In the drawings:
Similar or functionally equivalent elements are designated by the same reference symbols in each of the Figures.
A fuel cell stack bearing the general reference 100 which is illustrated in
Each of the fuel cell units 102 comprises a (not illustrated in detail) housing which, for example, may be assembled from a first sheet metal shaped part in the form of an upper housing part and a second sheet metal shaped part in the form of a lower housing part such as is described and illustrated in DE 100 44 703 A1 for example.
Each of the fuel cell units 102 is provided with passage openings for a fuel gas and with passage openings for an oxidizing agent, wherein the passage openings of the successive fuel cell units 102 in the direction of the stack 104 are aligned with one another in such a manner that supply channels for the fuel gas and for the oxidizing agent as well as exhaust channels for surplus fuel gas and surplus oxidizing agent are formed through the fuel cell stack 100.
A substrate having a cathode electrolyte anode unit (CEA unit) arranged thereon is held on the housing of each fuel cell unit 102, whereby the electro-chemical fuel cell reaction takes place in the CEA unit.
The CEA units of neighbouring fuel cell units 102 are connected to one another by electrically conductive contact elements.
The housings of successive fuel cell units 102 are connected to one another by means of electrically insulating, gas-tight seal elements.
The upper end face of the fuel cell stack 100 is bounded by a first stack end element 106 in the form of an upper end plate 108.
The lower end face of the fuel cell stack 100 is bounded by a second stack end element 110 in the form of a lower end plate 112.
The end plates 108, 112 have a larger horizontal cross section than the fuel cell units 102 and project laterally beyond the stacked fuel cell units 102.
The end plates 108, 112 are preferably made of a metallic material which is chemically and mechanically stable at the operating temperature of the fuel cell units 102 and they may comprise gas passage channels that are connected to the supply channels and exhaust channels for the fuel gas and the oxidizing agent which extend through the fuel cell units 102.
Furthermore, in order to apply the requisite sealing forces to the seal elements of the fuel cell units 102 and the requisite contact forces to the contact elements of the fuel cell units 102 during operation of the fuel cell stack 100, the fuel cell stack 100 comprises a tensioning device 114 by means of which the stack end elements 106, 110 and thus the fuel cell units 102 arranged therebetween are braced against each other.
In the case of the embodiment of a fuel cell stack 100 illustrated in
In order to enable this hooking process to be effected, the end regions 120a, 120b of the tensioning tapes 118 are provided with a respective, rectangular for example, hooking opening 122, whilst the side walls 124 of the lower end plate 112 are provided with a plurality of hooking noses 126 which comprise a downwardly protruding projection 128.
When hooking the tensioning tapes 118 on the fuel cell stack 100, the end regions 120a, 120b of the tensioning tapes are pulled down to such an extent that the projections 128 of the hooking noses 126 of the lower end plate 112 can be moved through the hooking openings 122 in the tensioning tapes 118 and the lower edges of the hooking openings 122 then come to rest behind the respective projections 128 forming an under-cut after they have been pulled upwardly again due to the self-elasticity of the respective tensioning tape 118 and in consequence they are prevented from being detached from the lower end plate 112 by the projections 128.
The connection between a tensioning tape 118 and the lower end plate 112 can be released in a simple manner in that the end region 120a, 120b of the tensioning tape 118 is pulled downwardly until the respective hooking opening 122 is aligned with the hooking nose 126 in such a way that the edge of the hooking opening 122 can be moved away from the side wall 124 of the lower end plate 112 past the hooking nose 126 so as to disengage the tensioning tape 118 from the hooking nose 126.
The two tensioning tapes 118 are spaced from each other in a horizontal transverse direction 119 running perpendicularly to the direction of the stack 104.
The tensioning tapes 118 are preferably formed from a metallic material, in particular, from a material consisting of a steel sheet.
As an alternative thereto, other materials having a sufficiently high tensile strength and thermal stability could also be used, such as suitable synthetic materials for example.
If the temperature of the fuel cell stack 100 changes and in particular is brought up to the operating temperature, the fuel cell units 102 together with the stack end elements 106 and 110 on the one hand and the tensioning elements 116 on the other may expand in the direction of the stack 104 by different amounts due to their different average coefficients of thermal expansion. In order to be able to compensate for such different longitudinal expansions but nevertheless produce a sufficiently high contacting force and sealing force between the fuel cell units 102 by means of the tensioning device 114, each of the tensioning elements 116 comprises two resilient longitudinal expansion compensating elements 130 which are integrated into the two sections 134a, 134b of the respective tensioning tape 118 running in parallel with the direction of the stack 104 in the form of concertina-like folded or corrugated regions 132.
