Patent Publication Number: US-7219654-B2

Title: Fuel injection device for an internal combustion engine

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a 35 USC 371 application of PCT/DE 2004/001690 filed on Jul. 28, 2004. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention is directed to an improved fuel injection system for an internal combustion engine. 
   2. Description of the Prior Art 
   A fuel injection system of the type with which this invention is cornered, known from DE 100 02 132 A1, has a high-pressure pump that delivers fuel to an accumulator. A fuel supply pump delivers fuel from a fuel tank to the suction side of the high-pressure pump, and a fuel metering unit between the fuel supply pump and the high-pressure pump can variably adjust the quantity of fuel taken in by the high-pressure pump. The accumulator is connected to at least one injector that injects fuel into the internal combustion engine. A fuel return leads from the injector back to the fuel tank. In order to assure that the high-pressure pump delivers a sufficient supply of fuel to the accumulator in all operating states of the engine, the fuel supply pump must deliver a sufficiently large quantity of fuel to the high-pressure pump. But in order to achieve this, it becomes necessary to provide a fuel supply pump with very large dimensions, which increases the weight and amount of space required of the fuel injection system and also contributes to high manufacturing costs. 
   SUMMARY AND ADVANTAGES OF THE INVENTION 
   The fuel injection system according to the present invention has the advantage over the prior art that the fuel supply pump can be of relatively small dimensions, which makes it possible to minimize the space required, weight, and costs of the fuel injection system. Only when the quantity of fuel delivered by the fuel supply pump is less than the required intake quantity of the high-pressure pump does the high-pressure pump also take in additional fuel from the fuel return. This assures that the high-pressure pump takes in predominantly the cool fuel delivered by the fuel supply pump and only the shortfall is made up by the heated fuel from the fuel return. 
   Advantageous embodiments and modifications of the fuel injection system according to the present invention are disclosed. One embodiment assures that the high-pressure pump will only take in fuel from the fuel return if the fuel quantity delivered by the fuel supply pump falls short of the required intake quantity. Another embodiment provides for a lubrication and cooling of the drive region of the high-pressure pump while still another assures that the drive region of the high-pressure pump is supplied exclusively with fuel delivered by the fuel supply pump, i.e. cooler fuel. In a further embodiment only the fuel quantity taken in by the high-pressure pump passes through the filter, thus allowing a smaller or simpler filter design to be used. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A number of exemplary embodiments of the present invention are explained in greater detail in the subsequent description, taken in conjunction with the drawings, in which: 
       FIG. 1  is a schematic depiction of a first exemplary embodiment of a fuel injection system for an internal combustion engine according to the invention, 
       FIG. 2  shows the fuel injection system according to a second exemplary embodiment, and 
       FIG. 3  shows the fuel injection system according to a third exemplary embodiment. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1 to 3  show a fuel injection system for an internal combustion engine, for example of a motor vehicle. The engine is an autoignition internal combustion engine, for example, and has one or more cylinders. The motor vehicle has a fuel tank  10  that stores fuel for the operation of the engine. The fuel injection system has a fuel supply pump  12  that delivers fuel from the fuel tank  10  to a high-pressure pump  14 . The high-pressure pump  14  delivers fuel to an accumulator  16  that can be embodied, for example, in the form of a tube or in any other shape. At least one line  18  leads from the accumulator  16  to at least one injector  20  associated with a cylinder of the engine; preferably, the accumulator  16  is connected to a number of injectors  20 . Each of the injectors  20  is provided with an electric control valve  22  that controls at least one opening of the respective injector in order to trigger or prevent a fuel injection through the injector  20 . An electronic control unit  23  triggers the control valves  22  and, as a function of operating parameters of the engine such as engine speed, load, temperature, etc., determines the time and duration of the fuel injection through the injectors  20 . A fuel return for unused fuel leads back from the injectors  20 , for example via a line  24  that is shared by all of the injectors  20 . A line  26  functioning as a return can also lead from the accumulator  16  back to the fuel tank  10 , which line contains a pressure-limiting valve or pressure control valve  28  that prevents an impermissibly high pressure from building up in the accumulator  16  and can vary the pressure prevailing in the accumulator  16 . Between the accumulator  16  and the injectors  20 , a pressure boosting device  21  can be provided, which further increases the pressure available for fuel injection in comparison to the pressure prevailing in the accumulator  16 . The pressure boosting device  21  is preferably integrated into the injector  20  and is embodied in the form of a hydraulic pressure booster. In this case, the fuel return  24  preferably leads from the pressure booster  21  of the injectors  20 . 
