Fuel cell stack having an integrated end plate assembly

1. A fuel cell stack ( 30 ) for producing electricity from reducing fluid and process oxidant reactant streams, the fuel cell stack ( 30 ) comprising:

a. a plurality of fuel cells ( 32 ) stacked adjacent each other to form a reaction portion ( 34 ) of the fuel cell stack ( 30 ), the plurality of fuel cells ( 32 ) including an end cell ( 36 ) at an outer end of the reaction portion ( 34 ) of the fuel cell stack ( 30 );

b. an integrated end plate assembly ( 38 ) secured adjacent the end cell ( 36 ), the assembly including;

i. a current collector ( 40 ) secured adjacent and in electrical communication with the end cell ( 36 );

ii. a pressure plate ( 42 ) secured adjacent the current collector and overlying the end cell ( 36 ), the pressure plate ( 42 ) defining a backbone-support plane ( 44 ) extending a distance from a center ( 46 ) of the pressure plate to between about thirty percent and about eighty percent of a distance between the center ( 46 ) of the pressure plate ( 42 ) and an exterior perimeter ( 48 ) of the pressure plate ( 42 ), and the pressure plate ( 42 ) defining a deflection plane ( 50 ) extending between the backbone-support plane ( 44 ) and the exterior perimeter ( 48 ) of the pressure plate ( 42 ), the deflection plane ( 50 ) also being between the backbone-support plane ( 44 ) and a contact surface ( 54 ) of the pressure plate ( 42 ) adjacent the current collector ( 40 );

iii. a backbone ( 60 ) including a plurality of tie-rod ends ( 62 , 64 , 66 , 68 ) defining throughbores ( 70 , 72 , 74 , 76 ) configured to receive and secure tie rods ( 78 , 80 ) adjacent a perimeter ( 48 ) of the pressure plate ( 42 ), the backbone ( 60 ) including at least one beam ( 82 ) extending between the tie-rod ends ( 62 , 64 , 66 , 68 ), the backbone ( 60 ) being secured adjacent the backbone-support plane ( 44 ) defined by the pressure plate ( 42 ), the backbone ( 60 ) also being secured adjacent a plurality of walls ( 56 A, 56 B, 56 C, 56 D) defined by the pressure plate ( 42 ), the plurality of walls ( 56 A, 56 B, 56 C, 56 D) extending adjacent at least two opposed sides of the beam ( 82 ) of the backbone ( 60 ) in a direction away from the current collector ( 40 ) a distance that is at least the same as a distance that the backbone ( 60 ) extends above the backbone-support plane ( 44 ) in a direction away from the current collector ( 40 ), and the backbone also configured to contact and extend along the backbone-support plane ( 44 ), and the tie-rod ends ( 62 , 64 , 66 , 68 ) of the backbone ( 60 ) configured to overlie the deflection plane ( 50 ) and define a gap ( 84 ) between the tie-rod ends ( 62 , 64 , 66 , 68 ) and the deflection plane ( 50 ), the backbone ( 60 ) configured to have adequate flexibility to permit expansion of the fuel cell stack ( 30 ) within operating dynamic limits of the stack ( 30 ) and having predetermined flexural strength to prohibit expansion of the stack ( 30 ) beyond the operating dynamic limits of the stack ( 30 ); and,

iv. the deflection plane ( 50 ) being defined within the pressure plate ( 42 ) a predetermined distance from the backbone-support plane ( 44 ) to permit flexure of the backbone ( 60 ) within the gap ( 84 ).

2. The fuel cell stack ( 30 ) of claim 1 , wherein the backbone-support plane extends a distance from the center ( 46 ) of the pressure plate to between about fifty percent and about sixty percent of a distance between the center ( 46 ) of the pressure plate ( 42 ) and an exterior perimeter ( 48 ) of the pressure plate ( 42 ).

3. The fuel cell stack ( 30 ) of claim 1 , wherein the beam ( 82 ) of the backbone ( 60 ) extends across the center ( 46 ) of the pressure plate ( 42 ).

4. The fuel cell stack ( 30 ) of claim 1 , wherein a maximum planar cross sectional area of the backbone ( 60 ) in a plane parallel to the contact surface ( 54 ) of the presure plate ( 42 ) is no greater than about fifty percent of a planer cross sectional area of the pressure plate ( 42 ) in a plane parallel to the contact surface ( 54 ) of the pressure plate ( 42 ).

