CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a 35 USC 371 application of PCT/DE 01/00312 filed on Jan. 26, 2001. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   2. Description of the Prior Art 
   The invention is based on a fuel supply system for internal combustion engines, having a fuel tank and a fuel reservoir disposed therein, having means for filling the fuel reservoir with fuel from the tank, and having a fuel line that hydraulically connects the fuel reservoir to the internal combustion engine. 
   Fuel supply systems of this kind are known. The purpose of the fuel reservoir is to assure that the fuel line, which extends into the fuel supply system, aspirates fuel and not air for as long as possible. This is particularly important when the tank is near empty and/or when the vehicle is subject to powerful lateral accelerations so that the contents of the fuel tank are pushed to the side. This effect is achieved in that the fuel reservoir has a relatively small base and a height that corresponds approximately to the height of the fuel tank so that only a relatively small volume of fuel is required to fill the fuel reservoir. This fuel volume is supplied to the fuel reservoir by one or more fuel pumps, which aspirate fuel from the low point(s) of the fuel tank. In order to reduce costs, an electric fuel pump is usually provided inside the fuel reservoir and drives one or more jet pumps disposed in the low point(s) of the fuel tank; the jet pumps supply fuel into the fuel reservoir. This arrangement obviates the need to provide an electric fuel pump in every low point of the fuel tank, which would be expensive and prone to malfunction. 
   In many internal combustion engines, the fuel is supplied by means of a fuel line, which aspirates in a fuel supply system. The fuel is delivered by a fuel-supply pump directly coupled to the engine. This means that at low speeds of the engine, the fuel-supply pump only has a very low delivery capacity. As a result, the fuel-supply pump aspirates little or no fuel from the fuel supply system, which has a disadvantageous effect on the starting behavior of the engine. This also places heavy loads on the starter and starter battery. This operating behavior is particularly problematic when the fuel tank has been run out of gas, when the vehicle is first filled with fuel at the manufacturer, or at low outside temperatures when the performance of the starter battery is reduced. 
   The object of the invention is to produce a fuel supply system for internal combustion engines, which improves the starting behavior of the engine even under unfavorable conditions and consequently contributes to reducing the strain on the starter battery and the starter. 
   This object is attained according to the invention by means of a fuel supply system for internal combustion engines having a fuel tank and a fuel reservoir disposed therein, having means for filling the fuel reservoir with fuel from the fuel tank, and having a fuel line providing a fluid connection between the fuel reservoir and the engine, where the means for filling the fuel reservoir at least sometimes supply fuel into the fuel line. 
   SUMMARY OF THE INVENTION 
   In accordance with this invention, the supplying of fuel to the internal combustion engine does not depend solely on the delivery capacity of the fuel-supply pump of the engine; instead, particularly when starting the engine, the means for filling the fuel reservoir can also be used to supply fuel into the fuel line. This assures that fuel travels through the fuel line to the engine in an extremely short time and consequently improves its starting behavior. Since in essence, only already existing components of the fuel supply system are used, the costs for this measure are very low, which is of particular significance in vehicles that are mass-produced. 
   In one embodiment of the invention, a connecting line is provided between the means for filling the fuel reservoir and fuel line so that the fuel quantity supplied by the means for filling the fuel reservoir can be fed into the fuel line regardless of location and can consequently be adapted to the structural conditions at hand. 
   In one embodiment of the invention, a pressure-holding valve is disposed between the means for filling the fuel reservoir and fuel line so that the working pressure of the jet pumps is always assured. This also assures that the fuel reservoir is filled with fuel from the fuel tank at all times. The pressure holding valve also at least partially prevents the fuel line from emptying out during times when the engine is not running. 
   In another embodiment of the invention, a throttle is provided between the means for filling the fuel reservoir and fuel line, thus permitting a definite distribution of the fuel flow delivered by the fuel pump to the jet pumps and the fuel line. 
   In another advantageous embodiment of the invention, a throttle and a check valve are provided between the means for filling the fuel reservoir and the fuel line so that on the one hand, a definite distribution of the fuel flow delivered by the fuel pump is possible and on the other hand, the fuel line is prevented from emptying out during times when the engine is not running. 
