Abstract:
For operation, PEMFCs require among other things a compressor for the cathode air, and a system for removing the water which is generated on the cathode side as a result of the electrochemical reaction. According to an embodiment of the present invention the removal of water is supported in that the fuel cell is made to rotate by way of an electric motor so that the water contained in the cathodes of the fuel cell can be extracted by centrifugal force. To this effect the air channels on the cathode side are arranged so as to extend radially or in a spiral shape from the inside towards the outside. In this way the efficiency of the fuel cell can be significantly improved.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of the filing date of U.S. Provisional Patent Application No. 60/609,969 filed Sep. 15, 2004, the disclosure of which is hereby incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     Fuel cells, in particular so-called proton exchange membrane fuel cells (PEMFCs) require for operation, among other things, a compressor for the cathode air, and a system for letting off the water generated on the cathode side by electrochemical reaction. In order to prevent oversaturation by the generated water on the cathode side, which oversaturation would be disadvantageous for implementation, and in this way achieve an effective water production rate, the water must be continuously removed in the form of water vapour and water droplets. Often the air stream generated by the compressor is insufficient for optimal removal of the water generated on the cathode side. 
     There may be a need to provide an improved fuel cell system for generating electrical energy, mechanical energy or water. 
     SUMMARY OF THE INVENTION 
     The present invention relates to fuel cell systems. In particular, the present invention relates to a fuel cell system for generating electrical energy, mechanical energy and water; to the use of such a fuel cell system in an aircraft; and to an aircraft comprising such a fuel cell system. 
     According to an exemplary embodiment of the present invention, as stated in claim  1 , the above object may be met by means of a fuel cell system for generating electrical energy, mechanical energy and water. The fuel cell system comprising a fuel cell held so as to be rotatable, a motor and a first non-positive connection between the fuel cell and the motor, wherein by way of the first non-positive connection energy is transferable from the motor to the fuel cell so that the fuel cell can be made to rotate. 
     As a result of the design of the fuel cell system the fuel cell may be made to rotate in such a way that an additional conveying force is provided, which may promote removal of the water generated by the electrochemical reaction within the fuel cell. This force may be derived from a centrifugal force in that the fuel cell held so as to be rotatable is made to rotate. In this way the removal of water may be significantly accelerated, which can lead to a more effective cathode reaction and thus to an increase in the efficiency of the fuel cell. 
     According to a further exemplary embodiment of the present invention, as stated in claim  2 , the fuel cell system further comprises a compressor, wherein the compressor is designed to provide cathode air to the fuel cell, and wherein as a result of the rotation of the fuel cell the water generated in an electrochemical reaction in the fuel cell on a cathode side of the fuel cell is extractable by centrifugal force. 
     Thus, a fuel cell system may be provided in which removal of the water generated on the cathode side takes place not only by means of the centrifugal force which may result from the rotation of the fuel cell system or of the fuel cell, but also by means of compressed air which may be generated by the compressor and which is fed into the cathode of the fuel cell. The addition of centrifugal force and conveying force (resulting from the air stream generated by the compressor) may accelerate water removal from the cathode space and thus causes an effective cathode reaction. 
     According to a further exemplary embodiment of the present invention, as stated in claim  3 , the first non-positive connection between the fuel cell and the motor comprises a first clutch and a torque converter, wherein the first clutch is a mechanical or electromechanical clutch. 
     Thus, the power may be transmitted in a metered way from the motor to the fuel cell. For example, if necessary, decoupling the fuel cell from the motor may also be possible so that for example the motor can drive other components without driving the fuel cell. 
     According to a further exemplary embodiment of the present invention, as stated in claim  4 , the fuel cell system further comprises a load controller, wherein the load controller is designed to distribute the required electrical energy between the motor and further electrical consumers, or is designed to control or regulate the torque converter and the clutch. The electrical energy required for this may be internally supplied by the fuel cell or by an external energy source. 
     It may be thus possible to ensure electronic energy management which may provide energy to the motor or to other electrical consumers as required. Furthermore, the load controller may control or regulate the torque converter and the clutch of the non-positive connection between the fuel cell and the motor so that in this way electronic speed control of the fuel cell may be ensured. 
