Method and device for driving at least one capacitive actuator

Abstract

In a driving operation, a capacitive actuator is charged from a series circuit of two capacitors having a charging voltage. An actuator voltage established at the actuator is controlled to a prescribed desired value in a course of a subsequent driving operation; the same procedure occurs for further actuators.

We claim:  
     
       1. A method for driving at least one capacitive actuator, including a piezoelectrically operated fuel injection valve of an internal combustion engine, which comprises: 
       charging, at a start of a driving operation, an actuator of a plurality of actuators with a prescribable charging voltage via a coil from a series circuit composed of a charging capacitor and a charge-reversing capacitor, and discharging the actuator into the charge-reversing capacitor at an end of the driving operation;  
       comparing an actuator voltage of the actuator due to the prescribable charging voltage with a prescribed desired-value voltage;  
       determining a new charging voltage for a next driving operation in dependence on a difference between the prescribed desired-value voltage and the actuator voltage; and  
       charging the charging capacitor for the next driving operation to a voltage corresponding to a difference between the new charging voltage and a voltage present across the charge-reversing capacitor.  
     
     
       2. The method according to  claim 1 , which comprises setting at a start of the driving operation a prescribed value for the prescribable charging voltage for each of the plurality of actuators. 
     
     
       3. The method according to  claim 2 , which comprises setting the prescribed value for the prescribable charging voltage in dependence on an engine temperature. 
     
     
       4. A device for driving at least one capacitive actuator, comprising: 
       a voltage source having a positive pole and a negative pole;  
       a charging capacitor disposed between said positive pole and said negative pole;  
       a control circuit controlling said voltage source;  
       a first series circuit disposed parallel to said charging capacitor and containing a charging switch connected to said positive pole for conducting current away from said positive pole and a discharging switch connected to said negative pole for conducting current toward said negative pole;  
       a ground terminal;  
       a second series circuit disposed between a connection point of said charging switch and said discharging switch and said ground terminal, said second series circuit containing a charge reversing capacitor having a recharge voltage connected to said charging switch and a coil;  
       at least one third series circuit connected in series with said second series circuit and containing an actuator having an actuator voltage and a controlled Power-MOSFET-switch; and  
       a diode disposed parallel to said at least one third series circuit and conducting from said ground terminal to said coil.  
     
     
       5. The device according to  claim 4 , wherein said voltage source is a switched-mode power supply. 
     
     
       6. The device according to  claim 4 , wherein said control circuit is a part of a microprocessor-controlled engine control unit, said control circuit being fed as input variables control signals for driving said actuator, said actuator voltage present at a respectively driven actuator and said recharge voltage present across said charge-reversing capacitor, said control circuit further controlling said charging switch, said discharging switch and said Power-MOSFET-switch for charging and discharging said actuator. 
     
     
       7. The device according to  claim 4 , wherein said charging switch and said discharging switch are electronic semiconductor switches passing current only in one direction. 
     
     
       8. The device according to  claim 4 , wherein said at least one third series circuit is a plurality of third series circuits disposed parallel to each other and all in series with said second series circuit.