Abstract:
A cooling fan system for a vehicle with fuel cell propulsion, wherein air is moved by means of a cooling fan for cooling purposes through a heat exchanger and can thereafter be supplied to the environmental air either directly or indirectly after satisfying one or more further cooling tasks, characterized in that an air branching device is provided which supplies at least a part of the air delivered by each fan to a duct and thereby enables the use of the branched-off air for the starting of the fuel cells and/or for the maintenance of the operation of the fuel cells.

Description:
TECHNICAL FIELD  
         [0001]    The present invention relates to a cooling fan system for a vehicle with fuel cell propulsion, wherein air is moved by means of a cooling fan for cooling purposes through a heat exchanger and can thereafter be supplied to the environmental air either directly or indirectly after satisfying one or more further cooling tasks. The invention relates furthermore to a method for the operation of a fuel cell system.  
         BACKGROUND OF THE INVENTION  
         [0002]    Many proposals have already been made for the equipping of vehicles with fuel cell propulsion systems. Such vehicles are already being constructed and tested.  
           [0003]    With such fuel cell propulsion systems, the fuel cells deliver electrical energy which, after appropriate processing, is applied to one or more drive motors which take care of the propulsion of the motor vehicle.  
           [0004]    For fuel cell propulsion systems for vehicles, PEM (Proton Exchange Membrane) fuel cells are currently preferred which are connected in parallel and/or in series to one another and form a so-called stack. The fuel cells are supplied, on the one hand, with hydrogen from a suitable source. Protons which originate from the hydrogen and pass through the membranes of the fuel cells combine in the fuel cells with the oxygen of the air which is supplied to form water with the simultaneous generation of electrical energy.  
           [0005]    The vehicle can be equipped with a hydrogen storage tank, and may, however, also be fed with a synthesized hydrogen-rich gas which is obtained from a hydrocarbon such as methanol. In this case, the hydrocarbon is processed in a processing device in the form of a so-called reformer to form the synthesized hydrogen-rich gas. When a reformer is used, it also requires air.  
           [0006]    Fuel cells are also known which are directly fed with methanol, with the methanol consisting of up to 97% water. Such fuel cell systems require oxygen for the power generating reaction and must be supplied with air by a compressor.  
           [0007]    Independently of the type of fuel cells which are used, a compressor is always required which makes available the compressed air for the fuel cells or for the reformer. Part of the output power of the fuel cell system is also applied to an electric motor which is required in operation to drive the compressor.  
           [0008]    In practice, problems arise with the starting of a fuel cell system.  
           [0009]    One known solution involves the use of a traction battery with, for example, 288 V operating potential. This traction battery has in principle three different tasks:  
           [0010]    On the one hand, it is used to drive the main compressor in order to feed air compressed by this compressor into the fuel cell system, so that power is generated which then replaces the traction battery as the power source for the electric motor driving the compressor.  
           [0011]    The second task of the traction battery is to assist dynamically the electric motor or electric motors which propel the vehicle so that, for example, with fast acceleration or at elevated speeds, the power of the traction battery supplements the electrical output power of the fuel cell system.  
           [0012]    The third task lies in the fact that a traction battery can be used in order to realize regenerative braking for example. That is to say, on braking of the vehicle, the kinetic energy which is present is partly converted into electrical energy which can then be stored in the traction battery.  
           [0013]    Although a traction battery can be useful for these different purposes, it represents an expensive and heavy component, so that one would be pleased to dispense with it. If, however, the traction battery is dispensed with, it could no longer be used to start up the fuel cell system.  
           [0014]    For the starting of the fuel cell system, air is required. The air compressor is normally driven from the fuel cell potential; however, this is not yet available. In the absence of a traction battery, it has already been proposed to supply the fuel cell system with sufficient air by means of a 12 V auxiliary fan, i.e., a so-called start-up blower, so that the power generation starts there and the system can be gradually run up until the power generation by the fuel cell system is sufficient in order to maintain the system in operation.  
           [0015]    Irrespective of whether one operates with a traction battery or with an auxiliary blower, many components which make the system more complicated or more expensive, such as fans, radiators, pipes, 288 V batteries, etc., are necessary which one would prefer to do without.  
         SUMMARY OF THE INVENTION  
         [0016]    The object of the present invention is to make sufficient air available so that the fuel cell system can be started and run up without using a traction battery or an auxiliary fan.  