     According to a further exemplary embodiment of the present invention, as stated in claim  5 , the rotary speed of the fuel cell and thus a water discharge from cathode-side air channels of the fuel cell can be regulated or controlled, either continuously or intermittently, by way of the load controller and the torque converter, depending on the electrical or mechanical load. 
     Thus, it may for example be possible, in the case of an increased mechanical load on the motor, to regulate the rotary speed of the fuel cell down so that the energy requirement of the motor may drop accordingly. 
     According to a further exemplary embodiment of the present invention, as stated in claim  6 , a rotary speed of the compressor can be regulated or controlled, either permanently or intermittently, by way of the load controller and the torque converter, depending on the electrical or mechanical load, wherein a rotary speed of the fuel cell can be regulated or controlled, either permanently or intermittently, by way of the load controller and the torque converter, independently of the electrical or mechanical load. 
     In this way the rotary speed of the compressor and the fuel cell may be set independently of each other, wherein the rotary speed of the compressor may be guided by the electrical or mechanical load, and wherein the rotary speed of the fuel cell may be set or regulated independently thereof. 
     According to a further exemplary embodiment of the present invention, as stated in claim  7 , the fuel cell system further comprises a water pump and a second non-positive connection between the motor and the water pump, wherein, by way of the second non-positive connection, energy from the motor can be transmitted to the water pump so that the water pump can be made to rotate, and wherein the water pump returns a condensate from the cathode exhaust air of the fuel cell for further utilisation by the fuel cell, or removes said condensate from the fuel cell system. 
     Thus, a fuel cell system may be stated which can independently return the cathode air removed by centrifugal force, or, if applicable, may return said cathode air to the fuel cell for further utilisation within the fuel cell. 
     According to a further exemplary embodiment of the present invention, as stated in claim  8 , the fuel cell system further comprises a shaft which is non-positively connected to an armature of the motor or to a displacement device of the compressor. 
     According to a further exemplary embodiment of the present invention, as stated in claim  9 , the fuel cell is constructed from rotation-symmetrical components as a hollow cylinder. 
     This may ensure smoothness of running and low mechanical load for example of the shaft during rotation of the fuel cell on its longitudinal axis. 
     According to a further exemplary embodiment of the present invention, as stated in claim  10 , in the region of the fuel cell the shaft is a first hollow shaft, wherein the first hollow shaft is designed to feed hydrogen to an anode of the fuel cell. 
     Thus, even with rotation of the fuel cell on the rotary axis, hydrogen may be fed to the fuel cell anode in an easy manner. 
     According to a further exemplary embodiment of the present invention, as stated in claim  11 , a second hollow shaft is provided which encloses the first hollow shaft, wherein the second hollow shaft is designed for feeding air to the fuel cell. 
     It may thus be possible to feed different gases independently of each other to the fuel cell. 
     According to a further exemplary embodiment of the present invention, as stated in claim  12 , the fuel cell comprises air channels on the cathode side, and gas channels on the anode side, wherein the air channels are arranged so as to extend radially or in a spiral shape from the inside towards the outside, and wherein the arrangement of the gas channels corresponds to the arrangement of the air channels. 
     Thus, the removal of water from the cathode space may thus be further enhanced. 
     According to a further exemplary embodiment of the present invention, as stated in claim  13 , the fuel cell comprises a collection space for water, and a housing which encloses the collection space, wherein the housing accommodates bearing elements for the shafts and also accommodates rotary transmission leadthroughs. 
     It may thus be possible to collect within the fuel cell the water removed from the cathode. 
     Further objects, embodiments and advantages of the invention are disclosed in the dependent claims and in the further independent claims. 
     Below, the invention is described in more detail by means of exemplary embodiments with reference to the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a diagrammatic view of a fuel cell system according to an embodiment of the present invention. 
         FIG. 2  shows a diagrammatic view of a further fuel cell system according to another embodiment of the present invention. 
         FIG. 3  shows a diagrammatic cross-sectional view of a bipolar plate according to an embodiment of the present invention. 
         FIG. 4  show a diagrammatic section view of a fuel cell system according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description of the figures the same reference signs are used for identical or similar elements. 
