Abstract:
A fuel supply device for an internal combustion engine has a supply container, at least one feed pump for supplying a fuel from the supply container, a high pressure pump to which the fuel is supplied from the supply container by the feed pump, so that the fuel is supplied under high pressure at least indirectly to injection points of an internal combustion engine, the feed pump being driven mechanically by the internal combustion engine, and a further feed pump provided additionally to the mechanically driven feed pump and supplying the fuel from the supply container to the high pressure pump, the further feed pump having an electric drive and being operable independently from the mechanically driven feed pump.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a fuel supply device for an internal combustion engine. 
     Fuel supply devices of this type are disclosed for example in the publication “Dieselmotor Management”, Verlag Vieweg, 2 edition 1999, pages 262-263. The fuel supply device has a feed pump which supplies the fuel from a supply container to a high pressure pump. With the high pressure pump, the fuel is supplied under high pressure at least indirectly to injection points on the internal combustion engine. The feed pump is driven mechanically by the internal combustion engine. During start of the internal combustion engine the feed pump is driven with a low rotary speed, so that the fuel quantity supplied by it in this condition is not sufficient to provide a reliable start of the internal combustion engine. In particular, at high fuel temperatures and low rotary speeds of the internal combustion engine, for example because of a not sufficient voltage of the board current source, the feed pump does not supply sufficient fuel quantity. The feed pump can be modified so that it supplies a greater fuel quantity, but in other operational conditions then the required fuel quantity will be too high and must be uselessly withdrawn. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a fuel supply device for an internal combustion engine, which avoids the disadvantages of the prior art. 
     In keeping with these objects and with others which will become apparent hereinafter, one feature of present invention resides, briefly stated, in a fuel supply device for an internal combustion engine which has a supply container, at least one feed pump for supplying a fuel from the supply container, a high pressure pump to which the fuel is supplied from the supply container by the feed pump, so that the fuel is supplied under high pressure at least indirectly to injection points of an internal combustion engine, the feed pump being driven mechanically by the internal combustion engine, and a further feed pump provided additionally to the mechanically driven feed pump and supplying the fuel from the supply container to the high pressure pump, the further feed pump having an electric drive and being operable independently from the mechanically driven feed pump. 
     When the fuel supply device is designed in accordance with the present invention, it has the advantage that by the electrically driven further feed pump, intentionally in the required operational conditions the fuel quantity supply by the high pressure pump is increased, so that a reliable start and a reliable operation of the internal combustion engine is guaranteed in all operational conditions. 
     In accordance with another feature of present invention, the mechanically driven feed pump and the further feed pump are assembled to form a feed module. Therefore a simple construction is provided. 
     In accordance with a further feature of present invention, the feed module has a suction connection to the supply container, through which both feed pumps aspirate fuel, a pressure connection to the high pressure pump through which both feed pumps supply fuel, and a check valve arranged between the pressure connection and the further feed pump and closing toward the further feed pump. With this construction a return flow of the fuel, which is supplied by the mechanically driven feed pump through the further feed pump into the supply container, is reliably prevented. 
     In accordance with another feature of present invention, the further feed pump is operated in the event of a failure of the mechanically driven feed pump. Therefore it is guaranteed that the internal combustion engine at least in an emergency situation can operate in the case of a failure of the mechanically driven feed pump. 
     Finally, in accordance with another feature of present invention, the further feed pump supplies a smaller fuel quantity than the maximum fuel quantity of the mechanically driven feed pump. Therefore a simple and cost favorable construction of both feed pumps can be provided. 
     The novel features which are considered as characteristic for the present invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a view showing a fuel supply device for an internal combustion engine in a schematic illustration; 
     FIG. 2 is a view showing a feed module of the fuel supply device, on an enlarged scale; and 
     FIG. 3 is a view showing a characteristic field of the fuel quantity supplied by the feed pumps of the feed module, depending on a rotary speed. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a fuel supply device for an internal combustion engine  10  of a motor vehicle or a stationary internal combustion engine, which is a self-igniting internal combustion engine. 
     The fuel supply device has a feed pump  12  which supplies the fuel from a supply container  14 . The feed pump  12  can be formed as a gear pump and can be driven mechanically by the internal combustion engine  10 . The rotary speed of the feed pump  12  is proportional to the rotary speed of the internal combustion engine  10 . Downstream after the feed pump  12 , a high pressure pump  16  is arranged. Its suction side supplies the fuel which is displaced by the feed pump  12 . High pressure storage  18  is arranged downstream of the high pressure pump  16 . 
