Diesel common-rail piezo-operated servo injector

1. A method for operating a diesel-common-rail piezo-operated servo injector in which a piezo-actuator opens and closes a nozzle needle by means of a servo valve, the method comprising:

partially charging the piezo-actuator from a non-charged state at 0 V (method a);

partially discharging the piezo-actuator from an already charged state to a remaining limited charge (method b);

measuring the piezo-voltage with both methods and comparing the results;

determining a voltage for the piezo-actuator for each operating point so that the piezo-actuator applies a force necessary for contact with the servo valve without influencing the injection process itself by opening the servo valve;

when the comparison demonstrates correspondence within a predefined threshold, using method b in ranges in which method a cannot be carried out; and

when the comparison does not demonstrate correspondence within the predefined threshold, using method a without using method b.

2. The method as claimed in claim 1 , further comprising switching to and fro between method a and method b during a specific injection process throughout one engine cycle.

3. The method as claimed in claim 1 , further comprising measuring the force during a specific main injection.

4. The method as claimed in claim 1 , further comprising measuring the force during times at which no large change of the operating point takes place.

5. The method as claimed in claim 1 , further comprising carrying out the partial discharging of the piezo-actuator (method b) starting from a charged state of said piezo-actuator associated with an actual injection.

6. The method as claimed in claim 1 , further comprising executing the partial charging (method a) after complete discharging of the piezo-actuator.

7. A motor vehicle comprising:

a combustion chamber;

a diesel-common-rail piezo-operated servo injector operating to inject fuel into the combustion chamber; and

a control unit programmed to:

partially charge the piezo-actuator from a non-charged state at 0 V (method a);

partially discharge the piezo-actuator from an already charged state to a remaining limited charge (method b);

measure the piezo-voltage with both methods and comparing the results;

determine a voltage for the piezo-actuator for each operating point so that the piezo-actuator applies a force necessary for contact with the servo valve without influencing the injection process itself by opening the servo valve;

when the comparison demonstrates correspondence within a predefined threshold, use method b in ranges in which method a cannot be carried out; and

when the comparison does not demonstrate correspondence within the predefined threshold, use method a without using method b.