   The high-pressure pump  14  is mechanically driven by the internal combustion engine and is therefore driven in proportion to the speed of the engine. In a first exemplary embodiment shown in  FIG. 1 , the fuel supply pump  12  is likewise mechanically driven by the engine or the high-pressure pump  14 . In this case, the fuel supply pump  12  is preferably mounted onto the high-pressure pump  14  or integrated into it. A filter  30  is provided between the fuel supply pump  12  and the fuel tank  10 . In addition, a throttle restriction  31  can be provided in the connection between the fuel supply pump  12  and the fuel tank  10  in order to limit the flow. The fuel tank  10  can contain a collecting reservoir  32  from which the fuel supply pump  12  draws fuel and into which a jet pump  33  delivers fuel from the fuel tank  10 . The motive flow of the jet pump  33  is supplied to it from the accumulator  16  via the fuel return  26 . 
   The high-pressure pump  14  can be embodied in the form of a radial piston pump and has at least one and possibly several pump elements, each of which has a pump piston that delimits a pump working chamber and is driven into a reciprocating motion by drive shaft. A fuel metering unit  36  is provided between the fuel supply pump  12  and the high-pressure pump  14 . The fuel metering unit  36  has a control valve  38  that is actuated, for example, by an electric actuator  37 , preferably an electromagnet or a piezoelectric actuator, and can continuously adjust the flow from the fuel supply pump  12  to the high-pressure pump  14 . The control valve  38  can be embodied in the form of a proportional valve that can continuously change the flow cross section between the fuel supply pump  12  and high-pressure pump  14 . Alternatively, the control valve  38  can also be opened and closed cyclically, which makes it possible to change an average effective flow cross section between the fuel supply pump  12  and the high-pressure pump  14 . The fuel metering unit  36  is preferably mounted onto the high-pressure pump  14  or integrated into it, but can also be disposed separate from the high-pressure pump  14 . The control unit  23  triggers the fuel metering unit  36  in such a way that the fuel supply pump  12  delivers a fuel quantity to the high-pressure pump  14  that the high-pressure pump  14  then in turn delivers at high pressure to the accumulator  16  in order to maintain a predetermined pressure in the accumulator  16  as a function of operating parameters of the internal combustion engine. The accumulator  16  is associated with a pressure sensor in the pressure control valve that is connected to the control unit  23  and supplies it with a signal indicating the current pressure in the accumulator  16 . 
   The fuel return  24  from the injectors  20  feeds into the connection between the fuel supply pump  12  and the fuel metering unit  36 . A connection  40  controlled by a pressure valve  42  leads from the fuel return  24  to a discharge region that can be comprised, for example, of the fuel tank  10 . The pressure valve  42  opens the connection  40  when a predetermined pressure is exceeded so that fuel can flow out into the fuel tank  10 . The connection  40  can feed into the return line  26  from the accumulator  16  so that the fuel quantity diverted via the pressure valve  42  is also supplied to the jet pump  33  as a motive flow. The pressure valve  42  is preferably mounted onto the high-pressure pump  14  or integrated into it. The connection  40  branches off from the fuel return  24  spaced apart from its outlet into the connection between the fuel supply pump  12  and the fuel metering unit  36 , thus yielding a fuel return segment  24   a  that extends between the outlet and the branching-off point of the connection  40 . 
   From the connection between the fuel supply pump  12  and the fuel metering unit  36 , in a region between the fuel supply pump  12  and the outlet of the fuel return segment  24   a , a bypass connection  44  branches off to a drive region of the high-pressure pump  14 . The drive region of the high-pressure pump  14  referred to here includes its drive shaft as well as the region in which the rotary motion of the drive shaft is converted into the reciprocating motion of the pump pistons. The fuel flowing via the bypass line  44  into the drive region assures a lubrication and cooling of the drive region. The bypass connection  44  preferably contains a throttle restriction  45  to limit the fuel quantity supplied to the drive region. A return  46  leads from the drive region of the high-pressure pump  14  back to the fuel tank  10  and can feed, for example, into the connection  40  and the return  26  from the accumulator  16 . The return  46  assures a constant flow through the drive region of the high-pressure pump  14 . 
