Piezo-Actuator Calibration via Impedance Spectroscopy
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Solution Overview
Problem
Piezoelectric actuators in automotive systems exhibit nonlinear and hysteresis-affected behavior, making precise control challenging due to temperature and load dependencies, and existing calibration methods are complex, costly, and not suitable for real-world usage conditions, especially in large-signal operating modes.
Innovation Solution
A method and device for calibrating piezoelectric actuators in motor vehicles involve applying an electrical calibration pulse in the large-signal range with varying frequency to determine the impedance profile, allowing for the derivation of nonlinear material coefficients and adaptation of control parameters, enabling precise control and monitoring of the actuator's behavior.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If linear regulation concepts with constant piezoelectric module assumption are used, then device complexity is reduced, but manufacturing precision deteriorates due to high manufacturing tolerances and temperature/pressure dependencies
Solution Approach 1:
The patent applies parameter changes by transitioning from constant material coefficients to dynamic, operating-point-dependent material coefficients. The system continuously adapts the piezoelectric module dij, elastic module cE, and dielectric constant eS based on measured temperature, pressure, and voltage conditions, enabling precise control despite manufacturing tolerances and environmental variations.
Solution Approach 2:
The patent implements feedback mechanisms by measuring actual operating conditions (temperature, pressure, voltage) and using these measurements to continuously update the material coefficients in the control model. This closed-loop approach compensates for deviations caused by manufacturing tolerances and environmental changes, maintaining high injection precision.
2Measurement precision
If impedance spectroscopy measurement methods are used to determine material coefficients, then measurement precision is improved, but device complexity and cost increase due to complex hardware requirements
Solution Approach 1:
The patent applies self-service by using the existing control circuitry and output stage of the piezoelectric actuator system to perform impedance measurements. The control circuit generates calibration pulses and measures impedance without requiring separate dedicated measurement hardware, thereby achieving precise material coefficient determination while avoiding increased device complexity and cost.
Solution Approach 2:
The patent implements multi-functionality by enabling the control circuit to serve dual purposes: normal actuator control and impedance measurement for material coefficient determination. The same hardware components are used for both control signal generation and impedance spectroscopy, eliminating the need for separate measurement systems.
3Use of energy by moving object
If small-signal measurements are used to determine material coefficients, then use of energy is reduced, but measurement precision deteriorates due to inability to capture large-signal operating conditions
Solution Approach 1:
The patent applies dynamics by transitioning from static small-signal measurements to dynamic large-signal measurements that capture the actual operating conditions. The system performs impedance measurements using calibration pulses that reflect real operating voltages and frequencies, enabling accurate determination of material coefficients under large-signal conditions while managing energy consumption through controlled measurement timing.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for precise calibration and control of piezoelectric actuators in real-world conditions, improving the accuracy of injection operations and fluid metering, even under varying temperature and load conditions, by determining nonlinear material coefficients and adapting control parameters based on impedance profiles.
Implementation Method 1
Piezoelectric actuators are used in the automotive industry above all as final control elements for metering devices... Piezoelectric actuating elements are also used increasingly in other sectors of the automotive industry... Modern injection elements, such as are used e.g. in common-rail or pump-injector systems, are already operated today with the aid of piezoelectric-controlled control valves
Implementation Method 2
However, said actuating elements also have disadvantages which are inherent in the nonlinear and hysteresis-affected behavior of the piezoelectric element itself... the behavior of complex components, such as piezoelectric-controlled injection valves, for which precise control is particularly important, cannot be adequately predicted under real-world usage conditions by means of a linear approach
Implementation Method 3
A method and device for calibrating piezoelectric actuators in motor vehicles involve applying an electrical calibration pulse in the large-signal range with varying frequency to determine the impedance profile... the frequency of said calibration pulse being varied over time, and the associated electrical impedance profile is determined via the frequency and evaluated
Data Source
AI summary
In a method for calibration, a piezo-actuator (1) is actuated in a motor vehicle by a control circuit and an output stage. The piezo actuator is, in particular, part of the injection valve. The piezo-actuator (1) is subjected to an electric calibration pulse that is in the high-level signal range thereof when the control circuit and the output stage are in operation, the frequency thereof being modified over time. The associated electric impendence curve over the frequency is determined and evaluated during the calibration pulse. The output stage is controlled by the control circuit in such a manner that the calibration pulse is generated.