           [0017]    In order to satisfy this object, provision is made, in accordance with the invention, for an air branching device to be provided which supplies at least a part of the air delivered by each fan to a duct and thereby enables the use of the branched-off air for the starting of the fuel cells and/or for the maintenance of the operation of the fuel cells.  
           [0018]    In other words, it has been recognized, in accordance with the invention, when using a fuel cell propulsion system in which a cooling fan driven by the normal onboard battery is used for the cooling of liquid flowing through a heat exchanger, with the throughflowing air also being capable of being used for further cooling tasks, that the system consisting of the cooling fan and heat exchanger is unnecessary per se during the starting of the fuel cell system, since the heat which then arises is restricted, and that the cooling fan associated with the heat exchanger can thus be exploited for the starting of the fuel cell system until the fuel cell system delivers sufficient power to drive the compressor itself. That is to say, the cooling fan is used in the short term for the starting of the fuel cell system.  
           [0019]    This can in principle take place in such a way that an air branching device, which is simply formed by a fixed guide wall, is provided and always branches off a part of the air flow produced by the cooling fan and supplies it via a suitable line to the fuel cells and/or to a reformer. On operation of the system, a device must then be provided in order to close off the duct when the compressor starts to run in order to prevent the compressed air generated by the compressor from escaping through the corresponding duct in the form of a reverse flow. This need could indeed be avoided if the branched-off air flow generated by the cooling fan is supplied to the inlet of the compressor and thus via the compressor to the fuel cells and/or the reformer.  
           [0020]    A further possibility is to make the air branching device movable so that it can be switched between a first substantially inactive position and a second position which brings about the branching off of the air. In this manner it is not only possible to use part of the air flow delivered by the cooling fan, but rather the entire air flow can be used for the starting of the fuel cell system.  
           [0021]    The cooling fan can in principle be a suction fan which is arranged downstream of the heat exchanger and sucks the air through the latter, with the air branching device then being arranged downstream of the suction fan. Such suction fans are customary with fuel cell propulsion systems.  
           [0022]    It is, however, more favorable if each cooling fan is a pusher fan which is arranged in front of the heat exchanger. A fan of this kind is better able to deliver the airflow required for the starting of the fuel cells because it operates more efficiently under backpressure conditions.  
           [0023]    When using a pusher fan, it is preferably connected to the heat exchanger by means of a housing which avoids air losses.  
           [0024]    It is particularly favorable when an air guiding housing is arranged downstream of the heat exchanger directly adjacent to the latter so that all the air flowing through the heat exchanger enters into the air guiding housing.  
           [0025]    Various possibilities exist in accordance with the invention in order to realize the air branching device. This can, in particular, be realized by adjustable plates, which, in a first position, permit the air moving through the heat exchanger to pass and, in a second position, close against one another in order to supply the air to the duct leading to the fuel cells. The plates are preferably arranged at the downstream side of the air guiding housing.  
           [0026]    They can, for example, be arranged in the manner of a louver window. Another possibility is to arrange them in the manner of an iris diaphragm, with the plates forming a central opening in the state closed against one another, which lies opposite to the entry to the duct leading to the fuel cells.  
           [0027]    The possibility also exists of arranging the plates in the manner of a roller shutter.  
           [0028]    It is particularly favorable when an air collecting box extends over a region of the air guiding housing which is not covered over by the air branching device in the air branching-off position and collects the air deflected by the air branching device and directs it to the duct leading to the fuel cells. An air collecting box of this kind can be straightforwardly used with an air branching device consisting of plates, in particular if these are arranged in the manner of a louver window (Venetian blind) or in the manner of a roller shutter, since the air collecting box extends over the entire width of the heat exchanger and the plates can close against an edge region of the air collecting box.  
           [0029]    A further possibility for realizing the air branching device and to use it with an air collecting box is to form the air branching device as a roller blind.  
           [0030]    Instead of using an air collecting box, the air branching device can in the second position fully close off the air outlet side of the air guiding housing and the latter can have a connection for a duct leading to the fuel cells. In this way, the need to use a separate air collecting box is avoided, i.e., the air guiding housing, which is in any event present, is itself used as the air collecting box.  
           [0031]    With embodiments utilizing an adjustable air branching device, the positioning motor for the positioning of the same is preferably mounted on the air guiding housing.  
           [0032]    An air filter can be built into the air collecting box or into the duct leading to the fuel cells in order to ensure that the fuel cells and/or the reformer are only fed with clean air.  
           [0033]    It is particularly favorable that in the invention the cooling system consisting of the cooling fan and the heat exchanger with the air branching device and the housings associated therewith, as well as any motor for the positioning of the air branching device, can be built up as a module, since it can then be designed in a space-saving manner as a unit which is easily exchangeable and which can be manufactured at favorable cost with a minimum of additional parts.  
           [0034]    Finally, there is provided, in accordance with the invention, a method for the operation of a fuel cell system comprising a heat exchanger with at least one fan which produces a cooling air flow through the heat exchanger and with the a fuel cell arrangement fed with compressed air from a compressor, characterized in that at least a part of the cooling air flow is supplied to the fuel cell arrangement, and optionally to a reforming device connected in front of the fuel cell arrangement, for the starting of the fuel cell system and/or for the maintenance of operation in low load ranges, for example, during idling, during loss of speed by rolling or during overrun operation. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0035]    The invention will be explained in more detail in the following with reference to embodiments and to the drawings in which:  
         [0036]    [0036]FIG. 1A shows an exploded illustration of a cooling fan module in accordance with the invention for a vehicle;  
         [0037]    [0037]FIG. 1B shows a perspective illustration of the assembled module of FIG. 1A in which the air branching device is located in a first operating position in which no pronounced branching off of air takes place;  
         [0038]    [0038]FIG. 1C corresponds to FIG. 1B but shows the air branching device in a second position in which air is branched off;  
         [0039]    [0039]FIG. 2 shows a schematic side view of the module of FIG. 1C in a slightly modified form and connected to a fuel cell system;  
         [0040]    [0040]FIG. 3A shows an end view of a further cooling fan module in accordance with the invention with an air branching device in the form of an iris diaphragm in the closed, air branching position;  
         [0041]    [0041]FIG. 3B shows a representation similar to FIG. 3A but with the air branching device in the first, open position in which no branching off of air takes place;  
         [0042]    [0042]FIG. 3C shows a side view of the embodiment of FIGS. 3A and 3B;  
         [0043]    [0043]FIG. 4A shows an end view of a further cooling fan module in accordance with the invention seen from the downstream side with an air branching device in the form of a roller blind in a partly open state;  
         [0044]    [0044]FIG. 4B shows a representation similar to FIG. 4A, but with the roller blind in the second closed position in which branching off of air takes place;  
         [0045]    [0045]FIG. 4C shows a side view of the cooling fan module of FIGS. 4A and 4B;  
         [0046]    [0046]FIG. 5A shows an end view of a further variant of a cooling fan module in accordance with the invention at the downstream side with an air branching device in the form of a roller shutter being used and being shown here in the closed state; and  
         [0047]    [0047]FIG. 5B shows a representation similar to FIG. 5A, but in the first open operating state of the roller shutter. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0048]    [0048]FIG. 1A shows in a perspective, highly schematic representation a cooling fan module  10  consisting of two pusher fans  12  which press air through a heat exchanger  14  in order to cool a liquid, which is not shown but which flows through the heat exchanger  14 .  
         [0049]    An air guiding housing  16 , here in the form of a rectangular box, carries a plurality of pivotally hinged plates  18  in the form of a louver window and covered over in the lower region by an air collecting box  20 , with the air collecting box  20  opening into a duct  22  which, in accordance with FIG. 2, leads directly or indirectly to the fuel cells, as will be explained in more detail later. The plates  18  form an air branching device  19 .  
         [0050]    [0050]FIG. 1B shows the module of FIG. 1A in the assembled state, and it can be recognized that this is a compact, space-saving design. At the upper left-hand side of the air guiding housing, which is formed as a frame, there is a positioning motor  24  which is connected to the individual plates  18  via a lever arm  26  and connecting rod  28  and which can move or pivot the plates from a first open operating position, in accordance with FIG. 1B, in which at least substantially no branching off of air takes place, into a second closed position shown in FIG. 1C in which the individual plates  18  close in an air-tight manner against one another and against the air guiding housing  16 , so that the air delivered by the fans  12  is forced to flow into the air collecting box  20  and this air passes from there via the duct  22  to the fuel cells.  
