Fuel Cell Stack Natural Frequency via Compression Straps
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Solution Overview
Problem
Fuel cell stacks in automotive applications are susceptible to damage from resonance due to low natural frequency caused by mechanical vibrations, which is exacerbated by high aspect ratios and increased cell count, leading to potential damage during vehicle motion.
Innovation Solution
Incorporating electrically insulating support bars between compression straps and the fuel cell stack, which apply a suitable tensile load to increase the natural frequency without significantly increasing weight or volume, using arc-shaped support bars with a thickness of 2.5 to 5 cm to distribute the load effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the number of fuel cells in the stack is increased to provide higher output voltage, then the power output is improved, but the natural frequency of the stack decreases making it more susceptible to resonance damage
Solution Approach 1:
The patent applies compression straps to pre-compress the fuel cell stack before operation, raising its natural frequency above the resonant frequency range of vehicle operational vibrations. This preliminary action prevents resonance damage before it can occur during vehicle operation, allowing the stack to safely handle higher power outputs with more cells.
2Reliability
If reinforcing plates are added to increase the natural frequency, then the resistance to resonance damage is improved, but the weight and volume of the stack increase
Solution Approach 1:
The patent changes the compression parameter by applying sufficient compressive force through the compression straps to raise the natural frequency of the stack. This parameter change achieves the reliability improvement without adding significant weight, as the compression mechanism uses existing structural components rather than adding heavy reinforcing plates.
Solution Approach 2:
The patent introduces compression straps as intermediary elements that apply compressive force to the stack. These straps act as mediators between the mounting structure and the fuel cells, distributing the compressive load and raising the natural frequency without requiring direct attachment of heavy reinforcing plates to each cell.
3Productivity
If the dimensions of individual cells are optimized for function with high aspect ratios, then the cell efficiency is improved, but the natural frequency of the stack decreases
Solution Approach 1:
The compression straps apply preliminary compressive force to the stack with high aspect ratio cells, raising the natural frequency to prevent resonance damage. This allows the cells to maintain their optimized functional dimensions without compromising structural reliability.
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
The natural frequency of the fuel cell stack is substantially increased to above 50 Hz, effectively preventing damage from resonance, as demonstrated by both calculated and experimental results, enhancing the stack's durability in automotive applications.
Implementation Method 1
at least one compression strap is provided adjacent the first side of the series stack, and at least one compression strap is provided adjacent the second side of the series stack. The opposing compression straps apply compression which urges the end plates together
Implementation Method 2
if the frequency of these vibrations is close to the natural frequency of the fuel cell stack, there is the possibility that the stack can resonate and be damaged as a result
Data Source
AI summary
In certain configurations and applications, fuel cell stacks can be subject to damage arising from resonance. For instance, the natural frequency of lengthy automotive fuel cell stacks can be low enough to be problematic. Incorporating appropriate support bars between the compression straps holding such stacks together and the fuel cells in the stack can suitably increase the natural frequency in a relatively compact manner.