Method for controlling the injection quantity of a piezoinjector of a fuel injection system

1. A method for controlling an injection quantity of a piezoinjector of a fuel injection system, the piezoinjector having a piezo actuator and a nozzle needle which can be moved by the piezo actuator, the method comprising:

receiving, at a switch, a signal indicating an instantaneous injection quantity,

determining, by the switch, an instantaneous injection quantity based on the received signal, and

automatically switching, by the switch, between a first and a second control method as a function of the instantaneous injection quantity,

wherein the first control method includes setting a needle closing time to a reference closing time value and a needle flight time to a reference flight time value, and

the second control method includes setting only the needle closing time to the reference closing time value.

2. The method of claim 1 , comprising:

performing a first control method in a ballistic injector operating mode in which small injection quantities occur because the nozzle needle is only partially open, and

performing a second control method in a full stroke injector operating mode in which large injection quantities occur because the nozzle needle is fully open.

3. The method of claim 1 , comprising:

using a PI controller during the execution of the first control method, and

using a P controller during execution of the second control method.

4. The method of claim 1 , comprising implementing a chronological change of the starting time of the electrical actuation of the piezoelectric actuator during the execution of the first control method.

5. The method of claim 4 , comprising implementing the chronological change in the starting time of the electrical actuation of the piezoelectric actuator such that the needle flight time corresponds to a reference needle flight time.

6. The method of claim 5 , comprising determining the reference needle flight time using a reference piezoinjector, wherein data describing the reference needle flight time is stored in a non-volatile fashion in a memory.

7. The method of claim 1 , comprising implementing a chronological change in the needle closing time during the execution of the second control method.

8. The method of claim 7 , comprising implementing the chronological change in the needle closing time such that the needle closing time corresponds to a reference needle closing time.

9. The method of claim 8 , comprising determining the reference needle closing time using a reference piezoinjector, and wherein data describing the reference needle closing time is stored in a non-volatile fashion in a memory.