If the fuel cell units 102 expand in the direction of the stack 104 to a greater extent than the material of the tensioning tapes 118, then the expansion of the folded or corrugated regions 132 in the direction of the stack 104 increases by an amount corresponding to the difference in the longitudinal expansion in that the apex lines 136 of the folded or corrugated region 132 move further apart.
Conversely, shortening of the folded or corrugated region 132 in the direction of the stack 104 is obtained by virtue of the apex lines 136 of the folded or corrugated region 132 being moved closer together.
In consequence, a difference in the thermal expansion of the fuel cell units 102 on the one hand and the material of the tensioning elements 116 on the other can be balanced out, overstretching of the tensioning elements 116 can be prevented and a desired tensioning force effective on the fuel cell units 102 can be maintained by a reversible variation in the length of the longitudinal expansion compensating elements 130.
The section 138 of each tensioning tape 118 that is arranged between the sections 134a, 134b which run parallel to the direction of the stack 104 and rest in flat manner against the side walls 124 of the upper end plate 108 is itself disposed in flat manner on the upper surface of the upper end plate 108 so that the tensional force of the tensioning elements 116 is then evenly distributed and effective over a large surface area of the upper end plate 108, this thereby ensuring a uniform flow of force through the upper end plate 108 to the fuel cell units 102
A second embodiment of a fuel cell stack 100 that is illustrated in
For the purposes of seating these pressure transmission elements 138, the upper end plate 108 of the fuel cell stack 100 is provided on the lower surface thereof with a substantially cuboidal recess 140.
The resilient pressure transmission elements 138 may, in particular, be in the form of metal sheets which are each provided with a full corrugation 141 and are arranged on one another in pairs in such a manner that the crests 142 of the full corrugations 141 face one another and the feet 144 thereof are supported on the upper end plate 108 or on the uppermost fuel cell unit 102.
By using such additional resilient pressure transmission elements 138, the flow of force between the fuel cell units 102 on the one hand and the tensioning elements 116 and the stack end element 106 on the other can be controlled in an even more precise and equalised manner.
In all other respects, the second embodiment of a fuel cell stack 100 that is illustrated in
A third embodiment of a fuel cell stack 100 that is illustrated in
The thermal insulation 146 is capable of transmitting forces from the tensioning elements 116 to the fuel cell units 102.
Furthermore, the thermal insulation 146 enables the fuel cell units 102 to be operated at an operating temperature which is significantly above the ambient temperature.
The third embodiment of a fuel cell stack 100 that is illustrated in
Such high temperature fuel cell units may, in particular, be of the SOFC (Solid Oxide Fuel Cell) type.
In all other respects, the third embodiment of a fuel cell stack 100 that is illustrated in
A fourth embodiment of a fuel cell stack 100 which is illustrated in
In particular, the connection of the two end regions 120a, 120b to one another may, as is illustrated in
Subsequently, the first section 152 and the second section 154 are deformed by a stamping process in such a way that the width B thereof, i.e. their elongation in the direction of the stack 104, exceeds the width b of the passage opening 156 in the second end region 120b, i.e. the elongation thereof in the direction of the stack 104, so that the first section 152 that has been pushed through the passage opening 156 can no longer be moved back through the passage opening 156 into the plane of the first end region 120a.
By fixing the two end regions 120a and 120b of each tensioning tape 118 together, the desired tensional force is produced in the tensioning tapes 118, this force being transmitted via the end plates 108, 112 to the fuel cell units 102 in order to subject them to the desired sealing forces and contact forces.
The sections 138a and 138b of each tensioning tape 118 that are arranged between the sections 134a, 134b running parallel to the direction of the stack 104 lie in flat manner on the outer surface of the upper end plate 108 or the lower end plate 112 remote from the fuel cell units 102 so as to ensure that force is applied uniformly over a large surface area to the end plates 108, 112 by the tensioning tapes 118.
The length compensating elements 130 envisaged in the first embodiment can be dispensed with in the fourth embodiment of a fuel cell stack 100 illustrated in
In all other respects, the fourth embodiment of a fuel cell stack 100 that is illustrated in
A fifth embodiment of a fuel cell stack 100 which is illustrated in
As can be seen from
The lower edges of the lateral sections 164a, 164b of the tensioning strip 158 merge along a bending line 166 into a respective end region 168a, 168b of the upper tensioning strip 158a which is aligned transversely to the direction of the stack 104.
A lower tensioning strip 158b extends around the lower end plate 112 whilst a middle section 170 thereof lies in flat manner on the outer surface 172 remote from the fuel cell units 102 and the two lateral sections 174a, 174b lie in flat manner on the side walls 124 of the lower end plate 112.
The upper edges of the lateral sections 174a, 174b merge along a bending line 176 into a respective end region 178a and 178b of the lower tensioning strip 158b which is aligned transversely to the direction of the stack 104. The end regions 168a, 168b of the upper tensioning strip 158a and the end regions 178a, 178b of the lower tensioning strip 158b are fixed together by means of a respective fixing device 180 which comprises a fixing strip 182 running in the transverse direction 119 and a seating strip 184 running parallel to the fixing strip 182 and also several, two for example, fixing screw members 186 which are mutually spaced in the transverse direction 119.
The upper surface of the fixing strip 182 rests from below on the respectively associated end region 178a, 178b of the lower tensioning strip 158b, and the lower surface of the seating strip 184 rests from above on the respectively associated end region 168a, 168b of the upper tensioning strip 158a.
The fixing screw members 186 extend through passage openings in the seating strip 184 and the respective end regions 168a, 178a and 168b, 178b and are screwed into threaded blind holes which are provided in the fixing strip 182.
Between the head 188 of each fixing screw member 186 and the respectively associated seating strip 184, there is arranged a respective spring element 190 in the form of a compression spring which is supported on the head 188 and on the seating strip 184 and biases the seating strip 184 downwardly against the respectively associated end regions 168a and 168b.
In the state of the fuel cell stack 100 illustrated in
If, in the event of a change of temperature, the fuel cell units 102 together with the stack end elements 106 and 110 expand in the direction of the stack 104 to a greater extent than the tensioning strips 158, then the seating strips 184 of the fixing devices 180 are moved away from the fixing strips 182 in the direction of the stack 104 against the restoring force of the spring elements 190 so that the end regions 168a and 178a and also 168b and 178b are then spaced from one another by the distance d as is illustrated in
The spring elements 190 of the fixing devices 180 are thus effective as longitudinal expansion compensating elements which compensate for a difference d between the thermal expansions of the fuel cell units 102 and the stack end elements 106, 110 on the one hand and the tensioning strip 158 on the other.
In all other respects, the fifth embodiment of a fuel cell stack 100 that is illustrated in
A sixth embodiment of a fuel cell stack 100 which is illustrated in
The longitudinal expansion compensating elements 130 on the tensioning tapes 118 that were envisaged in the first embodiment can be dispensed with in this embodiment, but they may be provided however in a variant of this embodiment.
In all other respects, the embodiment of a fuel cell stack 100 that is illustrated in
A seventh embodiment of a fuel cell stack 100 that is illustrated in
Hereby, the deformable recesses 192 may have a substantially rhombic shape for example.
The regions 194 of the tensioning tapes 118 are greater in width than the sections of the tensioning tapes 118 located outside these regions.
The regions 194 each comprise two webs 196 which bound the respective recess and they may, for example, be of approximately the same width as the sections of the tensioning tapes 118 located outside the regions 194.
In the starting state illustrated in
If, in the event of a change in temperature, the fuel cell units 102 together with the stack end elements 106 and 110 expand in the direction of the stack 104 to a greater extent than the material of the tensioning tapes 118, then the deformable recess 192 is stretched in the direction of the stack 104 to produce a larger elongation L, and the expansion of the region 194 in the direction of the stack 104 increases accordingly.
It is thus possible to compensate in this way for the different thermal expansions of the fuel cell units 102 and the stack end elements 106, 110 on the one hand and the material of the tensioning tapes 118 on the other.
When the temperature reverts to the starting temperature, the region 194 together with the deformable recess 192 deform back from the state illustrated in
In all other respects, the seventh embodiment of a fuel cell stack 100 that is illustrated in
Number | Date | Country | Kind |
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10 2006 028 439.9 | Jun 2006 | DE | national |