     Conduits  20  from the pressure storage  18  lead to injection points  22  at the cylinders of the internal combustion engine  10 . Injectors are arranged at the injection points  22  and inject fuel into the combustion chambers of the cylinders of the internal combustion engine  10 . Valves  21  are provided for controlling the injection of the injectors. They establish the connection of the injectors with the high pressure storage  8  or interrupt the connection. Alternatively, it can be provided that for each cylinder of the internal combustion engine  10 , a high pressure pump is provided. Its suction side is connected with the feed pump  12 . 
     In accordance with the present invention, in addition to the mechanically driven feed pump  12 , a further feed pump  30  is provided. It has an electrical drive  32 . The drive  32  is formed for example by a direct current electric motor, and the board current source of the motor vehicle serves as a current source. With the further feed pump  30 , during its operation parallel to the mechanically driven feed pump  12 , fuel is fed from the supply container  14  and supplied to the high pressure pump  16 . The mechanically driven feed pump  12  and the further feed pump  30  are assembled for example to form a feed module  34 . The feed module  34  is shown in FIG. 2 on an enlarged scale. 
     The feed module  34  has a housing  36  with a suction-side connection  38 . A suction conduit  39  to the supply container  14  is connected to the connection  38 . A pressure-side connection  40  is arranged moreover on the housing  36 . A pressure conduit  41  for the high pressure pump  16  is connected to the connection  40 . A pump chamber  42  is limited in the housing  36  for the feed pump  12 . Two toothed gears  44  which engage with one another over their outer periphery are arranged as components of the feed pump  12  in the pump chamber  42 . One of the toothed gears  44  is driven in a not shown manner by the internal combustion engine  10 . During the operation of the feed pump  12  fuel is supplied by its rotatable toothed gears  44  along supply passages  46  which extend over their periphery, from the suction side with the suction connection  38  to the pressure side with the pressure connection  40 . 
     The further feed pump  40  is formed for example as a diaphragm pump and has a diaphragm  50  arranged in the housing  36  in a further pump chamber  48 . The diaphragm  50  is connected with a plunger  52  which is driven by the electric motor  32  in a stroke movement. The electric motor  32  can be arranged in the housing  36  or, as shown in FIG. 2, outside of the housing  36 . A shaft  54  of the electric motor  32  extends in the housing  36  and is coupled with the plunger  52  by an eccentric  55 , so that during rotary movement of the shaft  54  the plunger  52  is driven in the stroke movement. The stroke movement of the plunger  52  is transmitted to the diaphragm  50 . A pump working chamber  56  is limited by the diaphragm  50  in the pump chamber  48 . It communicates with the suction connection  38  through the connection  57  extending in the housing  36  for example in form of an opening or a channel. A check valve  58  which opens into the pump working chamber  56  is arranged in the connection  57  and opens during a suction stroke of the diaphragm  50 , so that fuel can be supplied from the suction connection  38  into the pump work chamber  56 . 
     The pump work chamber  56  is also connected with the pressure connection  40  through a connection  60  which extends in the housing  36 , and can be also formed as an opening or a passage. A check valve  61  which opens toward the pressure connection  40  is arranged in the connection  60 . During the forward stroke of the diaphragm  50  the check valve  58  closes and the check valve  61  opens, so that fuel is displaced from the pump work  56  to the pressure connection  40 . The check valve  61  is preferably arranged in the connection  60  near the pump work chamber  56 . The plunger  52 , the diaphragm  50  as well as the check valves  58  and  61  together with a housing part which receives these elements, can form a structural unit which is insertable into the housing  36  of the feed module  34 . A further check valve  62  can be arranged in the connection  60  of the pump work chamber  56  with the pressure connection  40  near the pressure connection  40 , so as to open toward the pressure connection  40  and to close toward the pump work chamber  56 . The check valve  62  prevents that the fuel supplied by the feed pump  12  can be displaced by the connection  60  in the pump work chamber  56  to the further feed pump  30 . 