5. A method of dynamically securing fuel cells ( 32 , 36 ) within the fuel cell stack ( 30 ) of claim 1 , comprising the steps of:

a. defining the backbone-support plane ( 44 ) within the pressure plate ( 42 ), the backbone-support plane ( 44 ) configured to extend a distance from the center ( 46 ) of the pressure plate ( 42 ) to between about thirty percent and about eighty percent of a distance between the center ( 46 ) of the plate ( 42 ) and an exterior perimeter ( 48 ) of the plate ( 42 ), and defining the deflection plane ( 50 ) within the pressure plate ( 42 ) extending between the backbone-support plane ( 44 ) and the exterior perimeter ( 48 ) of the pressure plate ( 42 ) and between the backbone-support plane ( 44 ) and the contact surface ( 54 ) of the pressure plate ( 42 );

b. securing the contact surface ( 54 ) of the pressure plate ( 42 ) adjacent the current collector ( 40 );

c. securing the current collector ( 40 ) adjacent the end cell ( 36 ) of the stack ( 30 );

d. securing the backbone ( 60 ) within the backbone-support plane ( 44 ) so that tie rod ends ( 62 , 64 , 66 , 68 ) of the backbone ( 60 ) extend over the deflection plane ( 50 ) defined within the pressure plate ( 42 ), and so that the plurality of walls ( 56 A, 56 B, 56 C, 56 D) are adjacent at least opposed sides of the beam ( 82 ) of the backbone ( 60 ) to prohibit lateral motion of the backbone ( 60 ) in any direction about parallel to a plane defined by the contact surface ( 54 ) of the pressure plate ( 42 ); and,

e. deflecting the tie rod ends ( 62 , 64 , 66 , 68 ) within the gap ( 84 ) defined between the tie rod ends ( 62 , 64 , 66 , 68 ) and the deflection plane ( 50 ) by tightening tie rods ( 78 , 80 ) within the tie rod ends ( 62 , 64 , 66 , 68 ) of the backbone ( 60 ).

6. A method of dynamically securing fuel cells ( 32 ) within the fuel cell stack ( 30 ) of claim 1 , comprising the steps of:

a. integrating the backbone ( 60 ) within the walls ( 56 A, 56 B, 56 C, 56 D) of the multi-plane pressure plate ( 42 ) coupled to the current collector ( 40 ) secured adjacent the end cell ( 36 ) of the fuel cell stack ( 30 ) to form a low thermal mass integrated end plate assembly ( 38 ) that prohibits lateral motion of the backbone ( 60 ) in any direction;

b. deflecting tie rod ends ( 62 , 64 , 66 , 68 ) of the backbone ( 60 ) within the gap ( 84 ) adjacent the deflection plane ( 50 ) of the multi-plane pressure plate ( 42 );

c. extending the beam ( 82 ) of the backbone ( 60 ) between opposed exterior perimeters ( 48 ) of the multi-plane pressure plate ( 42 );

d. redistributing a clamping load from the tie-rod ends ( 62 , 64 , 66 , 68 ) of the backbone ( 60 ) through the center ( 46 ) of the multi-plane pressure plate ( 42 ); and,

e. providing a load follow-up load wherein the tie-red ends ( 62 , 64 , 66 , 68 ) deflect within the gap ( 84 ) to a predetermined value in an absence of contacting the deflection plane ( 50 ).

7. The method of claim 6 , further comprising deflecting the tie rod ends ( 62 , 64 , 66 , 68 ) into the gap ( 84 ) responsive to varying fuel cell temperatures, and permitting expansion of the fuel cell stack ( 30 ) within operating dynamic limits of the fuel cell stack ( 30 ).

8. The method of claim 6 , comprising the further step of configuring the backbone ( 60 ) with a predetermined flexural strength to prohibit expansion of the fuel cell stack ( 30 ) beyond operating dynamic limits of the fuel cell stack ( 30 ).

9. The method of claim 6 , comprising the further steps of gradually decreasing deflection of the tie rod ends ( 62 , 64 , 66 , 68 ) of the backbone ( 60 ) responsive to thinning of the fuel cells ( 32 ) resulting from compressive creep, and maintaining the follow-up load responsive to the decreasing deflection of the tie rod ends ( 62 , 64 , 66 , 68 ).