   Another embodiment of the invention provides that a 3/2-port directional-control valve is disposed between the means for filling the fuel reservoir and the fuel line, that in its first switched position, the directional-control valve connects the means for filling the fuel reservoir to the fuel line and in its second switched position, the 3/2-port directional-control valve connects the means for filling the fuel reservoir to the jet pump(s) so that when needed, the entire delivery capacity of the fuel pump is available for filling the fuel line, which achieves a further improvement in the starting behavior of the engine. On the other hand, the entire delivery capacity of the fuel pump can also be used for filling the fuel reservoir. 
   Another embodiment of the invention provides that a 3/3-port directional-control valve is disposed between the means for filling the fuel reservoir and the fuel line, that in its first switched position, the 3/3-port directional-control valve connects the means for filling the fuel reservoir to the fuel line, that in its second switched position, the 3/3-port directional-control valve connects the means for filling the fuel reservoir to the fuel line and the jet pump(s), and that in its third switched position, the 3/3-port directional-control valve connects the means for filling the fuel reservoir to the jet pump(s). This embodiment assures that the fuel pump rapidly fills the fuel line; on the other hand, even when the second switched position is reached, the jet pumps in the fuel tank are also driven, thus preventing a reduction of the fuel level in the fuel reservoir. 
   Another embodiment of the invention provides that the 3/2-port directional-control valve or the 3/2-port directional-control valve is brought into its first switched position in a spring-loaded fashion and that the 2/3-port directional-control valve or the 3/3-port directional-control valve is brought into the second and possibly third switched position, counter to a spring force, through the use of fuel from the means for filling the fuel reservoir. This arrangement assures that after each time that the engine—and therefore also the fuel pump in the fuel supply system—is not in use, the 3/2-port directional-control valve or the 3/3-port directional-control valve is brought into its first switched position so that with the start of delivery by the fuel pump, the fuel line is filled immediately. Because the fuel delivered by the fuel pump actuates the directional-control valves, depending on the pressure level of the fuel delivered by the fuel pump, the spring force, and a throttle that is possibly provided, these directional-control valves travel into the second and possibly third switched position after a particular period of time. This assures that the fuel pump drives the jet pumps shortly after the beginning of fuel delivery and consequently the fuel reservoir is also filled. 
   Another embodiment of the invention provides that the fill level of the fuel reservoir is maintained at least at the fill level of the tank, independent of the means for filling the fuel reservoir so that the fuel line and the fuel pump never aspirate air and on the other hand, a continuous operation of the fuel pump can be avoided. This permits the fuel pump to be designed for a shorter service life, which contributes to reducing costs and to reducing the amount of energy required to drive the fuel pump. 
   Another embodiment of the invention provides that the means for filling the fuel reservoir include an electric fuel pump so that the means for filling the fuel reservoir are inexpensive and easy to activate. 
   Another embodiment of the invention provides that the fuel pump drives at least one jet pump disposed in the vicinity of the low point(s) of the fuel tank in the installation position and that the jet pump(s) feed(s) fuel into the fuel reservoir so that all of the fuel in the fuel tank can be fed into the fuel reservoir in a simple manner. 
   In another embodiment of the invention, the fuel line has a check valve, which prevents the fuel line from emptying out when the engine is not in use. 


   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other advantages and advantageous embodiments of the invention ensue from the following detailed description, taken in conjunction with the drawings, in which: 
       FIG. 1  shows a first exemplary embodiment of a fuel supply system according to the invention, with a pressure-holding valve; 
       FIG. 2  shows a second exemplary embodiment of a fuel supply system according to the invention, with a throttle; 
       FIG. 3  shows a third exemplary embodiment of a fuel supply system according to the invention, with a throttle and a check valve; 
       FIG. 4  shows a fourth exemplary embodiment of a fuel supply system according to the invention, with a 3/3-port directional-control valve in a first switched position; 
       FIG. 5  shows the exemplary embodiment according to  FIG. 4  in a second switched position; 
       FIG. 6  shows the exemplary embodiment according to  FIG. 4  in a third switched position; 
       FIG. 6A  shows the system of  FIG. 4 , with a 3/2-port directional-control valve in a switched position corresponding generally to/the third switched position, and 
       FIG. 7  shows the characteristic curves of the exemplary embodiments according to  FIGS. 1  to  3 . 
   


   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Components that correspond to those in subsequent figures are provided with the same reference numerals; explanations that are given in conjunction with one figure correspondingly apply to the other figures. 
