Method and device for repolarizing a piezoelectric actuator of an injector of an internal combustion engine of a used vehicle

1. A method for repolarizing a piezoelectric actuator of an injector of an internal combustion engine of a used vehicle, said piezoelectric actuator having undergone initial polarization before the vehicle was put into use, characterized in that the method comprises the following steps, the piezoelectric actuator being associated with the injector, and the injector being mounted on the engine, the engine being stopped:

ensuring that a residual injector fuel supply pressure is less than a specified threshold below which no injection of fuel into the combustion chamber can take place;

applying a first polarization voltage (V 1 ) to the terminals of the piezoelectric actuator during a first specified time interval (T 1 ) of not less than ten minutes;

stopping the application of the first polarization voltage (V 1 ) during a second time interval (T 2 ), following the first time interval (T 1 ) and at least equal to the latter, thus defining a pause time in which no voltage is applied to the actuator terminals;

applying a second polarization voltage (V 2 ) to the terminals of the piezoelectric actuator during a third specified time interval (T 3 ), following the second time interval; and

stopping the application of the second polarization voltage (V 2 ) to the terminals of the piezoelectric actuator after the third time interval (T 3 ),

said first (T 1 ), second (T 2 ) and third (T 3 ) successive time intervals, in combination, defining a repolarization sequence of the piezoelectric actuator.

2. The method according to claim 1 , wherein the pause time is between one and three times the first (T 1 ) or the third (T 3 ) time interval.

3. The method according to claim 2 , wherein the first time interval (T 1 ) is in the range from 30 to 45 minutes.

4. The method according to claim 2 , wherein the third time interval (T 3 ) is equal or approximately equal to the first time interval (T 1 ).

5. The method according to claim 2 , wherein the first polarization voltage (V 1 ) and the second polarization voltage (V 2 ) are about 160 volts each.

6. The method according to claim 2 , wherein the first (V 1 ) and second (V 2 ) polarization voltages are applied by means of the vehicle battery, via a voltage step-up means, said method further comprising a step of ensuring that the voltage of said battery is above a predetermined voltage threshold before the first voltage (V 1 ) is applied to the terminals of the piezoelectric actuator during the first specified time interval (T 1 ).

7. The method according to claim 2 , wherein the time interval for the application of the first (V 1 ) or second (V 2 ) polarization voltage comprises a cycle of successive voltage pulses (Imp), each of said electrical pulses having a duration (t i ) in the range from 5 milliseconds to several seconds.

8. The method according to claim 7 , wherein each of said electrical pulses has a duration (t i ) in the range from 10 to 100 milliseconds.

9. The method according to claim 2 , characterized in that the first polarization voltage (V 1 ), the pause time, and the second polarization voltage (V 2 ) are respectively applied to all the piezoelectric actuators of the engine.

10. The method according to claim 1 , wherein the first time interval (T 1 ) is in the range from 30 to 45 minutes.

11. The method according to claim 1 , wherein the third time interval (T 3 ) is equal or approximately equal to the first time interval (T 1 ).

12. The method according to claim 1 , wherein the first polarization voltage (V 1 ) and the second polarization voltage (V 2 ) are about 160 volts each.

13. The method according to claim 1 , wherein the first (V 1 ) and second (V 2 ) polarization voltages are applied by means of the vehicle battery, via a voltage step-up means, said method further comprising a step of ensuring that the voltage of said battery is above a predetermined voltage threshold before the first voltage (V 1 ) is applied to the terminals of the piezoelectric actuator during the first specified time interval (T 1 ).

14. The method according to claim 1 , wherein the time interval for the application of the first (V 1 ) or second (V 2 ) polarization voltage comprises a cycle of successive voltage pulses (Imp), each of said electrical pulses having a duration (t i ) in the range from 5 milliseconds to several seconds.

15. The method according to claim 14 , characterized in that it consists, during the first (T 1 ) or third (T 3 ) time interval, in applying said successive voltage pulses to all the piezoelectric actuators of the engine, so that the successive voltage pulses (Imp) applied to a given injector are separated by a rest time (tp i ) corresponding to the application time of the successive voltage pulses to each of the other piezoelectric actuators.

16. The method according to claim 14 , wherein each of said electrical pulses has a duration (t i ) in the range from 10 to 100 milliseconds.

17. The method according to claim 1 , characterized in that the first polarization voltage (V 1 ), the pause time, and the second polarization voltage (V 2 ) are respectively applied to all the piezoelectric actuators of the engine.

18. A device for repolarizing a piezoelectric actuator of an injector of an internal combustion engine of a used vehicle, said piezoelectric actuator having undergone initial polarization before the vehicle was put into use, the piezoelectric actuator being associated with the injector, the engine being stopped, and the injector being mounted on the engine and in communication with an engine control unit of the engine, the device comprising:

an electronic maintenance box in electrical connection with the engine control unit,

said electrical connection to the engine control unit being configured to enable the electronic maintenance box to activate and control the engine control unit, and

said electronic maintenance box being configured to execute software, implemented in said electronic maintenance box that upon execution by the electronic maintenance box causes the engine control unit, via said electrical connection to the engine control unit to perform the functions of

ensuring that a residual injector fuel supply pressure, via a fuel supply pressure sensor associated with the injector, is less than a specified threshold below which no injection of fuel into the combustion chamber can take place,

applying a first polarization voltage (V 1 ) to the terminals of the piezoelectric actuator during a first specified time interval (T 1 ) of not less than ten minutes,

stopping the application of the first polarization voltage (V 1 ) during a second time interval (T 2 ), following the first time interval (T 1 ) and at least equal to the latter, thus defining a pause time in which no voltage is applied to the actuator terminals,

applying a second polarization voltage (V 2 ) to the terminals of the piezoelectric actuator during a third specified time interval (T 3 ), following the second time interval, and

stopping the application of the second polarization voltage (V 2 ) to the terminals of the piezoelectric actuator after the third time interval (T 3 ),

said first (T 1 ), second (T 2 ) and third (T 3 ) successive time intervals, in combination, defining a repolarization sequence of the piezoelectric actuator.