Method for diagnosing the leakage of an injector and associated control device

1. A method for diagnosing the leakage of an injector which serves for injecting fuel into a combustion chamber of at least one cylinder of a combustion engine, the method comprising the steps of:

in an observation time window during which the particular injector of the combustion engine that is to be tested is deactivated, detecting whether a deviation of a speed curve of the combustion engine has occurred relative to a reference speed curve which indicates injector leak-tightness, and in the event that a deviation is detected, determining that there is a leakage of said injector.

2. The method according to claim 1 , wherein in a first observation time window which lies in a period of time between an activation time of a starter unit of the combustion engine for the purpose of rotating its crankshaft and an activation time of an ignition system of the combustion engine, an engine speed of the combustion engine is observed during the latter's starting operation, and in said first observation time window a leakage of the particular injector that is to be tested is diagnosed if a speed increase above a calibration threshold is registered in the first observation time window, said calibration threshold being chosen greater than a target speed of the combustion engine attainable by the starter unit on its own.

3. The method according to claim 1 , wherein in a second observation time window which lies in a period of time between the activation time of the ignition system of the combustion engine and an activation time of an injection control system of the combustion engine, an engine speed of the combustion engine is observed during the latter's starting operation, and a leakage of the particular injector that is to be tested is diagnosed if a speed increase above a calibration threshold is registered in the second observation time window, said calibration threshold being chosen greater than a target speed of the combustion engine attainable by a starter unit on its own.

4. The method according to claim 1 , wherein the diagnosis is stopped as soon as the fuel injection of at least one injector is released.

5. The method according to claim 1 , wherein during a third observation time window which lies in the period of time between a time of a deactivation of all injectors of the combustion engine and a time of the deactivation of the ignition system of the combustion engine, the decrease in an engine speed is observed, and the leakage of the particular injector that is to be tested is diagnosed if during said third observation time window the engine speed exceeds a calibration threshold which is greater than the values of the engine speed if the injector is leak-tight.

6. A control device for diagnosing the leakage of an injector which serves for injecting fuel into the combustion chamber of at least one cylinder of a combustion engine, comprising:

a diagnostic unit operable to detect, in an observation time window during which the particular injector of the combustion engine that is to be tested is deactivated, whether a deviation of a speed curve of the combustion engine has occurred relative to a reference speed curve which indicates injector leak-tightness, and in the event that a deviation is detected, is further operable to determine that there is a leakage of said injector.

7. The device according to claim 6 , wherein the diagnostic unit is further operable to observe, in a first observation time window which lies in a period of time between an activation time of a starter unit of the combustion engine for the purpose of rotating its crankshaft and an activation time of an ignition system of the combustion engine, an engine speed of the combustion engine during the latter's starting operation, and to diagnose in said first observation time window a leakage of the particular injector that is to be tested if a speed increase above a calibration threshold is registered in the first observation time window, wherein said calibration threshold is chosen greater than a target speed of the combustion engine attainable by the starter unit on its own.

8. The device according to claim 6 , wherein the diagnostic unit is further operable to observe, in a second observation time window which lies in a period of time between the activation time of the ignition system of the combustion engine and an activation time of an injection control system of the combustion engine, an engine speed of the combustion engine during the latter's starting operation, and to diagnose a leakage of the particular injector that is to be tested if a speed increase above a calibration threshold is registered in the second observation time window, wherein said calibration threshold is chosen greater than a target speed of the combustion engine attainable by a starter unit on its own.

9. The device according to claim 6 , wherein the diagnostic unit is further operable to stop the diagnosis as soon as the fuel injection of at least one injector is released.

10. The device according to claim 6 , wherein the diagnostic unit is further operable to observe, during a third observation time window which lies in the period of time between a time of a deactivation of all injectors of the combustion engine and a time of the deactivation of the ignition system of the combustion engine, the decrease in an engine speed, and to diagnose the leakage of the particular injector that is to be tested if during said third observation time window the engine speed exceeds a calibration threshold which is greater than the values of the engine speed if the injector is leak-tight.