         [0051]    In a simplified embodiment, the plates  18  and the motor  24  are omitted and the wall of the air collecting box forms a fixedly disposed guide wall forming the air branching device. A plurality of different embodiments with fixedly arranged guide walls can also be considered.  
         [0052]    [0052]FIG. 2 shows essentially the same design of the cooling fan module of the invention as in FIGS.  1 A- 1 C, but with some differences. First of all, FIG. 2 makes it clear that the two cooling fans  12  are connected to the heat exchanger  14  via a housing  30 , so that the total quantity of air which is conveyed by the pusher fans  12  has to flow through the heat exchanger  14 . In this example, the outlet  22  of the air collecting box  20  is led out at the rear of the air collecting box and not at the side as in the example of FIG. 1. The outlet  22  leads into a duct  32  which leads to an air inlet  34  of the fuel cell arrangement  36 . Within the fuel cell arrangement  36  there is in known manner an air distribution passage to which both the air inlet  34  and the air inlet  38 , which is connected to the outlet of the air compressor  40 , lead.  
         [0053]    In the normal operation of the fuel cell arrangement, the compressor  40  sucks in air via the inlet  42 , with an air filter, for example, being positioned upstream of the inlet  42 , compresses the air and then delivers it as compressed air via the inlet  38  to the fuel cell arrangement  36 .  
         [0054]    In order to avoid an undesired reverse flow via the duct  32  on operation of the compressor  40 , the duct  32  is provided with a valve flap  44  controllable by a control  42 . The valve flap  44  shown in the open position in FIG. 2 can, however, be moved via the control  42  into a closed position in order to prevent the aforementioned reverse flow.  
         [0055]    A correspondingly controllable valve flap can also be arranged in the region of the air inlet  38  or of the inlet  42  in order to prevent air escaping via the compressor  40  when the fuel cell arrangement is fed by the pushed fans  12 .  
         [0056]    The valve flap  44  can be omitted when the duct is led, as indicated by  32 ′, into the air induction pipe  42  of the compressor. The air inlet  34  of the fuel cell arrangement  36  is then superfluous. It is, however, eventually necessary to provide a valve in the region of the air induction tube  42  upstream of the mouth of the line  32 ′ in order to avoid an undesired loss of air here when operating the pusher fan prior to taking the compressor into operation.  
         [0057]    The reference numeral  46  indicates an air filter which in this example is arranged in the duct  32 . As an alternative, an air filter  46 ′ could be accommodated in the air collecting box  20 .  
         [0058]    On starting a vehicle with the fuel cell system of FIG. 2, the motor  24  is first energized in order to close the louver plates  18 , i.e., to bring them into the position of FIG. 1C. At the same time the valve  44 , if present, is opened and the pusher fans  12  operated by the low voltage onboard battery are switched on so that the compressed air produced by the pusher fans  12  passes via the housing  30 , the heat exchanger  14 , the air guiding housing  16 , and the air collecting box  20  into the duct  32  and thus to the fuel cells  36 . Should the duct be lead into the compressor inlet, as shown at  32 ′, the compressed air passes from the pusher fans via the compressor  40  into the fuel cell arrangement  36 . At the same time, hydrogen or a synthesized hydrogen-rich gas is supplied to the fuel cell arrangement  36  via the hydrogen inlet  48 . The fuel cell arrangement  36  then starts to produce power.  
         [0059]    As soon as the quantity of power which is generated is sufficient to drive the motor (not shown) which drives the compressor  40 , this motor is set operating. The compressor  40  then delivers the required quantity of air in order to keep the fuel cell arrangement  36  operating and to produce the necessary power.  
         [0060]    As soon as the compressor  40  delivers sufficient air to the fuel cell arrangement  36 , the motor  24  can be controlled in order to bring the louver plates  18  into the open position of FIG. 1B. The valve flap can be brought into a position in which it closes the duct  32 , so that no air losses arise due to reverse flow via the duct  32 . Instead of using an electrically controlled valve, i.e., instead of using a valve flap, this can also be designed as a non-return valve. This also applies to a valve which may possibly be provided in the region of the inlet  38  or in the air supply to the compressor  40 , in order to avoid air losses on feeding the fuel cell arrangement  36  by the pusher fans  12 .  
