Control method and apparatus for a piezoelectric injector

摘要

A control method for a fuel injector having a piezoelectric stack (14) which is charged by means of a charge current (I charge ) and discharged by means of a discharge current (I discharge ) comprises determining a required separation time (t demand ) between the end of an electrical on signal associated with a first injection event (IE1) and the beginning of an electrical on signal associated with a second injection event (IE2). The control method also comprises calculating an overlap time (t overlap ) between the required separation time (t demand ) and the time required to charge the piezoelectric stack (14) to a first reference level using the charge current; dividing the overlap time (t overlap ) into first and second time periods (t overlap_portion1, t overlap_portion2 ) as a function of the charge and discharge currents (I charge , I discharge ); applying the charge current (I charge ) to the piezoelectric stack (14) for a charge time (t charge ) calculated on the basis of the first time period of the overlap time (t overlap_portion1 ); and applying the discharge current (I discharge ) to the piezoelectric stack (14) for a discharge time (t discharge ) so as to discharge the stack (14) to a second reference level, wherein the discharge time is calculated on the basis of the second time period of the overlap time (t overlap_portion2 ). As a result, the first and second injection events (IE1, IE2) are merged in a merging pulse mode of operation.