     The operation on the further feed pump  30  is controlled for example by an electronic control device  70 , by which for example also the injection of the fuel with the injectors is controlled. The control device  70  supplies signals about the operational condition of the internal combustion engine  10 , in particular its rotary speed, load, cooling medium temperature, fuel temperature and in some cases further parameters. With the control device  70  the further feed pump  30 , is set in operation, in particular at low rotary speed and or at high cooling medium and/or fuel temperature. A low rotary speed of the internal combustion engine  10  occurs for example during starts, so that the further feed pump  30  is driven by the control device  70  during starts of the internal combustion engine  10  when the feed pump  12 , because of the low rotary speed of the internal combustion  10 , is also driven with a low rotary speed. 
     It can be provided that the further feed pump  30  is set in operation by the control device  70  before the start of the internal combustion engine  10 , so that the high pressure pump  16  is supplied with fuel prematurely. Thereby a good lubrication of the high pressure pump  16  is provided. It can be for example provided that the control device  70  supplies a signal about closing of the doors of the motor vehicle, or about the insertion of the ignition key into the ignition lock, or about the rotation of the ignition key in an ignition position, or a seat occupation recognition, and in this case sets the further feed pump  30  in operation. When the internal combustion engine  10  reaches a sufficiently high rotary speed, for example the orderly idle running rotary speed, then the control device  70  switches off the further feed pump  10  so that when only the feed pump  12  supplies fuel to the high pressure pump  16 . 
     It can be also provided that in the case of a failure of the feed pump  12 , when the internal combustion engine  10  can no longer be operated, the control device  70  sets the further feed pump  30  in operation. Thereby a sufficient fuel quantity is supplied to the high pressure pump  16 , in order to provide at least an emergency operation of the internal combustion engine  10  with a low power. Moreover, it can be provided that the further feed pump  30  is set in operation after the supply container  14  is completely emptied and is subsequently again filled. Thereby a ventilation and filling of the conduits  39  and  41  of the high pressure pump  16  is provided, so that during a subsequent start of the internal combustion engine  10  they are filled with fuel and the starting process can be shortened. 
     FIG. 3 shows a characteristic field of a fuel supply quantity over the rotary speed of the feed pump  12 , wherein the numerical values are only exemplary. The high pressure pump  16  at a fuel temperature of approximately −20° C. has a fuel consumption marked with the point A, and at the fuel temperature of approximately +90° C. has the fuel consumption marked with the point B. In FIG. 3 a characteristic line of the feed pump  12 , or in other words the feed quantity V′ over the pump rotary speed np, at the fuel temperature of approximately −20° C. is plotted and identified with C. A further characteristic line for a fuel temperature of approximately +90° C. is plotted and identified with D. It can be seen from FIG. 3 that the fuel supply by the fuel pump  12  is first started from a predetermined minimum rotary speed np min of the fuel pump  12  and increases with increasing fuel temperature. With increasing rotary speed np the fuel pump  12  increases the fuel quantity V′. In FIG. 3 moreover a characteristic line of the further feed pump  30  is plotted, which is identified with E. The characteristic line E of the further fuel pump  30  extends approximately horizontally since the further feed pump  30  is driven with a constant rotary speed and not as the feed pump  12  with a rotary speed which is proportional to the rotary speed of the internal combustion engine  10 . When the feed pump  12  reaches such a high rotary speed np 1 that by it a sufficiently great fuel quantity V′ is supplied, the further feed pump  30  is switched off. 
     The fuel quantity supplied by the further feed pump  30  is substantially smaller than the maximum fuel quantity supplied by the feed pump  12 . The supply quantity of the further fuel pump  30  can amount to, for example, approximately between 3% and 20% of the maximum supply quantity of the feed pump  12 . The further feed pump  30  is operated correspondingly only for a short time period, so that it suffices to design it for a relatively short service life, which makes possible a cost-favorable manufacture. With the use of the further feed pump  30 , the feed pump  12  can be produced in a simple manner, since high manufacturing tolerances can be accepted for it. Such high manufacturing tolerances, in particular at low pump rotary speeds worsen the supply power, which however is compensated by the supply power of the further feed pump  30 . The further feed pump  30  can be formed also as a separate unit with respect to the feed pump  12 . Moreover, the further feed pump  30  can be arranged before the feed pump  12  and connected in series to the supply container  14 . 
     It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of constructions differing from the types described above. 
     While the invention has been illustrated and described as embodied in fuel supply device for an internal combustion engine, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention. 
     Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention. 
     What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims.