Piezo Stack Zero Point Correction via Regeneration Voltage
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Solution Overview
Problem
Piezoelectric stacks used in fuel injectors experience depolarization due to operating field strengths lower than the poling field, leading to changes in length that impair engine function, requiring complex compensation methods to maintain a stable zero point position.
Innovation Solution
A method to control piezoelectric actuators by monitoring deviations in length and applying a higher field strength than used during poling to actively correct the zero point position, eliminating the need for hydraulic play compensation and reverse polarity circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the piezo stack is operated with a field strength smaller than the poling field strength, then the piezo stack can perform regular actuation operations, but depolarization occurs over time causing change in length and zero point position deviation
Solution Approach 1:
The patent applies periodic regeneration voltage pulses at intervals of 10 to 1000 seconds during regular operation to counteract depolarization. This periodic action maintains the zero point position without interrupting normal actuation operations, resolving the contradiction between ease of operation and position stability.
Solution Approach 2:
The patent changes the field strength parameter by applying regeneration voltage (equal to or greater than the coercive field strength) temporarily to repolarize the piezo material, then returns to normal operating field strength. This parameter change restores the zero point position while maintaining operational ease.
2Reliability
If hydraulic play compensators or reverse polarity circuits are used to maintain zero point position, then position stability is improved, but device complexity increases
Solution Approach 1:
The control unit uses the existing piezoelectric actuator components and integrated sensors to detect and correct zero point deviations through regeneration voltage application. This self-service approach eliminates the need for external hydraulic compensators or complex reverse polarity circuits, maintaining position stability while reducing device complexity.
Solution Approach 2:
The patent implements a feedback mechanism where the control unit continuously monitors the zero point position and automatically applies regeneration voltage when deviations are detected. This closed-loop feedback system maintains position stability using simple control logic rather than complex hardware circuits.
3Duration of action of moving object
If the piezo stack is operated continuously without regeneration, then operational duration is extended, but the change in length due to depolarization accumulates and impairs function
Solution Approach 1:
The patent applies periodic regeneration voltage pulses at intervals of 10 to 1000 seconds during regular operation to counteract depolarization. This periodic action maintains the zero point position without interrupting normal actuation operations, resolving the contradiction between ease of operation and position stability.
Solution Approach 2:
The patent changes the field strength parameter by applying regeneration voltage (equal to or greater than the coercive field strength) temporarily to repolarize the piezo material, then returns to normal operating field strength. This parameter change restores the zero point position while maintaining operational ease.
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 enables a physical correction of the zero point position without requiring hydraulic play compensation or complex circuits, ensuring reliable operation and maintaining the desired length of the piezoelectric stack during regular operation.
Implementation Method 1
A piezoelectric stack is a component that performs mechanical movement when an electrical voltage is applied
Implementation Method 2
Operating the piezo stack in regular operation with a field strength that is less than the field strength during a poling process causes a depolarization (reorientation) of the dipole moments over time, which are also referred to as domains. The same effect occurs when the piezo stack is exposed to changing temperatures, even when there is no electrical field. This effect leads to a change in length of the piezo stack.
Data Source
Figure 1~2
AI summary
The invention describes a method for driving a piezoelectric actuator with a piezoelectric stack (1), which is operated in particular as an actuating element of an injector. During its production, the piezoelectric stack (1) has been polarized by a polarization process initially with a first field strength (VPol), which results in a first length (Li) of the piezoelectric stack (1). In the method according to the invention, the piezoelectric stack (1) is driven, during operation, at a second field strength (VOp), which is smaller than the first field strength (VPol), wherein a setpoint length (SL) for the piezoelectric stack (1) is defined depending on the second field strength (VPol). In addition, a change in length caused by depolarization from the setpoint length (SL) of the piezoelectric stack (1) is monitored. Then, when a predetermined threshold value (SW) for the change in length is reached, the piezoelectric stack (1) is operated at a third field strength (VCor) until the setpoint length (SL) for said piezoelectric stack (1) is reached.