Abstract:
A fuel-supply unit for a motor vehicle has a fuel container ( 2 ) that has several chambers ( 6, 7 ). The unit has a transfer pump ( 5 ) that is located inside the fuel container ( 2 ) for exclusively supplying ejector pumps ( 9, 10 ), which are positioned in the chambers ( 6, 7 ), with fuel as the pumping fluid. A primary fuel pump ( 4 ) that is located outside the fuel container ( 2 ) supplies an internal combustion engine ( 1 ) of the motor vehicle with fuel. The transfer pump ( 5 ) is operated discontinuously to prevent unnecessary power consumption.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a U.S. national stage application of International Application No. PCT/EP2006/050116 filed Jan. 10, 2006, which designates the United States of America, and claims priority to German application number 10 2005 008 380.3 filed Feb. 23, 2005, the contents of which are hereby incorporated by reference in their entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The invention relates to a fuel supply device for a motor vehicle having a fuel container and having a main fuel pump which is arranged outside the fuel container and has the purpose of sucking in fuel from the fuel container and of feeding the fuel to the internal combustion engine. 
       BACKGROUND 
       [0003]    Such fuel supply devices are frequently used in contemporary motor vehicles in conjunction with fuel containers having a single chamber, and said fuel supply devices are known from practice. In contemporary fuel supply devices, fuel which is not required by the internal combustion engine is frequently fed back in a non-pressurized state into the fuel container. For this reason, it is not possible to connect to the return line any suction jet pumps which can feed fuel from a secondary chamber of the fuel container into a main chamber. However, fuel containers which have a plurality of chambers are frequently used, for example in motor vehicles with all wheel drive. 
         [0004]    The possibility of using a transfer pump for supplying suction jet pumps arranged in the fuel container has already been considered. Continuous operation of the transfer pump results in a continuous noise level, a high level of power consumption and also in a short service life. 
       SUMMARY 
       [0005]    A fuel supply device of the type mentioned at the beginning can be designed in such a way that it permits operation in conjunction with a fuel container which has a plurality of chambers. 
         [0006]    According to an embodiment, a fuel supply device for a motor vehicle may comprise a fuel container, a main fuel pump which is arranged outside the fuel container for sucking in fuel from the fuel container and feeding the fuel to an internal combustion engine, suction jet pumps for feeding fuel from the chambers of the fuel container to an intake port of the main fuel pump, the suction jet pumps being arranged in said chambers, and an electrically driven transfer pump arranged within the fuel container, wherein a pressure side of the transfer pump is connected to nozzles of the suction jet pumps, and the transfer pump is switched discontinuously. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The invention permits numerous embodiments. In order to clarify its basic principle further, two of said principles are illustrated in the drawing and will be described below. In said drawing: 
           [0008]      FIG. 1  is a schematic illustration of a fuel supply device according to an embodiment, 
           [0009]      FIG. 2  is a schematic view of a circuit diagram relating to the means of actuating a transfer pump of the fuel supply device from  FIG. 1 , and 
           [0010]      FIG. 3  is a further schematic illustration of the fuel supply device according to an embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]    According to an embodiment, suction jet pumps for feeding fuel from the chambers of the fuel container to an intake port of the main fuel pump are arranged in said chambers, in that an electrically driven transfer pump is arranged within the fuel container, and in that a pressure side of the transfer pump is connected to nozzles of the suction jet pumps, and in that the transfer pump is switched discontinuously. 
         [0012]    As a result of this configuration, the transfer pump permits a plurality of suction jet pumps to be supplied with fuel as the propellant and makes available the anticipated propellant pressure for the suction jet pumps. The fuel which is distributed in different chambers of the fuel container is therefore reliably fed to the intake port of the main fuel pump. Fuel which is possibly returned from the internal combustion engine can in this context be returned in an nonpressurized state into the fuel container at any desired point. The returned fuel is preferably fed to the intake port. An operating mode of the fuel supply system according to an embodiment which is particularly convenient for the users of the motor vehicle can be ensured if the transfer pump is switched discontinuously. As a result of this configuration, the transfer pump is switched off at anticipated times, which results not only in a reduction in the noise level caused by the transfer pump but also in lowering of the power consumption and in a long service life of the transfer pump. 
         [0013]    The mounting of the fuel supply device according to an embodiment in the fuel container is particularly easy if the transfer pump and the intake port of the main fuel pump are arranged in a common surge pot. As a result, the transfer pump and the surge pot can be premounted as a premountable unit outside the fuel container. 
         [0014]    According to another embodiment, reliable supply of fuel to the transfer pump can be easily ensured if the suction jet pumps open into the common surge pot. 
         [0015]    Particularly low power consumption of the transfer pump can be easily ensured according to another embodiment if the transfer pump is controlled by means of filling level sensors which are arranged in the chambers of the fuel container. As a result of this configuration, the transfer pump remains permanently inactive when, for example, the fuel container is full and the fuel can flow independently of the chambers inside the fuel container. If the fuel is separated from the chambers when the fuel container is virtually empty, the transfer pump is switched on only when there is too little fuel at the intake port of the main fuel pump but sufficient fuel in another chamber. As a result, it becomes possible to control the transfer pump in a demand-dependent way in accordance with the filling levels of the fuel in the individual chambers. 
         [0016]    Controlling the transfer pump by means of a level switch contributes to reducing the structural complexity of the fuel supply device according to an embodiment. As a result, the transfer pump remains continuously in the switched off state if sufficient fuel is present in the region of the intake port. Such level switches are generally known and they close or interrupt an electrical contact when the fuel exceeds or drops below a filling level. 
