Piezo Actuator Insulation Compression for Fuel Injector Heat Dissipation
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Solution Overview
Problem
Piezo actuators in fuel injectors face challenges with high electrical losses leading to increased temperatures, exceeding the permissible temperature limit, and the need for improved heat dissipation and centering within restricted installation spaces, especially with high actuator strokes and thermal differences.
Innovation Solution
A piezo actuator design featuring a piezo layer stack surrounded by an insulation layer with a prestressing device, where the insulation layer's outer diameter is greater than the prestressing device's inner diameter, allowing for defined compression and heat dissipation, and a wave spring configuration for both pretensioning and sealing, with a three-dimensional surface structure for simplified assembly and enhanced heat transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the piezo actuator uses a traditional separate membrane and spring design for sealing and prestressing, then the sealing function is achieved, but the heat dissipation capability is insufficient and the assembly complexity increases
Solution Approach 1:
The patent combines the sealing membrane and prestressing spring into a single integrated component where the membrane itself provides both sealing and prestressing functions. The membrane is pre-tensioned during assembly to create both the seal and the necessary prestress on the piezo stack, eliminating the need for separate spring and membrane components.
Solution Approach 2:
The membrane is designed to serve multiple functions simultaneously: it acts as a seal to prevent fuel leakage, provides prestressing force on the piezo stack through pre-tensioning, and serves as a thermal management pathway by conducting heat away from the piezo actuator. This multi-functional design reduces overall system complexity.
2Productivity
If the piezo actuator increases the number of injection cycles to meet future fuel injection requirements, then the productivity is improved, but the electrical losses increase causing excessive temperature rise
Solution Approach 1:
The patent converts the harmful effect of electrical losses (heat generation) into a beneficial thermal management system. The membrane and housing are designed with intentional thermal conduction pathways that use the heat generated during high-frequency injection cycles to warm the surrounding fuel, improving fuel temperature and reducing viscosity for better atomization, while preventing excessive temperature buildup in the piezo actuator itself.
3Temperature
If the insulation layer outer diameter is made equal to or smaller than the prestressing device inner diameter for easy assembly, then the ease of manufacture is improved, but the heat dissipation capability and centering precision are reduced
Solution Approach 1:
The patent utilizes thermal expansion parameter changes to resolve the assembly contradiction. The insulation layer is designed with an outer diameter slightly larger than the prestressing device inner diameter at room temperature, creating a interference fit that provides precise centering and optimal heat dissipation contact. During assembly, the thermal expansion and contraction of materials at operating temperatures maintains the fit without excessive assembly force, while the controlled interference ensures thermal contact for heat dissipation.
4Strength
If the piezo actuator uses a rigid connection for the prestressing device to ensure structural stability, then the strength is improved, but the thermal expansion differences cause excessive stresses
Solution Approach 1:
The patent accounts for thermal expansion differences between materials by designing the prestressing device and housing with compatible thermal expansion coefficients or by incorporating expansion compensation mechanisms. The membrane material is selected to have thermal expansion properties that match the housing, reducing differential thermal stresses during temperature cycles while maintaining structural stability through the pre-tensioned membrane design.
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 design effectively manages heat dissipation, maintains the piezo actuator within permissible temperature limits, and ensures precise centering of the piezo layer stack, even under high thermal loads and increased injection cycles, while preventing damage from excessive forces during assembly.
Implementation Method 1
the outside diameter of the insulation layer is greater than the inside diameter of the pretensioning device, so that in an assembled state the insulation layer is pressed in the pretensioning device... working heat generated during operation of the piezo actuator can be dissipated to the environment via the contact between the insulation layer and the prestressing device
Implementation Method 2
Piezo actuators that are used in fuel injectors are preloaded with a force that is dependent on the cross section of a piezo layer stack arranged in the piezo actuator
Data Source
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AI summary
The invention relates to a piezo actuator (30) for a fuel injector (10), comprising: a piezo layer stack (14) having a longitudinal extension (32); and an insulation layer (44) surrounding the piezo layer stack (14) The insulation layer (44) has an insulation layer outer surface (58), facing away from the piezo layer stack (14), which defines an outer diameter (54) of the insulation layer (44). In addition, a preloading device (46) for preloading the piezo layer stack (14) is also provided along the longitudinal extension (32), wherein the preloading device (46) has a preloading device inner surface (60), facing towards the piezo layer stack (14), which defines an inner diameter (56) of the preloading device (46). In a non-assembled state, the outer diameter (54) of the insulation layer (44) is greater than the inner diameter (56) of the preloading device (46), such that, in an assembled state, the insulation layer (44) is compressed in the preloading device (46). The invention also relates to a fuel injector (10) having said piezo actuator (30).