   The function of the fuel injection system according to the first exemplary embodiment will be explained below. During operation of the internal combustion engine, the fuel supply pump  12  draws fuel from the fuel tank  10  and delivers it via the fuel metering unit  36  to the suction side of the high-pressure pump  14 . The high-pressure pump  14  delivers fuel at high pressure to the accumulator  16 . The injectors  20  inject fuel into the cylinders of the engine and the control unit  23  determines the timing of the fuel injection and the quantity of injected fuel by triggering the control valves  22  as a function of operating parameters of the engine. The control unit  23  also triggers the fuel metering unit  36  so that it sets a flow cross section great enough that the high-pressure pump  14  draws and delivers to the accumulator  16  the fuel quantity required to maintain a predetermined pressure in the accumulator  16 . 
   Particularly if the injectors  20  are provided with pressure boosters  21 , depending on the operating state of the engine, the high-pressure pump  14  must deliver a large quantity of fuel to the accumulator  16  and the fuel supply pump  12  must deliver this large quantity of fuel from the fuel tank  10  to the high-pressure pump  14 . This can require that the fuel supply pump  12  be designed with very large dimensions. According to the present invention, however, the fuel supply pump  12  is dimensioned so that the maximum quantity of fuel it can deliver is less than the maximum quantity of fuel that the high-pressure pump  14  must take in and deliver to the accumulator  16 . In operating states in which the quantity of fuel that the fuel supply pump  12  delivers from the fuel tank  10  is insufficient, the high-pressure pump  14  takes in part of the fuel quantity flowing from the injectors  20  through the fuel return  24  in addition to the quantity of fuel delivered by the fuel supply pump  12 . In the process of this, part of the fuel flowing through the fuel return  24  flows out through the fuel return segment  24   a  into the connection between the fuel supply pump  12  and the fuel metering unit  36  and is taken in by the high-pressure pump  14 . The remaining part of the quantity of fuel flowing through the fuel return  24  flows through the open pressure valve  42 , via the connection  40 , and into the fuel tank  10 . The quantity of fuel flowing into the drive region via the bypass line  44  is thus exclusively drawn from the quantity of fuel that the fuel supply pump  12  delivers from the fuel tank  10  and is therefore relatively cool. The fuel quantity taken in by the high-pressure pump  14  is likewise relatively cool since only part of this fuel quantity is drawn from the heated fuel return  24 . 
   In operating states in which the fuel quantity that the fuel supply pump  12  delivers from the fuel tank  10  is sufficient to supply the required intake quantity of the high-pressure pump  14 , the high-pressure pump  14  only takes in fuel delivered by the fuel supply pump  12  and the entire quantity of fuel flowing through the fuel return  24  is conveyed through the open pressure valve  42 , via the connection  40 , and into the fuel tank  10 . In operating states in which the fuel supply pump  12  delivers a quantity of fuel greater than the required intake quantity of the high-pressure pump  14 , part of the fuel quantity delivered by the fuel supply pump  12  is conveyed back through the fuel return segment  24   a  and through the open pressure valve  42 , via the connection  40 , and likewise into the fuel tank  10 . In these operating states, the high-pressure pump  14  consequently only takes in the relatively cool fuel quantity delivered by the fuel supply pump  12 . 
   The fuel flows through the fuel return segment  24   a  in different directions depending on the operating state. If the quantity of fuel delivered by the fuel supply pump  12  is less than the required intake quantity of the high-pressure pump  14 , then a partial quantity of the fuel quantity flowing back from the injectors  20  through the fuel return  24  flows through the fuel return segment  24   a  in the direction toward the high-pressure pump  14 . If the quantity of fuel delivered by the fuel supply pump  12  is greater than the required intake quantity of the high-pressure pump  14 , then a partial quantity of the fuel quantity delivered by the fuel supply pump  12  flows through the fuel return segment  24   a  in the direction toward the pressure valve  42 . The fuel return segment  24   a  thus assures that when the delivery quantity of the fuel supply pump  12  is sufficient, the high-pressure pump  14  only takes in fuel delivered by the fuel supply pump  12  and only when the delivery quantity of the fuel supply pump  12  is insufficient, does the high-pressure pump  14  also take in fuel from the fuel return  24 . Only the fuel quantity delivered by the fuel supply pump  12  flows through the filter  30 , whereas the fuel quantity drawn from the fuel return  24  is not introduced until after the filter  30 . But the excess fuel potentially delivered by the fuel supply pump  12  and diverted via the fuel return segment  24   a , the pressure valve  42 , and the connection  40  also flows through the filter  30 . 
