Method and device for control of a capacitive actuator
View Patent ↗A piezoelectric actuator on an injection valve is controlled by application of a control curve, on which the maximum amplitudes for a current for controlling the actuator are given. A slowly rising or falling charge course at the beginning or end of a charging or discharging process and hence a linearly controllable charge level can thus be achieved over time. An overdriving of the actuator can thus be prevented.
1. A method for controlling an actuator, including a piezoelectric actuator, which comprises the steps of:
charging or discharging the actuator in at least three stages, each of the three stages having a defined duration of a current further defined by the steps of:
during a first duration, increasing a maximum amplitude of the current from a predefined minimum to a predefined first maximum;
during a second duration, keeping the maximum amplitude of the current substantially constant;
during a third duration, lowering the maximum amplitude of the current from a further predefined maximum to a further predefined minimum; and
adjusting an amount of charge for charging and discharging the actuator by adjusting the second duration.
2. The method according to claim 1 , which further comprises selecting the first maximum in accordance with an amount of charge to be fed to the actuator.
3. The method according to claim 1 , which further comprises selecting the second duration in accordance with an amount of charge to be fed to the actuator.
4. The method according to claim 2 , which further comprises reading out the first maximum and/or the second duration depending on a predefined length change from a characteristic data field.
5. The method according to claim 1 , wherein the maximum amplitudes lie on an envelope curve which, over the first, second and third durations has substantially a shape of a trapeze.
6. The method according to claim 1 , which further comprises providing the current to be intermittent.
7. The method according to claim 1 , which further comprises forming the current to be made up of a series of pulses, with a maximum amplitude corresponding in each case to the maximum current of the relevant pulse.
8. The method according to claim 7 , which further comprises forming the pulses in triangular shapes.
9. The method according to claim 1 , wherein amplitudes of the current increase without pausing after a predefined minimum has been reached.
10. The method according to claim 1 , wherein the current is provided by a final stage depending on a control voltage, with the control voltage being provided by a digital-analog converter.
11. A device for controlling an actuator, including piezoelectric actuators, the device comprising:
a final stage having a control input; and
a control unit providing a control voltage to operate said final stage, the control voltage rising during a first time period from a predefined minimum to a predefined maximum, remaining constant during a second time period and falling during a third time period from a further predefined maximum to a predefined final value; and
said control unit adjusting a charge for operating the actuator by adjusting a length of the second time period.
12. The device according to claim 11 , wherein said control unit has a digital-analog converter providing the control voltage.