Method and apparatus for controlling a capacitive actuator

A method for controlling a piezoelectric actuator for a fuel injection valve of an internal combustion engine, which comprises:

• determining an energy applied to an actuator;
• measuring an actuator voltage present at the actuator;
• and
• inferring a functional state of the actuator by using the energy and the actuator voltage.

A circuit for controlling a capacitive actuator, the circuit comprising:

• a driving circuit having:
• a main switch;
• a charging capacitor connected to an energy source through said main switch;
• a first series circuit parallel to said charging capacitor, said first series circuit including:
• an oscillating coil connected to said main switch;
• an auxiliary switch;
• and
• a second series circuit parallel to said auxiliary switch, said second series circuit having:
• a parallel circuit including a discharging switch and a charging switch, and
• another circuit including a diode to be connected in parallel to the actuator conducting in a direction to ground;
• and
• a control device for driving said driving circuit, said control device receiving input signals and having a program and a family of characteristics with:
• actuator characteristics defining characteristic curves;
• reference values;
• and
• correction factors compensating for temperature and for losses of said driving circuit,
• said control device controlling said main switch, said auxiliary switch, said charging switch, and said discharging switch with said program dependent upon the input signals and upon said characteristic curves of said family of characteristics, the input signals including at least one of:
• actuator voltage;
• actuator temperature;
• at least one measured variable;
• and
• a driving signal.

A configuration for controlling a piezoelectric actuator for a fuel injection valve of an internal combustion engine, comprising:

• a driving circuit having:
• a main switch;
• a charging capacitor connected to an energy source through said main switch;
• a first series circuit parallel to said charging capacitor, said first series circuit including:
• an oscillating coil connected to said main switch;
• an auxiliary switch;
• and
• a second series circuit parallel to said auxiliary switch, said second series circuit having:
• a parallel circuit including a discharging switch and a charging switch, and
• another circuit including a diode to be connected in parallel to the actuator conducting in a direction to ground;
• and
• a control device for driving said driving circuit, said control device receiving input signals and having a program and a family of characteristics with:
• actuator characteristics defining characteristic curves;
• reference values;
• and correction factors compensating for temperature and for losses of said driving circuit,
• said control device controlling said main switch, said auxiliary switch, said charging switch, and said discharging switch with said program dependent upon the input signals and upon said characteristic curves of said family of characteristics, the input signals including at least one of:
• actuator voltage;
• actuator temperature;
• at least one measured variable;
• and
• a driving signal.