Abstract:
A fuel cell system includes a fuel cell and an ejector. The ejector includes a nozzle portion having openings provided at its distal and proximal ends for injecting drive-stream gas; a diffuser portion provided on a distal end side of the nozzle portion for drawing in auxiliary gas by negative pressure which is generated in the drive-stream gas by injection from the nozzle portion so as to join the auxiliary-stream gas together with the drive-stream and discharge the drive-stream gas and the auxiliary gas; a needle slidably inserted into an interior of the nozzle portion in an axial direction of the nozzle portion for adjusting an opening area of the nozzle portion in accordance with an inserted position thereof; a drive unit for moving the needle axially; and an auxiliary stream gas introducing portion including at least two openings for introducing the auxiliary-stream gas into the diffuser portion therefrom.

Description:
[0001]    The present invention claims foreign priority to Japanese patent application No. P.2005-092325, filed on Mar. 28, 2005, the contents of which is incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to an ejector which has a configuration in which an auxiliary-stream gas is made to join a drive-stream gas for discharge the drive-stream gas and the auxiliary-stream gas therefrom. 
         [0004]    2. Description of the Background Art 
         [0005]    There has been proposed a technique in which an ejector is used as a hydrogen circulating pump in a fuel cell system. The ejector is such as to have a construction in which circulating hydrogen is drawn in for re-supply by making use of negative pressure produced by injecting a high-pressure fluid from a jet nozzle. 
         [0006]    When the ejector so constructed is used, the circulating capability is limited by the diameter of the jet nozzle, and hence, there occurs a case where the ejector is not suitable for a fuel cell system having a large flow rate range such as one for a motor vehicle. 
         [0007]    On the contrary, Japanese Patent Unexamined Publication No. JP-A-8-338398 proposes a technique in which the opening area of an injection nozzle is adjusted by axially moving a cylindrical adjusting rod (a needle). 
         [0008]    Incidentally, depending on the production accuracy of constituent components of an ejector such as a needle and its guide member or an actuator for moving the needle, a needle set in a nozzle is caused to deviate minutely from an axial direction thereof. In the event that a configuration such as seen in the aforementioned technique is adopted for the ejector like this in which an auxiliary-stream gas is caused to simply hit the needle, there is caused a problem in the drawing force and drawing amount of the auxiliary stream. 
         [0009]    The problem will be described using  FIGS. 4 ,  5 .  FIGS. 4 and 5  are drawings which illustrate a main part of a conventional ejector to describe the problem inherent therein. Firstly, in the event that a distal end portion of a needle  33  is displaced in a direction in which the distal end portion moves away from an auxiliary-stream gas (namely, in a direction which follows an arrow A in  FIG. 4 ), an opening area of a location of a distal end portion of a nozzle  32  which lies near the auxiliary-stream gas (namely, a lower region of the distal end portion of the nozzle  32 ) is increased. As a result, a drawing force exerted on the auxiliary-stream gas by a driven steam of gas is increased, whereby the flow rate of the auxiliary-stream gas is increased excessively (refer to FIG.  4 ). 
         [0010]    In contrast, in the event that the distal end portion of the needle  33  is displaced in a direction in which the distal end portion approaches the auxiliary-stream gas (namely, in an opposite direction to an arrow A in  FIG. 5 ) due to the pressure of the auxiliary-stream gas, an opening area of a location of the distal end portion of the nozzle which lies away from the auxiliary-stream gas (namely, an upper region of the distal end portion of the nozzle  32 ) is increased. As a result, the drawing force exerted on the auxiliary-stream gas by the drive-stream gas is decreased, whereby the flow rate of the auxiliary-stream gas is decreased excessively (refer to  FIG. 5 ). 