     FIG. 2  shows the fuel injection system according to a second exemplary embodiment in which the fundamental design is the same as in the first exemplary embodiment and only the fuel supply pump  12  has been modified. The fuel supply pump  12  is disposed separate from the high-pressure pump  14 , has an electric drive unit, and is preferably disposed inside the fuel tank  10 . The filter  30  is provided between the fuel supply pump  12  and the fuel metering unit  36 ; the bypass connection  44  to the drive region of the high-pressure pump  14  branches off between the filter  30  and the fuel metering unit  36 . Inside the fuel tank  10 , a return  48  that leads back into the fuel tank  10  and is controlled by a pressure valve  49  branches off from the connection of the fuel supply pump  12  to the filter  30 . The pressure valve  49  and the return  48  limit the pressure between the fuel supply pump  12  and the filter  30 , thus preventing an impermissible increase in pressure if the filter  30  becomes clogged, for example. The remainder of the design and function of the fuel injection system according to the second exemplary embodiment is the same as in the first exemplary embodiment described above. 
     FIG. 3  shows the fuel injection system according to a third exemplary embodiment in which the fundamental design is the same as in the second exemplary embodiment, but the disposition of the pressure valve  42  and the fuel return segment  24   a  has been modified. The fuel supply pump  12  has an electric drive unit and is disposed in the fuel tank  10 . The bypass connection  44  leading to the drive region of the high-pressure pump  14  branches off between the filter  30  and fuel metering unit  36 . The fuel return  24  from the injectors  20  feeds into the connection between the fuel supply pump  12  and the filter  30 . The connection  40  controlled by the pressure valve  42  leads from the fuel return  24  to the fuel tank  10 . The fuel return segment  24   a  is disposed between the branch-off point of the connection  40  and the outlet of the fuel return  24  into the connection between the fuel supply pump  12  and the filter  30 . In the third exemplary embodiment, the pressure valve  42  can be disposed separate from the high-pressure pump  14 . 
   The function of the fuel injection system according to the third exemplary embodiment is essentially the same as in the first and second exemplary embodiments. Fuel flows through the fuel return segment  24   a  in different directions depending on the operating state. If the fuel quantity delivered by the fuel supply pump  12  is less than the required intake quantity of the high-pressure pump  14 , then a partial quantity of the fuel quantity flowing from the injectors  20  through the fuel return  24  flows through the fuel return segment  24   a  in the direction toward the high-pressure pump  14 . If the fuel quantity delivered by the fuel supply pump  12  is greater than the required intake quantity of the high-pressure pump  14 , then a partial quantity of the fuel quantity delivered by the fuel supply pump  12  flows through the fuel return segment  24   a  in the direction toward the pressure valve  42 . The fuel return segment  24   a  thus assuring that if the delivery quantity of the fuel supply pump  12  is sufficient, then the high-pressure pump  14  exclusively takes in fuel delivered by the fuel supply pump  12  and only if the delivery quantity of the fuel supply pump  12  is insufficient, does the high-pressure pump  14  also take in fuel from the fuel return  24 . By contrast with the first and second exemplary embodiments, in the third exemplary embodiment, the entire quantity of fuel taken in by the high-pressure pump  14  flows through the filter  30 . The excess fuel potentially delivered by the fuel supply pump  12 , however, does not flow through the filter  30  because it is diverted via the fuel return segment  24   a , the pressure valve  42 , and the connection  40  before reaching the filter  30 . Only with a sufficient delivery quantity of the fuel supply pump  12  is the fuel quantity delivered to the drive region of the high-pressure pump  14  via the bypass connection  44  diverted exclusively from the cold fuel supply that the fuel supply pump  12  delivers from the fuel tank  10 . When the delivery quantity of the fuel supply pump  12  is insufficient, the fuel quantity delivered to the drive region is drawn from the mixture of the cold fuel that the fuel supply pump  12  delivers from the fuel tank  10  and the heated fuel taken from the fuel return  24 . By contrast with the first and second exemplary embodiments, in the third exemplary embodiment, when the delivery quantity of the fuel supply pump  12  is insufficient, the drive region of the high-pressure pump  14  is consequently supplied with fuel at a slightly higher temperature. 
   The foregoing relates to preferred exemplary embodiments of the invention, it being understood that other variants and embodiments thereof are possible wherein the spirit and scope of the invention, the latter being defined by the appended claims.