion engine with venting via a breather of a crankcase into an intake tract, comprising the following steps:

measuring one or more operating parameters of the internal combustion engine;

calculating a mass blow-by flow of fuel from the crankcase into the intake tract as a function of the one or more operating parameters measured;

defining a permissible range of a fuel-air ratio between the fuel supplied to the internal combustion engine and fresh air supplied to the internal combustion engine as a function of the calculated mass blow-by flow of fuel;

determining an actual fuel-air ratio in the internal combustion engine;

comparing (a) the determined actual fuel-air ratio with (b) the permissible range of a fuel-air ratio defined as a function of the calculated mass blow-by flow of fuel; and

based at least on the comparison, controlling or ascertaining operability or malfunction of the internal combustion engine.

2. The method according to claim 1 , further comprising the following steps:

checking the plausibility of the calculated mass blow-by flow of fuel; and

ascertaining the operability of the internal combustion engine as a function of the plausibility of the calculated mass blow-by flow of fuel.

3. The method according to claim 2 , wherein the plausibility of the calculated mass blow-by flow of fuel is checked on the basis of the change over time of the calculated mass blow-by flow of fuel.

4. The method according to claim 1 , further comprising the following step:

setting a precontrol parameter of the internal combustion engine as a function of the calculated mass blow-by flow of fuel.

5. The method according to claim 1 , further comprising the following steps:

at starting, increasing a model parameter representing the mass of fuel dissolved in the lubricant of the internal combustion engine; and

reducing the model parameter during operation of the internal combustion engine.

6. The method according to claim 5 , wherein the model parameter is increased at starting by an amount which depends on the temperature of the internal combustion engine measured at least one time instant.

7. The method according to claim 5 , wherein the model parameter is increased at starting by an amount which depends on the change over time of a temperature of the internal combustion engine.

8. The method according to claim 5 , wherein the model parameter is increased at starting by an amount which depends on a mass of fuel injected within a predetermined time interval or until a predetermined operating temperature of the internal combustion engine is attained.

9. The method according to claim 1 , further comprising the following steps:

setting a model parameter representing the mass of the fuel dissolved in a lubricant of the internal combustion engine to a predetermined initial value at starting; and

reducing the model parameter during operation of the internal combustion engine.

10. The method according to claim 9 , wherein the predetermined initial value is a function of a temperature of the internal combustion engine at starting.

11. The method according to claim 5 , wherein during operation of the internal combustion engine the model parameter is reduced at a plurality of time instants by an amount dependent on the operating parameters measured at the respective time instant.

12. The method according to claim 5 , wherein during operation of the internal combustion engine the model parameter is reduced at a plurality of time instants by an amount dependent on the mass blow-by flow of fuel that was calculated as a function of the operating parameters measured at the respective time instant.

13. The method according to claim 11 , wherein a distinction is drawn between first time instants at which the internal combustion engine is in a predetermined operating state, and second time instants at which the internal combustion engine is not in the predetermined operating state,

at a first time instant, the reduction amount is determined as a function of the operating parameters measured at the respective first time instant,

at a second time instant, the reduction amount is determined as a function of an operating parameter of the internal combustion engine and of a fuel concentration in the crankcase breather, the fuel concentration being determined as a function of operating parameters measured at the most recent time instant.

14. The method according to claim 1 , further comprising the following steps:

determining an end of a discharge of fuel from a lubricant of the internal combustion engine; and

ascertaining operability or malfunction of the internal combustion engine after the end of discharge.

15. The method according to claim 1 , further comprising the following steps:

determining an end of discharge of fuel from a lubricant of the internal combustion engine;

after the end of discharge determined, reducing a permissible range of a ratio of fuel supplied to the internal combustion engine to fresh air supplied to the internal combustion engine, and

wherein the operability of the internal combustion engine is monitored by comparing the ratio of the fuel supplied to the internal combustion engine to the fresh air supplied to the internal combustion engine with the permissible range.

16. A computer readable program product stored in non-transitory storage media and operable, when executed, to:

calculate a mass blow-by flow of fuel from the crankcase into the intake tract as a function of one or more measured operating parameters of the internal combustion engine;

define a permissible range of a fuel-air ratio between the fuel supplied to the internal combustion engine and fresh air supplied to the internal combustion engine as a function of the calculated mass blow-by flow of fuel;

compare (a) an actual fuel-air ratio in the internal combustion engine with (b) the permissible range of a fuel-air ratio defined as a function of the calculated mass blow-by flow of fuel; and

control, or monitor operability of, the internal combustion engine based at least on the results of the comparison.

17. A device for controlling and/or monitoring the operability of an internal combustion engine, the device configured to execute a program product stored in non-transitory storage media to:

calculate a mass blow-by flow of fuel from the crankcase into the intake tract as a function of one or more measured operating parameters of the internal combustion engine;

define a permissible range of a fuel-air ratio between the fuel supplied to the internal combustion engine and fresh air supplied to the internal combustion engine as a function of the calculated mass blow-by flow of fuel;

compare (a) an actual fuel-air ratio in the internal combustion engine with (b) the permissible range of a fuel-air ratio defined as a function of the calculated mass blow-by flow of fuel; and

control, or monitor operability of, the internal combustion engine based at least on the results of the comparison.