Device and Method for Triggering a Piezo Actuator

• US 20080088262A1
• Filed: 07/20/2005
• Published: 04/17/2008
• Est. Priority Date: 10/01/2004
• Status: Abandoned Application

• Current Assignee: Siemens AG
• Original Assignee: Siemens AG
• Inventors: Bolz, Stephan
• Application Number:
  US11/664,492
• Publication Number:
  US 20080088262A1
• Time in Patent Office: Days
• US Class Current: 318/116
• CPC Class Codes: F02D 2041/2003 using means for creating a boost voltage, i.e. generation or use of a voltage higher than the battery voltage, e.g. to speed up injector opening
• CPC Class Codes: F02D 2400/14 Power supply for engine control systems
• CPC Class Codes: F02D 41/2096 for controlling piezoelectric injectors drive and control circuit for piezoelectric devices in general H10N30/802
• CPC Class Codes: F02D 41/221 relating to the failure of actuators or electrically driven elements
• CPC Class Codes: H02N 2/067 generating drive pulses

Abstract

A device and a method trigger a piezo actuator by use of a DC/DC converter supplying a supply voltage at the output end, the supply voltage is applied to a series connection encompassing a high-side switching transistor and a low-side switching transistor. A series connection containing a high inductance coil and the piezo actuator that is to be triggered is disposed between the junction of the two switching transistors and a reference potential. An excitation signal having a predefined pulse duty factor (effective voltage) and a predefined switching frequency is applied to the junction in order to charge or discharge the piezo actuator.

Claims

1-11. -11. (canceled)

12. A device for triggering a piezo actuator, the device comprising:

a DC/DC converter receiving a vehicle electrical system voltage, said DC/DC converter having an output delivering a high supply voltage;

an intermediate circuit capacitor;

a first series circuit disposed in parallel to said intermediate circuit capacitor and formed of a high-side switching transistor and a low-side switching transistor disposed between said output of said DC/DC converter and a reference potential, a connection point between said high-side switching transistor and said low-side switching transistor defining a connection junction;

a driver circuit receiving a control signal connected to and controlling said first series circuit; and

a coil of high inductance connected to said connection junction, said coil and the piezo actuator to be triggered defining a second series circuit disposed between said connection junction of said high and low side switching transistors and the reference potential.

13. A method for operating a device for triggering a piezo actuator, the device containing:

a DC/DC converter receiving a vehicle electrical system voltage, the DC/DC converter having an output delivering a high supply voltage;

an intermediate circuit capacitor;

a first series circuit disposed in parallel to the intermediate circuit capacitor and formed of a high-side switching transistor and a low-side switching transistor disposed between the output of the DC/DC converter and a reference potential, a connection point between the high-side switching transistor and the low-side switching transistor defining a connection junction;

a driver circuit receiving a control signal controlling the first series circuit; and

a coil of high inductance connected to the connection junction, the coil and the piezo actuator to be triggered defining a second series circuit disposed between the connection junction of the high and low side switching transistors and the reference potential;

the method which comprises the steps of;

applying an excitation signal to the connection junction by means of an inverse switching processes of the high-side and low-side switching transistors for charging to a desired actuator voltage or for discharging the piezo actuator, the excitation signal having an effective voltage corresponding to around half a value of the desired actuation voltage; and

forming the excitation signal from a product of the high supply voltage and a pulse duty ratio, with the pulse duty ratio corresponding to a temporal relationship of a conducting phase and a non-conducting phase of the high-side switching transistor or a temporal relationship of conducting phases of the high-side and low-side switching transistors, the excitation signal having a predeterminable switching frequency for the triggering of the high-side and low-side switching transistors.

14. The method according to claim 13, which further comprises applying the excitation signal until a charging current or a discharging current becomes zero.

15. The method according to claim 13, which further comprises providing the predeterminable switching frequency in a range of 50 kHz for activation of the high-side and low-side switching transistors.

16. The method according to claim 13, which further comprises changing at least one of the pulse duty ratio, a switching duration and inserted operating phases, for obtaining voltage levels of the desired actuator voltage in any given curve, including part lifts.

17. The method according to claim 13, which further comprises:

determining an amount of energy E fed to the piezo actuator from a capacitance Cp of the piezo actuator and the desired actuator voltage Up according to formula

E=½

*Cp*Up²,

determining the capacitance Cp of the piezo actuator from a size of an inductance of the coil and a reciprocal oscillation frequency ω

for a ring-around duration T_umschwing, where

ω

=1/√

L*Cp, T=2*π

/ω and

T=2*T_umschwing

and

Cp=T²_umschwing/(π

²*L).

18. The method according to claim 17, which further comprises taking into account a resistance value of actuator impedance and further loss factors in the determining of the capacitance Cp of the piezo actuator.

19. The method according to claim 18, which further comprises detecting an actual value of the inductance of the coil by performing a production calibration and storing the actual value for calculating the actuator capacitance Cp.

20. The method according to claim 19, which further comprises jointly considering the actuator impedance, the further loss factors and actual value of the inductance of the coil for the determining the actuator capacitance Cp.

21. The method according to claim 13, which further comprises:

measuring an amount of energy fed to the piezo actuator during a charge process resulting in measured energy;

comparing the measured energy to a predetermined amount of energy; and

correcting for differences between the measured energy and the predetermined amount of energy resulting from temperature-induced changes to the capacitance Cp of the piezo actuator by changing the pulse duty ratio in a next charging process.

22. The method according to claim 13, which further comprises detecting one of a short circuit and a line break in a charge path, if the desired actuator voltage measured during a charge process after a completed switching pulse lies outside a predefined voltage window assigned to a reference value.