Abstract:
The fuel injection device for an internal combustion engine comprises a feed pump which has an electric drive, by which feed pump fuel is fed from a fuel storage tank into a low-pressure region to the suction side of at least one high-pressure pump. The high-pressure pump pumps fuel into a high-pressure region in which at least one injector is provided to inject the fuel into the internal combustion engine. The fuel injection is controlled by an electric control device. Arranged in the low-pressure region is a pressure sensor which is connected to the control device. The electric drive of the feed pump is activated by the control device in order to set a feed quantity of the feed pump which is variable as a function of at least one operating parameter of the internal combustion engine and/or of the high-pressure pump. The drive of the feed pump is in particular activated by the control device in such a way that, at a high load of the internal combustion engine and/or at a high rotational speed and/or at a high fuel temperature, a greater fuel quantity is fed by the feed pump into the low-pressure region than at a low load and/or a low rotational speed and/or a low fuel temperature.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a 35 USC 371 application of PCT/EP 2007/054067 filed on Apr. 25, 2007. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention is based on a fuel injection device for an internal combustion. 
     2. Description of the Prior Art 
     A fuel injection device of this kind is known from DE 103 43 482 A1. This fuel injection device has a delivery pump, which is equipped with an electric drive unit and delivers fuel from a fuel tank to the intake side of a high-pressure pump. The high-pressure pump delivers fuel into a high-pressure region; in the high-pressure region, at least one injector is provided, which is situated on the internal combustion engine and injects fuel into the engine. The fuel injection device also has an electronic control unit that controls the fuel injection as a function of operating parameters of the internal combustion engine. Between the delivery pump and the intake side of the high-pressure pump, a fuel metering device is provided, which is triggered by the electronic control unit and is able to vary the fuel supply to the intake side of the high-pressure pump and therefore the fuel quantity that the high-pressure pump delivers into the high-pressure region. In the high-pressure region, a pressure sensor is provided, which is connected to the electronic control unit and detects the pressure in the high-pressure region; the control unit triggers the fuel metering device so that the high-pressure pump supplies the high-pressure region with the fuel quantity that is required to maintain a predetermined pressure in the high-pressure region. The delivery pump is operated at an essentially constant speed so that it delivers an essentially constant fuel quantity that must be dimensioned so that the maximum fuel demand of the internal combustion engine is made available. As a result, the delivery quantity of the delivery pump is too large in most operating states of the engine other than full load. The excess fuel quantity of the fuel pump is diverted into a pressure-relief region by an overflow valve situated between the delivery pump and the fuel metering device. The delivery pump in this case must be very large and must be dimensioned for a corresponding long-term load, which results in high manufacturing costs and a high electrical power demand for its operation. 
     ADVANTAGES AND SUMMARY OF THE INVENTION 
     The fuel injection device according to the invention, with the defining characteristics recited in claim  1 , has the advantage over the prior art that the delivery pump is operated in a demand-controlled fashion making it possible, in terms of its dimensioning, for it to be designed for a lower average long-term load and the electric power demand for its drive unit to be significantly lower, averaged out over all operating states of the internal combustion engine. In this case, the operation of the delivery pump can be optimized, for example, to improve the operating conditions of the high-pressure pump. 