         [0011]    Thus, there exists a problem where an accurate control of the drawing force and drawing amount of the auxiliary-stream gas becomes difficult to be implemented. In particular, in a case where an ejector is installed in a fuel cell system in which an unreacted off-gas is circulated, the unreacted off-gas constitutes an auxiliary stream, and since the flow rate and flow velocity of the auxiliary stream can affect power generating conditions, controlling the flow rate and flow velocity of the auxiliary stream becomes crucial to secure a desired power generation performance, as well. While it is considered as a means for attaining this to configure the needle to follow precisely the axis thereof in a perfect fashion when it slides, there is caused a problem where since a severe accuracy which is required for production deteriorates the productivity, the attempt is unrealistic. 
       SUMMARY OF THE INVENTION 
       [0012]    Consequently, an object of the invention is to provide an ejector which can control the flow rate and flow velocity of the auxiliary-stream gas with good accuracy. 
         [0013]    According to a first aspect of the invention, there is provided an ejector comprising: 
         [0014]    a nozzle portion (for example, a nozzle  32  in an embodiment which will be described later on) having openings provided at a distal end and a proximal end thereof, respectively, for injecting drive-stream gas; 
         [0015]    a diffuser portion (for example, a diffuser  31  in the embodiment which will be described later on) provided on a distal end side of the nozzle portion for drawing in auxiliary gas by negative pressure which is generated in the drive-stream gas by injection from the nozzle portion so as to join the auxiliary-stream gas together with the drive-stream and discharge the drive-stream gas and the auxiliary gas; 
         [0016]    a needle (for example, a needle  33  in the embodiment which will be described later on) slidably inserted into an interior of the nozzle portion in an axial direction of the nozzle portion for adjusting an opening area of the nozzle portion in accordance with an inserted position thereof; 
         [0017]    a drive unit (for example, a solenoid  11  in the embodiment) for moving the needle axially; and 
         [0018]    an auxiliary stream introducing portion (for example, an auxiliary-stream gas introducing portion  13  in the embodiment) comprising at least two openings for introducing the auxiliary-stream gas into the diffuser portion therefrom. 
         [0019]    According to the first aspect of the invention, since the auxiliary-stream gas is introduced from at least two openings in the auxiliary stream introducing portion, the auxiliary-stream gas is allowed to be introduced from a plurality of directions relative to the needle, and as a result, the pressure exerted on the needle from the auxiliary-stream gas can be dispersed relative to the axial direction of the needle. Consequently, deviations in drawing force and drawing amount triggered by the deviation of the needle from the axial direction thereof can be suppressed, whereby since the opening area and opening region of the nozzle portion can be maintained in originally designed states, the drawing force and drawing amount of the auxiliary-stream gas can be controlled with good accuracy without being affected by the deviation of the needle from the axial direction thereof. 
         [0020]    According to a second aspect of the invention, as set forth in the first aspect of the present invention, it is preferable that the ejector further comprising a buffer chamber provided on an upstream side of the auxiliary stream introducing portion, 
         [0021]    wherein the auxiliary-stream gas is adopted to be introduced into the plurality of openings from the buffer chamber. 
         [0022]    According to the structure, since an auxiliary-stream gas can be distributed to each of the openings via the buffer chamber without having to have a configuration in which piping is individually connected to each auxiliary stream introducing portion, auxiliary-stream gas can easily be supplied to the diffuser portion from multiple directions. 
         [0023]    According to a third aspect of the invention, as set forth in the first aspect of the present invention, it is preferable that the ejector is used on a fuel cell system. 
         [0024]    According to the structure, since the drawing force and drawing amount of auxiliary-stream gas can be controlled with good accuracy regardless of the shaft position of the needle, an easy and fine control of the flow of fuel cell system gas can be implemented, whereby the power generation stability of the fuel cell can be enhanced. 
         [0025]    According to a fourth aspect of the present invention, as set forth in the first aspect of the present invention, it is preferable that the openings of the auxiliary stream introducing portion are arranged along with a circumferential direction of the diffuser portion. 
         [0026]    According to a fifth aspect of the present invention, as set forth in the first aspect of the present invention, it is preferable that the openings of the auxiliary stream introducing portion are arranged in point symmetry manner relative to a central axis of the needle. 
