Method and control device for operating an internal combustion engine

1. A method for operating an internal combustion engine having multiple cylinders, wherein the internal combustion engine comprises at least one fuel injector for each cylinder, comprising:

activating for opening and closing each fuel injector via a respective solenoid valve of each fuel injector;

detecting by measurement over time structure-borne sound waves emitted by each fuel injector commencing with the activation of each respective fuel injector for opening;

evaluating the detected structure-borne sound waves such that an operating mode of the respective fuel injector is deduced based at least in part on:

an amount of at least one maximum of a structure-borne sound wave signal,

and/or

a number of maximums of the structure-borne sound wave signal and/or

a presence of multiple maximums dependent on a time sequence and/or

an amount a respective one maximum,

wherein the operating mode is one of a diesel operating mode and a gas operating mode,

wherein the activating for opening and closing each fuel injector is based at least in part on the operating mode.

2. The method according to claim 1 , wherein a first operating state of the respective fuel injector is deduced when a first maximum occurs in the structure-borne sound wave signal detected by measurement, whose amount is greater than a first limit value (G 1 ), within a defined first period (Δt 1 ) following commencement of the activation of the respective fuel injector for opening.

3. The method according to claim 2 , wherein the first operating state of the respective fuel injector is an operating state of a first quantity injection of fuel into the respective cylinder.

4. The method according to claim 2 , wherein a second operating state or third operating state of the respective fuel injector is deduced when, within the defined first period (Δt 1 ) following the commencement of the activation of the respective fuel injector for opening, the first maximum occurs in the structure-borne sound wave signal detected by measurement whose amount is smaller than the first limit value (G 1 ) but greater than a second limit value (G 2 ).

5. The method according to claim 4 , wherein

the second operating state is deduced when the first maximum occurs in the structure-borne sound wave signal within the defined first period (Δt 1 ) whose amount is smaller than the first limit value (G 1 ) but greater than the second limit value (G 2 ), no further maximum occurs whose amount is greater than the second limit value (G 2 );

the second operating state is deduced when the first maximum occurs in the structure-borne sound wave signal within the defined first period (Δt 1 ) whose amount is smaller than the first limit value (G 1 ) but greater than the second limit value (G 2 ), and following within the defined first period (Δt 1 ) or within a defined second period (Δt 2 ) following the occurrence of the first maximum, a second maximum occurs whose amount is greater than the second limit value (G 2 ); and

the third operating state is deduced when the first maximum occurs in the structure-borne sound wave signal within the defined first period (Δt 1 ) whose amount is smaller than the first limit value (G 1 ) but greater than the second limit value (G 2 ) and when following this a second maximum occurs however not within the defined first period (Δt 1 ) or not within the defined second period (Δt 2 ) but within a longer period (Δt 3 ) after the occurrence of the first maximum.

6. The method according to claim 4 , wherein the third operating state of the respective fuel injector is an operating state of a full stroke of a nozzle needle of the respective fuel injector.

7. The method according to claim 4 , wherein the third operating state of the respective fuel injector is an operating state of a third quantity injection of fuel into the respective cylinder.

8. The method according to claim 4 , wherein the second operating state of the respective fuel injector is an operating state of a ballistic opening state of a nozzle needle of the respective fuel injector.

9. The method according to claim 7 wherein the second operating state of the respective fuel injector is an operating state of a second quantity injection of fuel into the respective cylinder which is greater than a first quantity injection and smaller than the third quantity injection.

10. A control device for operating an internal combustion engine having multiple cylinders, wherein the internal combustion engine comprises at least one fuel injector for each cylinder, the control device configured to:

activate for opening and closing each fuel injector via a respective solenoid valve of each fuel injector;

detect by measurement over time structure-borne sound waves emitted by each fuel injector commencing with the activation of each respective fuel injector for opening;

evaluate the detected structure-borne sound waves such that an operating mode of the respective fuel injector is deduced based at least in part on:

an amount of at least one maximum of a structure-borne sound wave signal, and/or

a number of maximums of the structure-borne sound wave signal and/or

a presence of multiple maximums dependent on a time sequence and/or

an amount a respective one maximum,

wherein the operating mode is one of a diesel operating mode and a gas operating mode, and

wherein the activating for opening and closing each fuel injector is based at least in part on the operating mode.