Fuel Cell Tie Rod - Shape Memory Alloy
Publication Date: 2002-Mar-27
The IP.com Prior Art Database
Fuel Cell Tie Rods are made from a shape memory alloy. These function as a load follow up system to maintain a desired compressive force on the fuel cell stack.
FUEL CELL TIE ROD LOAD FOLLOW-UP
A fuel cell stack may be held together with tie rods under tension that extend from one end of the stack to the other. The force applied to the stack by the tie rods can vary depending upon the size and the type of fuel cell, the types of seals used between the individual fuel cells, etc. The tie rods preferably apply a constant load during the life of the stack. Unfortunately, the stack can settle/compact under the influence of the applied load, causing the load to decrease over time. To counter-act this settling effect, a “load follow-up system” may be used.
One type of load follow-up system utilizes one or more belleville washers at either or both ends of stainless steel tie rods. Nuts screwed onto the ends of the tie rods hold the washers in place and resiliently compress them against the end plates in the stack. The washers function as a compressed spring to accommodate settling in the stack and maintain the applied load. This system can involve a large number of parts that increases the complexity, assembly time, and cost of a fuel cell stack. Moreover, experience has indicated that the belleville washer system may allow the loads applied to the stack to decrease over time.
An alternative load follow-up system uses tie rods made out of a shape memory alloy (SMA) such as nickel-titanium (Nitinol). These types of load follow-up systems rely on the super elastic properties of SMA’s to maintain a constant load against the stack, so t...