         [0027]    According to the first aspect of the invention, since the opening area and opening region of the nozzle portion can be maintained in the originally designed states, the drawing force and drawing amount of the auxiliary-stream gas can be controlled with good accuracy. 
         [0028]    According to the second aspect of the invention, the auxiliary-stream gas can easily be supplied to the diffuser portion from multiple directions. 
         [0029]    According to the third aspect of the invention, the power generation stability of the fuel cell can be enhanced. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0030]      FIG. 1  is a drawing which illustrates the configuration of a fuel cell system which includes a variable flow rate ejector according to an embodiment of the invention; 
           [0031]      FIG. 2  is a side sectional view of the variable flow rate ejector according to the embodiment of the invention; 
           [0032]      FIG. 3  is an explanatory drawing which illustrates the flow of auxiliary-stream gas of the variable flow rate ejector according to the embodiment of the invention; 
           [0033]      FIG. 4  is a drawing depicting a main part of a conventional ejector which illustrates a problem inherent therein; and 
           [0034]      FIG. 5  is a drawing depicting the main part of the conventional ejector which illustrates a problem inherent therein. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0035]    Hereinafter, a variable flow rate ejector according to an embodiment of the invention will be described by reference to the accompanying drawings.  FIG. 1  is a drawing which shows the configuration of a fuel cell system  20  including a variable flow rate ejector  10  according an embodiment of the invention, and  FIG. 2  is a side sectional view of the variable flow rate ejector  10  according to the embodiment of the invention. The variable flow rate ejector  10  according to the embodiment of the invention is provided in the fuel cell system  20  which is installed on a vehicle such as an electric vehicle, and this fuel cell system  20  is made up of the variable flow rate ejector  10 , fuel cells  21 , an oxidant supply unit  24 , a heat exchanger  25  and a water separator  26 . 
         [0036]    The fuel cell  21  is made up of a stack which includes a plurality of stacked cells, each formed by holding a solid polymer electrolyte membrane, which is, for example, a solid polymer ion exchange membrane by an anode and a cathode from both sides thereof and includes a fuel electrode to which, for example, hydrogen is supplied as a fuel; and an air electrode to which, for example, air containing oxygen is supplied as an oxidant. 
         [0037]    An air supply port  21   a  into which air is supplied from the oxidant supply unit  24  and an air discharge port  21   b  having provided therein an air discharge valve  28  for discharging air or the like in the air electrode to the outside are provided on the air electrode. On the other hand, a fuel supply port  21   c  to which hydrogen is supplied and a fuel discharge port  21   d  for discharging hydrogen or the like in the fuel electrode to the outside are provided on the fuel electrode. 
         [0038]    The oxidant supply unit  24  is made up of, for example, a compressor and is controlled in response to a load applied to the fuel cell  21 , an input signal from an accelerator pedal (not shown) and the like, so as to supply air to the air electrode of the fuel cell  21  via the heat exchanger  25 . The heat exchanger  25  cools air sent from the oxidant supply unit  24  down to a predetermined temperature for supply to the fuel cell  21 . 
         [0039]    Hydrogen, which functions as fuel, is supplied from the fuel supply port  21   c  to the fuel electrode of the fuel cell  21  via the variable flow rate ejector  10 . Furthermore, a discharged fuel which is discharged from the fuel discharge portion  21   d  of the fuel cell  21  is introduced into the variable flow rate ejector  10  through a check valve  29  after water is removed therefrom at the water separator  26 , and as will be described later on, fuel and the discharged fuel discharged from the fuel cell  21  are made to join or mix with each other for supply to the fuel cell  21 . Note that water separated from the discharged fuel at the water separator  26  is discharged to the outside by opening a drain valve  30 . 