     FIG. 1  schematically depicts a first exemplary embodiment of a fuel supply system according to the invention, with a pressure-holding valve. A fuel tank  1 , the upper half of which is not shown in  FIG. 1 , has two low points  3 . A fuel reservoir  5  that is open at the top is disposed in the fuel tank  1 . 
   The internal combustion engine, not shown, and the associated fuel-supply pump feeds fuel from the fuel reservoir  5  to the engine by means of a fuel line  7  that extends into the fuel reservoir  5 . In order to prevent the fuel line  7  from emptying out, a first check valve  9  is provided at its end. 
   The purpose of the fuel reservoir  5  is to assure that the fuel line  7  aspirates fuel and not air for as long as possible, even when the level of fuel in the fuel tank  1  is low. The fuel reservoir  5  has a much smaller base than the base of the tank  1  and its wall is approximately the same height as the fuel tank  1 . This makes it possible to achieve a high fill level in the fuel reservoir  5  with a small quantity of fuel and to consequently assure that the fuel line  7  aspirates fuel for as long as possible. 
   The fuel reservoir  5  is filled by means which are essentially comprised of a fuel pump  11  and a jet pump  13  in each low point  3  of the fuel tank  1 . One of the jet pumps  13  feeds fuel into the lower region of the fuel reservoir  5  and has a second check valve  15 , which prevents fuel from flowing back out of the fuel reservoir  5  into the tank  1 . When the fuel pump  11  is switched off, the fuel reservoir  5  is filled by means of the check valve  15 , as a result of which the fill level in the fuel reservoir  5  is at least approximately the same as the fill level in the fuel tank  1 . The other jet pump  13  feeds over the upper rim of the fuel reservoir  5  so that no check valve is required in it. 
   The fuel tank  1  is fed by a fuel return  17 , which conveys excess fuel back to the fuel tank  1 . The fuel pump  11  aspirates fuel from the fuel reservoir  5  by means of a preliminary filter  19  and feeds it via supply lines  21  to the jet pumps  13  and via a connecting line  23  into the fuel line  7 . In order to assure the pressure required for the jet pumps  13 , the connecting line  23  is provided with an overflow valve  25 , which is designed so that it only opens when the required working pressure of the jet pumps  13  has been achieved. As soon as the overflow valve  25  opens, part of the fuel delivered by the fuel pump  11  is fed via the connecting line  23  into the fuel line  7 . The first check valve  9  in the fuel line  7  also prevents fuel from traveling out of the connecting line  23  and back into the fuel reservoir  5 . This arrangement assures that the fuel line  7  is filled with fuel in an extremely short time and consequently permits the engine to be started. 
     FIG. 7  shows a graph of the characteristic curve of this exemplary embodiment according to the invention. The pressure difference in bar is plotted on the abscissa  27 , while the ordinate  29  shows the flow rate in liters per hour. The characteristic curve of the first exemplary embodiment is labeled  31 . It shows that only after reaching a pressure difference of 0.3 bar does the overflow valve  25  open and the flow rate, beginning from zero, rises in a linear fashion with the increasing pressure difference. 
     FIG. 2  shows a second exemplary embodiment of a fuel supply system according to the invention, which in lieu of a pressure-holding valve, has a throttle  33  in the connecting line  23 . This produces a characteristic curve that differs from that of the first exemplary embodiment. The characteristic curves  35  and  37  for two different throttle cross sections are plotted in FIG.  7 . They show that even with a very slight pressure difference, fuel is already being fed into the connecting line  23  so that the fuel line  7  is filled rapidly. Under unfavorable conditions, the pressure that builds up on the pressure side of the fuel pump  11  can be insufficient to assure the function of the jet pumps  13 . 
   In order to prevent this, in an exemplary embodiment according to  FIG. 3 , a throttle  33  is combined with a third check valve  39 .  FIG. 7  shows the characteristic curve  41  of the check valve  39 . It shows that when a certain pressure difference is reached, approximately 0.16 bar here, the third check valve  39  opens and the flow rate rises very sharply with increasing pressure difference. The combination of the characteristic curves of the third check valve  39  and the throttle  33  is depicted in  FIG. 7  as the characteristic curve  43 . This curve shows that in this exemplary embodiment, a certain amount of pressure difference is built up first before the supply pump  11  feeds fuel into the fuel line  7 . This improves the operating conditions for the jet pumps  13  and also, the third check valve  39  assures that when the engine is not in use, no fuel flows out of the fuel line  7 , through the connecting line  23 , and back into the fuel reservoir  5 . This assures that the fuel line  7  cannot empty out when the engine is not in use. This also contributes to an improved starting behavior of the internal combustion engine. 