       FIG. 1  shows a first diagrammatic view of a fuel cell system according to an embodiment of the present invention. As shown in  FIG. 1 , the fuel cell system comprises a proton exchange membrane fuel cell (PEMFC)  1 , an electric motor  12 , a compressor  11 , a clutch  10 , a torque converter  9  and a pump  14 . 
     By way of a corresponding line, hydrogen  17  is fed to the fuel cell  1 , and by way of a corresponding other line, humid air  19  is removed from the fuel cell  1 . In this arrangement, the feeding in of hydrogen  17  is by way of a hollow shaft (not shown in  FIG. 1 ) which forms part of a main shaft  4 . The hydrogen is then fed to an anode (not shown in  FIG. 1 ) of the fuel cell  1  so that an electrochemical reaction within the fuel cell can take place, by way of which reaction electrical energy and water are generated. 
     The water that arises in the cathode of the fuel cell  1 , is removed from the cathode and is removed as humid air  19  or as water. 
     In this arrangement the fuel cell  1  is held, so as to be rotatable, on the shaft  4  and by way of the clutch  10  and the torque converter  9  is non-positively connected to the electric motor  12 . Furthermore, the fuel cell  1  can be made to rotate by means of the electric motor  12 . According to the invention, this rotary movement leads to improved removal of the water from the cathode system of the fuel cell  1 , which improved removal is due to the centrifugal force generated, and thus leads to improved efficiency of the fuel cell. 
     As shown in  FIG. 1 , the fuel cell system further comprises a pump  14  which, by way of a second non-positive connection that is consists of and/or comprises a second clutch  15  and a second torque converter  16 , is connected to the shaft  4 , and is thus drivable by way of the electric motor  12 . The water pump  14  can for example be used to return a condensate from the cathode exhaust air  19  to the fuel cell  1  so that it can continue to be used within the fuel cell. Of course, the pump  14  can also be used to entirely remove the condensate from the humid air  19  from the fuel cell system. Subsequently, the condensate can for example be fed to the water supply system of an aircraft in which the fuel cell system is installed. 
     The electric motor  12  comprises an armature (not shown in  FIG. 1 ), while the compressor  11  comprises a displacement device (not shown in  FIG. 1 ). Both the displacement device and the armature are non-positively connected to the shaft  4 . 
     In order to minimise the mechanical load on the rotating parts, the fuel cell  1  is constructed from rotationally symmetrical components as a hollow cylinder. 
     Furthermore, the fuel cell  1  comprises air channels on the cathode side, and gas channels on the anode side, which channels are arranged radially or in a spiral shape from the inside towards the outside. In this way the efficiency of the fuel cell can be further enhanced. 
       FIG. 2  shows a second diagrammatic view of a fuel cell system according to another embodiment of the present invention. In this arrangement the fuel cell  1  is designed such that hydrogen gas  17  can be fed to it by way of a first hollow shaft (see  FIG. 4 ), and such that air  18  can be fed to it by way of a second hollow shaft (see  FIG. 4 ). 
     No compressor is provided in the fuel cell system shown in  FIG. 2 . 
     A mechanical or electromechanical clutch  10  and a torque converter or gear arrangement  9  is arranged between the electric motor  12  and the fuel cell  1 . 
       FIG. 3  shows a diagrammatic cross-sectional view of a bipolar plate according to an embodiment of the present invention. As shown in  FIG. 3 , the bipolar plate  2  comprises cathode air channels  21 . Furthermore, in radial direction the bipolar plate  2  is designed in the manner of cooling lamellae or blades. The cooling lamellae or blades  22  can be used for cooling the fuel cell. The fuel cell, together with the bipolar plates  2 , is held in its housing so as to be rotatable (see  FIG. 4 ). In this arrangement the housing comprises an inflow channel and an outflow channel for cooling air. The bipolar plates are held, so as to be rotatable, in the region of the central borehole  3 . 
     According to one embodiment of the present invention the housing is an axial blower. 
       FIG. 4  shows a diagrammatic section view of a fuel cell system according to an embodiment of the present invention. The PEMFC  1  is made from rotationally symmetrical components as a hollow cylinder. In the central borehole  3  (see  FIG. 3 ) of the bipolar plates  2  there is a through shaft  4  which is rigidly connected to the displacement device  111 , which is for example a piston or a rotary slide valve, of the compressor  11  and to the armature  121  of the electric motor  12 . Of course, according to another embodiment of the present invention the compressor  11  can also be done without. 