         [0017]    The level switch is preferably arranged within the surge pot and/or within a connection of the chambers of the fuel container. As a result, it is possible to sense whether fuel is present near to the intake port of the main fuel pump or whether fuel can overflow from one chamber to the other chamber. 
         [0018]    According to another advantageous development, the level switch is structurally particularly simple if it is embodied as a float switch. 
         [0019]    The interruption of the feeding of the transfer pump, that is to say when sufficient fuel is present in the chamber which has the intake port of the main fuel pump, requires complex sensing and evaluation of filling levels in the fuel container. According to another embodiment, the discontinuous switching of the transfer pump requires particularly little expenditure if the transfer pump has an intermittent switching mode and if the intermittent switching mode is designed to generate an alternating power supply to the transfer pump for successive time periods. Such an intermittent switching mode permits clocked switching of the transfer pump so that an anticipated time period in which the transfer pump is operating is followed by a further anticipated time period in which the transfer pump is switched off. 
         [0020]    According to another embodiment, it is easy to ensure that the suction jet pumps are fed sufficiently if the intermittent switching mode is the ratio of successive time periods of up to 1 to 10 or 20, wherein the power supply to the transfer pump is interrupted in the relatively long time period. 
         [0021]    According to another advantageous development, the discontinuous switching of the transfer pump is structurally particularly simple if the transfer pump has an electronic control unit. 
         [0022]    Connecting the electronic control unit to a relay which is arranged in a power supply of the transfer pump or a transistor circuit contributes to further simplifying the switching of the transfer pump. 
         [0023]    If the control of the transfer pump fails, it is easily possible to ensure a sufficient supply of fuel to the main fuel pump if the relay or the transistor circuit causes the transfer pump to be supplied with power in the nonactuated state. This ensures an emergency operating property of the fuel supply system according to an embodiment. 
         [0024]      FIG. 1  is a schematic view of a fuel supply device for supplying fuel to an internal combustion engine  1 , which operates accordingly to the diesel principle, of a motor vehicle. The fuel supply device has a main fuel pump  4  which sucks in fuel via an intake port  3  which projects into a fuel container  2 , and a transfer pump  5  which feeds fuel within the fuel container  2  to the intake port  3  of the main fuel pump  4 . This main fuel pump  4  can be, for example, a mechanically driven diesel high pressure pump. The fuel container  2  is embodied as what is referred to as a saddle tank with two chambers. The main fuel pump  4  is arranged outside the fuel container  2 , while the intake port  3  and the transfer pump  5  are arranged inside a surge pot  8  which is prestressed against the bottom of the fuel container  2 . Suction jet pumps  9 ,  10  which are supplied with fuel as a propellant from the transfer pump  5  and which feed fuel from the chambers  6 ,  7  into the surge pot  8  are arranged in the chambers  6 ,  7 . Furthermore, filling level sensors  11 ,  12  for measuring the filling level of fuel in the respective chambers  6 ,  7  are arranged in the chambers  6 ,  7 . 
         [0025]      FIG. 2  is a schematic circuit diagram relating to the means of actuating the transfer pump  5  from  FIG. 1 . The transfer pump  5  is connected to a power source  15  via a relay  14  which can be actuated by a control unit  13 . In the illustrated basic state, the connection is formed between the transfer pump  5  and the power source  15  so that if the control unit  13  fails the transfer pump  5  is continuously supplied with electrical current and it is ensured that fuel is fed to the intake port  3  illustrated in  FIG. 1 . The control unit  13  has an intermittent switching mode  16  according to which the relay  14  is actuated after an anticipated first time period and the power supply to the transfer pump  5  is interrupted for an anticipated second time period. This second time period is followed in turn by the first time period in which the transfer pump  5  is actuated. The ratio of the first time period to the second time period is, for example, 1 to 10 so that the transfer pump  5  is switched off for most of the time. Furthermore, the control unit  13  has an input  17  for signals of the filling level sensors  11 ,  12 . As a result, the transfer pump  5  can, for example, be switched off if the fuel container  2  is completely filled with fuel and fuel can overflow from one chamber  6  into the other chamber  7 . Alternatively, the control unit  13  can also evaluate the signals of the filling level sensors  11 ,  12  in the individual chambers  6 ,  7  and activate the transfer pump  5  only if the chamber  5  which has the surge pot  8  has virtually no fuel but other chambers have sufficient fuel. 
         [0026]      FIG. 3  shows a further embodiment of the fuel supply device which differs from that in  FIG. 1  only in that a level switch  18 ,  19  is arranged at the upper edge of the surge pot  8  and within the fuel container  2 , respectively. The level switches  18 ,  19  are embodied as float switches. The transfer pump  5  can be actuated using the signals from the level switches  18 ,  19  in that, for example, the transfer pump  5  is continuously switched off when the surge pot  8  is filled with fuel. If the filling level in the surge pot  8  drops below the filling level which is provided for the switching of the level switch  18  in the surge pot  8 , the transfer pump  5  can be activated. The level switch  19  in the fuel container  2  makes it possible to sense whether fuel can flow to and fro between the chambers  6 ,  7 . In this case, it is not necessary to activate the transfer pump  8  and it is possible to prevent it. Here, as in the first embodiment, the transfer pump  8  can be activated with the control unit  13  according to  FIG. 2  in an intermittent switching mode or a timed switching mode in which the transfer pump  8  is activated for a minimum time period of, for example, 60 seconds. For this purpose, signals from the level switches  18 ,  19  are fed to the control unit  13  via the input  17 .