   It goes without saying that the characteristic curves  31 ,  35 ,  37 ,  41 , and  43  from  FIG. 7  are only intended as examples of a concrete combination of the fuel pump  11 , connecting line  23 , overflow valve  25 , throttle  33 , and/or check valve  39 . The quantitative course of the above-mentioned characteristic curves can be varied greatly by changing one or more of these components; the qualitative course of the characteristic curves, however, is retained. 
     FIGS. 4 ,  5 , and  6  show a fourth exemplary embodiment in different operating states. The fuel line  7  has a fuel filter  45  and a fuel delivery pump  47 . The fuel fed from the fuel reservoir  5  by the fuel pump  11  is controlled by means of a 3/3-port directional-control valve  49 , which is shown in a first switched position. The 3/3-port directional-control valve  49  has a first connection  51 , which connects the fuel pump  11  to the 3/3-port directional-control valve  49 . A second connection of the 3/3-port directional-control valve  49  is connected to the connecting line  23 , while the third connection is connected to the supply line  21 . 
   The 3/3-port directional-control valve has a piston  53 . This piston  53  has a connecting bore with a throttle  55 , which connects a first chamber  57  of the 3/3-port directional-control valve  49  to a second chamber  59 . A third chamber  61  contains a spring  63 , which always brings the 3/3-port directional-control valve into the first switched position shown in  FIG. 4  when the fuel pump  11  is inoperative. 
   As soon as the fuel pump  11  is activated, it feeds into the first chamber  57  of the 3/3-port directional-control valve. Since in this switched position, the connecting line  23  is connected to the first chamber  57 , the fuel pump  11  feeds into the fuel line  7 . A part of the flow stream of the fuel pump  11  travels through the connecting bore with the throttle  55  in the piston  53 , and into the second chamber  59 , causing the piston  53  to move toward the spring  63 , counter to the force of the spring  63 . 
     FIG. 5  shows the fourth exemplary embodiment in a second switched position. The piston  53  is positioned so that the chamber  57  is hydraulically connected to both the connecting line  23  and the supply line  21 . In this position, the fuel pump  11  supplies fuel to both the fuel line  7  and the jet pumps  13 . 
     FIG. 6  shows the third switched position of the 3/3-port directional-control valve. In this switched position, the fuel pump  11  only feeds into the supply line  21  and not into the connecting line  23 . This means that the entire output of the fuel pump  11  is fed to the jet pumps  13 . 
     FIG. 6  A shows a modification in which a 3/2-port directional-control valve is used in place of the 3/3-port directional-control valve. In this embodiment, the line  23  is closed before the line  21  is opened so that the pump feeds only to line  21 . 
   In this fourth exemplary embodiment, the fuel line  7  is filled as rapidly as possible and at the same time, the jet pumps  13  are driven as soon as possible. As a result, this produces a very favorable starting behavior of the engine, not shown, and it is possible for the fuel pump  11  to be small since it only has to continuously operate to supply the jet pumps  13 . Optionally, a throttle  65  can be provided in the connecting line  23 , which results in the fact that the fuel flow in the connecting line  23  is reduced and consequently, a greater portion of the fuel flow delivered by the fuel pump  11  flows through the connecting bore  55  into the second chamber  59 . This increases the speed with which the piston  53  moves from the first switched position into the third. 
   All of features shown in the drawings, the specifications, and the claims can be essential to the invention either individually or in arbitrary combinations with one another.
The invention proposes a fuel supply system for internal combustion engines, having a fuel tank ( 1) and a fuel reservoir ( 5) disposed therein, having a fuel pump ( 11), which drives one or more jet pumps ( 13), each by means of a supply line ( 21), the jet pumps ( 13) in turn filling the fuel reservoir ( 5) with fuel from the fuel tank ( 1). There is also a fuel line ( 7), which hydraulically connects the fuel reservoir ( 5) to the engine. During the starting of the engine, the fuel pump ( 11) feeds fuel into the fuel line ( 7), thus improving the starting behavior of the engine.