         [0061]    Although an air collecting box is used in the embodiments of FIGS. 1 and 2, one can dispense with such an air collecting box. Instead of this, the air outlet  22  can be led directly out of the air guiding housing  16  or out of the housing  30 . The louver plates  18  or other branching off devices must then cover over the entire outlet side of the air guiding housing  16  or of the heat exchanger. When the air outlet is led out of the housing  30 , the branching off device could be arranged in front of the heat exchanger and fully cover over its inlet side.  
         [0062]    These further possibilities of placement of the air outlet are indicated in FIG. 2 by  22 ′ and  22 ″.  
         [0063]    FIGS.  3 A- 3 C show an alternative form of the air branching device. In this example, the air branching device  50  again consists of plate  18 ′. These are, however, arranged in the manner of an iris diaphragm. FIG. 3A shows the closed position of the iris diaphragm. One notes that the radially inner ends of the plates  18 ′ form an open circular orifice  52  which lies opposite to the inlet of an air collecting cone  54  (FIG. 3B) provided with an outlet  22 ″′. The iris diaphragm is so designed that the radially inner ends of the plates  18 ′ directly sealingly contact the air collecting cone  54  directly adjacent to the opening, so that the compressed air produced by the pusher fans  12  is collected by the air collecting housing  16  and forced into the air collecting cone  54  from which it passes via the air outlet  22 ″′ into a duct such as  32  or  32 ′.  
         [0064]    [0064]FIG. 3B shows the fully-open position of the iris diaphragm which bounds a circular, ring-shaped air outlet  56  for the air which passes through the heat exchanger  14 . In this example, it can be advantageous to operate with only one circular pusher fan  12 . In this example, the plates  18 ′ are moved by the motor  24 ′ between the positions of FIGS. 3A and 3B. In a modified variant, the plates  18 ′ of the iris diaphragm could close completely and an air outlet  22 ′ or  22 ″ could be provided as in the embodiment of FIG. 2.  
         [0065]    [0065]FIG. 4 shows an alternative embodiment in which an air branching device in the form of a roller blind  60  is used at the outlet side of the air guiding housing  16 . This roller blind  60  is a flexible, impermeable membrane  62  which can be rolled up onto an upper spring-loaded cylinder  64 , with the spring loading being so designed that it endeavors to move the roller blind in the direction of the arrow  66  into a fully-open position. At the lower side of the roller blind  60  in FIG. 4A there are two cables  68  which can be rolled up onto a cylinder  70  in the lower region of the air guiding housing  16 , the cylinder  70  being driveable by a motor  72 .  
         [0066]    The motor  72  can unwind the roller blind  60  from the upper spring-loaded cylinder  64  by rotation of the cylinder  70  around the axis  76  in accordance with the arrow  74 , with the cylinder  64  being rotatably arranged about its longitudinal axis  78 .  
         [0067]    [0067]FIG. 4A shows an intermediate position in which the lower edge of the roller blind  60  has started to cover over the air outlet side of the air guiding housing, whereas FIG. 4B shows the fully-closed position.  
         [0068]    The motor  72  is used in order to bring the roller blinds  60  downwardly into the closed position of FIG. 4B, where the blind can be held by a non-illustrated latch, for example by a pin, which is actuated by a solenoid. As soon as the fuel cell arrangement produces sufficient power in order to drive the compressor  40 , the latch is released, for example by interrupting the supply of current to the solenoid, and the spring-loaded cylinder  64  then serves to wind up the roller blind so that this moves back into the fully-open position (not shown).  
         [0069]    [0069]FIGS. 5A and 5B show a similar arrangement except that here an air branching device  84  is used with plates  18 ′ in the form of a roller shutter. In this example, the roller shutter is drawn downwardly via cables  68 ′ by a spring-loaded cylinder  80  in order to attain the closed position of FIG. 5A in which the lowermost plate  18 ″ sealingly closes against the lower edge of the air collecting box  20 . For the opening of the roller shutter, the motor  72  is energized. It then turns the cylinder  82  which rolls up the plates until the fully-open position of FIG. 5B is reached. The roller shutter can then be held in this position by a non-illustrated latch, so that the motor  72  does not need to be permanently energized.  
         [0070]    Although the device of the invention is primarily used for the starting up of the fuel cell system, it could, under some circumstances, be used when it is only necessary to maintain the operation of the fuel cells, so that the vehicle can immediately start again when operating in a low load region, for example, during idling at a traffic light, in overrun operation or when loosing speed by rolling. The possibility of switching off the motor for the compressor in these operating phases can contribute to noise reduction.