     In the region of the fuel cell  1  the shaft  4  is a hollow shaft  5 . By way of this hollow shaft  5 , hydrogen  17  flows to the anode of the fuel cell  1 . A further hollow shaft  6  encompasses the hollow shaft  5  for the air supply. By way of rotary transmission leadthroughs, the hydrogen  17  is supplied on the free side of the fuel cell  1 . If there is no compressor  11 , the air too is supplied by way of the rotary transmission leadthroughs on the free side of the fuel cell  1 . 
     When the fuel cell  1  rotates on the shaft  4 , the water generated on the cathode side during the electrochemical reaction is extracted by centrifugal force into the collection space  7 . To this effect the cathode-side air channels  21  in the bipolar plate  2  are radially aligned (see  FIG. 3 ). The collection space  7  is enclosed by a housing  8  which accommodates the bearing elements of the shafts ( 4 ,  5 ,  6 ) and further accommodates the rotary transmission leadthroughs. The rotary axle  4  and the hollow shafts  5 ,  6  of the fuel cell or of the fuel cell system are held in the housing  8  so that in the space enclosing the fuel cell  1  the cathode water can be collected and removed by way of an aperture  81 . However, it is also possible for the rotary axle  4  and the hollow shafts  5 ,  6  of the fuel cell  1  not to be held in a housing  8  so that the cathode water can be removed into the free space enclosing the fuel cell  1 . 
     The drive for rotation of the fuel cell  1  is provided by the electric motor  12 , which is non-positively connected to the shaft  4 . A mechanical or electromagnetic clutch and a torque converter (gear arrangement) can be arranged between the electric motor  12  and the fuel cell  1 . 
     The end plate  41  of the fuel cell  1  can comprise gas channels. 
     Within the hollow shafts  5 ,  6  and the compressor  11  there is an air space  45  which can accommodate corresponding gases. 
     The clutch  10  and the torque converter  9  (shown in  FIG. 1 ) are constructed in such a way that, with the clutch disengaged too, the air stream can flow from the compressor  11  to the fuel cell  1  by way of the hollow shaft  6 . The electrical energy required by the electric motor  12  is supplied by the fuel cell  1 . 
     The electric motor  12  comprises a ventilator  46 , an exciting winding  47 , a stator  48  and a commutator  49 . 
     By way of the clutch  15 , mechanical energy can be transmitted to further (mechanical) consumers such as for example to a pump. 
     By way of the electrical load controller  13 , distribution of the electrical energy required is regulated between the electric motor  12  (by way of lines  44 ) and the external electrical consumers, and furthermore the switch state of the torque converter  9  of the clutch (see  FIG. 1 ) is regulated. By way of the load controller  13 , external electrical energy can also be supplied to the electric motor  12  for other operating states, e.g. for starting up the system. The external electrical energy is fed to the load controller  13  by way of supply lines  131 . The internal electrical energy (generated by the fuel cell  1 ) is fed to the load controller  13  by way of current collectors  42  and lines  43 . The electrical energy for further electrical consumers is discharged from the load controller by way of lines  132 . 
     The water arising in the collection space  7  and the humid air from the cathode channels  21  are let out by way of an aperture  81  in the housing  8 , for example by way of a condenser with condensate separator, or by way of a humidity-heat exchanger (not shown in  FIG. 4 ) for further utilisation in the process. 
     Cooling of the PEMFC  1  takes place by way of the bipolar plates or cooling plates of the fuel cell  1 , which are enlarged in radial direction to the extent that the projecting rings are cooling lamellae or blades  22  (see  FIG. 3 ). 
     The fuel cell system according to the invention can for example be used within an aircraft. 
     Implementation of the invention is not limited to the preferred embodiments shown in the figures. Instead, a multitude of variants are imaginable which use the solution shown and the principle according to the invention even in the case of fundamentally different embodiments. 
     In addition it should be pointed out that “comprising” does not exclude other elements or steps, and “a” or “one” does not exclude a plural number. Furthermore, it should be pointed out that features or steps which have been described with reference to one of the above embodiments can also be used in combination with other features or steps of other embodiments described above. Reference signs in the claims are not to be interpreted as limitations.