         [0040]    The variable flow rate ejector  10  according to the embodiment of the invention is such as to make a discharged fuel circulated from the fuel cell  21  join a stream of fuel gas supplied from the fuel supply unit  22  by making use of the stream of fuel gas so supplied and to control the flow rate of fuels supplied to the fuel cell  21  based on an air pressure Pair on the air electrode side of the fuel cell  21  which is detected by a pressure sensor  7  and a fuel pressure Pfuel on the fuel electrode side of the fuel cell  21  which is detected by a pressure sensor  6  when receiving a control instruction from an ECU  5  and is configured to include, as shown in  FIG. 2 , a diffuser  31 , a nozzle  32  and a needle  33 . 
         [0041]    A fluid passageway  43  is formed in the diffuser  31  in such a manner as to penetrate axially the diffuser  31  on a downstream side thereof. The fluid passageway  43  has a throat portion  44  where an inside diameter thereof becomes minimum at a position along the length thereof, and a throttle portion  45  is provided upstream of the throat portion  44  which has an inner circumferential surface which diametrically contracts gradually and continuously as it proceeds downstream, and a diametrically expanding portion  46  is provided downstream of the throat portion  44  which has an inner circumferential surface which diametrically expands gradually and continuously as it proceeds downstream. 
         [0042]    The nozzle  32  is provided in an interior of the diffuser  31  in such a manner as to protrude coaxially with the diffuser  31  towards an upstream side of the fluid passageway  43 . 
         [0043]    A fluid passageway  51  is formed in an interior of the nozzle  32  in such a manner as to extend along an axial direction of the nozzle  32 . An inner circumferential surface  32 A, which constitutes a wall surface of the fluid passageway  51 , is formed at a distal end portion of the nozzle  32  in such a manner as to diametrically contract gradually and continuously towards a distal end side thereof (a downstream side of the fluid passageway  51 ). A downstream end of the fluid passageway  51  continues to an opening  52  which opens at a distal end face  32   b  of the nozzle  32 , and an upstream end of the fluid passageway  51  is blocked up by a diaphragm (not shown). A fuel supply pipe (not shown) is connected to the fluid passageway  51  for introducing thereinto fuel supplied from the fuel supply unit  22 . 
         [0044]    The needle  33  is inserted into the interior of the nozzle  32  coaxially with the nozzle  32 , and the needle  33  is held by a needle holding guide (not shown) in such a manner as to slide in an axial direction which is coaxial with the nozzle  32 . Here, an outer circumferential surface of the needle  33  is formed at a distal end portion of the needle  33  in such a manner as to diametrically contract gradually and continuously as it extends towards a distal end side thereof. Namely, when the needle  33  slides in the axial direction in the interior of the nozzle  32 , a protruding amount of the distal end portion of the needle  33  which protrudes from the opening  52  of the nozzle  32  is changed. In association with this, an opening area of a gap between the inner circumferential surface of the nozzle  32  and the outer circumferential surface of the needle  33  is changed, whereby the flow rate of fuel that is injected into an auxiliary stream chamber  48  from the opening  52  of the nozzle  32  can be adjusted. 
         [0045]    Note that the needle holding guide, which holds the needle  33  in such a manner as to slide relative to the axial direction, is formed into, for example, an annular disc shape having an appropriate through hole through which fluid can pass, and the needle  33  is inserted through a needle insertion hole which penetrates the annular disc in the axial direction. In addition, the needle  33  is connected electrically and mechanically to a solenoid  11 , so that the needle  33  is configured to be moved back and forth in the axial direction in response to ON/OFF operations of the solenoid  11 . 
         [0046]    Additionally, an auxiliary-stream gas introducing portion  13  having a plurality of auxiliary-stream gas introducing holes  12  is formed in the auxiliary stream chamber  48  at a location which faces the outer circumferential surface of the nozzle  32 . This auxiliary-stream gas introducing portion  13  is connected to an auxiliary stream introducing pipe  49 , which communicates with a fuel off-gas discharge path, via a buffer chamber  14  which is formed on an outer circumferential side of the auxiliary-stream gas introducing portion  13 . For an example, as shown in  FIG. 2 , pluralities of the auxiliary stream gas introducing holes  12  are arranged along with a circumferential direction of the diffuser  31 . 
         [0047]    The fuel cell system  20  including the variable flow rate ejector  10  according to the embodiment of the invention is configured as has been described heretofore. Next, the operation of the variable flow rate ejector  10  will be described.  FIG. 3  is an explanatory drawing which illustrates the flow of an auxiliary-stream gas in the variable flow rate ejector according the embodiment of the invention. 
         [0048]    In this variable flow rate ejector  10 , a discharged fuel gas from the fuel cell  21  is supplied thereinto from the auxiliary stream introducing pipe  49  through the plurality of auxiliary-stream gas introducing holes  12  possessed by the auxiliary-stream gas introducing portion  13  via the buffer chamber  14 . In addition, a fuel is supplied into the fluid passageway  51  in the interior of the nozzle  32  from the fuel supply pipe (not shown). Then, the fuel so supplied is injected from the opening  52  of the nozzle  32 , that is, the gap between the nozzle  32  and the needle  33  towards the fluid passageway  43  of the diffuser  31 . As this occurs, negative pressure is produced in the vicinity of the throat portion  44  of the diffuser  31  where a high-velocity fuel stream passes, and fuel auxiliary-stream gas within the auxiliary stream chamber  48  is drawn into the fluid passageway  43  by the vacuum so produced, so as to be mixed with the fuel injected from the nozzle  32  for discharge from a downstream end of the diffuser  31 , whereby the discharged fuel discharged from the fuel cell  21  is circulated via the variable flow rate ejector  10 . 
         [0049]    Thus, since the auxiliary-stream gas (in this case, the discharged fuel gas) is introduced individually from the plurality of auxiliary-stream gas introducing holes  12 , the auxiliary-stream gas is introduced from a plurality of directions relative to the needle  33 . As a result, a pressure that the needle  33  receives from the auxiliary-stream gas can be dispersed relative to the axial direction. Consequently, the deviation in drawing force and drawing amount of auxiliary stream that is triggered by the deviation of the needle  33  from the axial direction thereof can be suppressed, whereby since the opening area and opening region of the nozzle  32  can be maintained in the originally designed states, even in the event that the needle  33  is caused to deviate slightly from the axial direction thereof, the drawing force and drawing amount of auxiliary-stream gas can be controlled with good accuracy. 
         [0050]    In addition, since the auxiliary-stream gas can be distributed individually to the plurality of auxiliary-stream gas introducing holes  12  via the buffer chamber  14 , the auxiliary-stream gas can easily be supplied to the diffuser from multiple directions. For an example, the auxiliary-stream gas introducing holes  12  are disposed in point symmetry relative to a central axis of the needle  33 , whereby the auxiliary-stream gas is dispersed, so as to hit the needle not only from the multiple direction but also in substantially the same amount, thereby making it possible to obtain an advantage where the deviation in position of the needle  33  can be suppressed. The advantage can be achieved by arranging the auxiliary-stream gas introducing holes  12  along with the circumferential direction of the diffuser  31 , as described above. 
         [0051]    In addition, by applying the ejector  10  to the fuel cell system, an easy and fine control of the stream of fuel cell system gas can be implemented, whereby the power generation stability of the fuel cell can be enhanced. Note that a space for the water separator  26  or the like is secured upstream of the ejector  10 , even in the event that the buffer chamber  14  is configured to be provided in the ejector  10 , an effect resulting from a reduction in sucking amount can be suppressed. 
         [0052]    Thus, as has been described heretofore, according to the ejector of the embodiment of the invention, the control of drawing force and drawing amount of auxiliary-stream gas can be implemented with good accuracy. 
         [0053]    Note that the contents of the invention are, of course, not limited to the embodiment. For example, while in the embodiment, the ejector is described as being applied to the fuel cell system, the ejector can be applied to other systems. 
         [0054]    While there has been described in connection with the preferred embodiments of the present invention, it will be obvious to those skilled in the art that various changes and modification may be made therein without departing from the present invention, and it is aimed, therefore, to cover in the appended claim all such changes and modifications as fall within the true spirit and scope.