     Advantageous embodiments and modifications of the fuel injection device according to the invention are disclosed in additional to the above. The invention has the advantage that a possible pressure drop during the passage through the fuel filter has no influence on the pressure detection in the low-pressure region. The invention further has the advantage of an improvement in the lubrication and/or cooling of the drive region of the high-pressure pump under a high load. The invention further has the advantage of an improvement in the lubrication and/or cooling of the drive region of the high-pressure pump at high fuel temperatures. The invention further has the advantage that fuel delivered by the delivery pump that is not taken in by the high-pressure pump can be diverted out of the low-pressure region. The invention further has the advantage that the total fuel quantity delivered by the delivery pump is available for lubrication and/or cooling of the drive region of the high-pressure pump. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the invention are shown in the drawings and described in further detail in the ensuing description, in which: 
         FIG. 1  is a schematic depiction of a fuel injection device for an internal combustion engine according to a first exemplary embodiment, 
         FIG. 2  is a graph in which the delivery quantity of a delivery pump and the overflow quantity of an overflow valve are plotted over the pressure prevailing in a low-pressure region, and 
         FIG. 3  is a schematic depiction of the fuel injection device according to a second exemplary embodiment. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIGS. 1 and 3  schematically depict a fuel injection device for an internal combustion engine, for example of a motor vehicle. The fuel injection device has a delivery pump  10  that draws fuel from a fuel tank  12 . The delivery pump  10  has an electric drive unit  14  in the form of an electric motor and the delivery pump  10  can be situated outside the fuel tank  12  or, as depicted in  FIGS. 1 and 3 , inside the fuel tank  12 . Inside the fuel tank  12 , a fuel collecting cup or swirl pot  16  can be provided, from which the delivery pump  10  draws fuel and which assures that the delivery pump  10  is able to draw fuel even when the fuel level in the fuel tank  12  is low. For example, fuel is delivered into the swirling pot  16  by means of at least one jet pump  18 . The delivery pump  10  delivers fuel to the intake side of a high-pressure pump  20  of the fuel injection device. Between the delivery pump  10  and the intake side of the high-pressure pump  20 , a fuel filter  22  is provided, which purifies the fuel delivered by the delivery pump  10  before it flows to the high-pressure pump  20 . 
     The high-pressure pump  20  has one or more pump elements  24 , each of which is equipped with a respective pump piston  28  guided in a cylinder bore  26 . Each pump piston  28  delimits a pump working chamber  30  in the respective cylinder bore  26 . The respective pump pistons  28  are each set into a stroke motion at least indirectly by a drive shaft  32  that is driven to rotate by the internal combustion engine. The drive shaft  32  is supported in rotary fashion for example by means of two bearing points situated spaced apart from each other in the direction of the rotation axis of the drive shaft  32  in a housing  34  of the high-pressure pump  14 . The bearing points can be situated in various parts of the pump housing  34 ; for example a first bearing point can be situated in a base body of the pump housing  34  and a second bearing point can be situated in a flange component attached to the base body. In a region situated between the two bearing points, the drive shaft  32  has at least one cam  36  or a section situated eccentric to its rotation axis; the cam  36  can also be embodied in the form of a multilobe cam. The drive shaft  32  of the high-pressure pump  20  is driven by the internal combustion engine, for example by means of its crankshaft or camshaft. The drive shaft  32  can be coupled to the engine, for example, by means of a belt (toothed belt), a chain, or gears. Because the high-pressure pump  20  is driven by the engine, the speed of the drive shaft  32  of the high-pressure pump  20  is proportional to the speed of the engine. 
     Each of the pump pistons  28  can rest against the cam  36  or eccentric of the drive shaft  32  directly or indirectly by means of a tappet  29 . Each pump element  24  has an inlet valve  38 , which opens into the pump working chamber  30  and via which the pump working chamber  30  is filled with fuel during the intake stroke of the pump piston  28  oriented radially inward toward the drive shaft  32 . Each pump element  24  also has an outlet valve  40 , which opens out from the pump working chamber  30  and via which the compressed fuel is displaced from the pump working chamber  30  during the delivery stroke of the pump piston  28  oriented radially outward. The inlet valve  38  and the outlet valve  40  are each embodied as a spring-loaded check valve. The drive shaft  32  with the cam  36  or eccentric and the support of the at least one pump piston  28  constitute a drive region  37  of the high-pressure pump  20  situated inside the pump housing  34 . 
     The high-pressure pump  14  delivers fuel via at least one line into a high-pressure region in which a reservoir  42 , for example, is situated. The reservoir  42  is connected to at least one injector  44 , which is mounted on a cylinder of the engine and injects fuel into the combustion chamber of the cylinder. It is also possible for the injectors  44  to be connected to the high-pressure pump  14  directly or indirectly via hydraulic lines  14 , which makes it possible to eliminate the separate reservoir  42 . The injector  44  has a fuel injection valve and, for example, an electrically actuated control valve that controls the opening and closing function of the fuel injection valve. It is also possible for the fuel injection valve to be directly controlled by means of an electrical actuator, for example a piezoelectric actuator. 
     The fuel injection device also has an electronic control unit  46  that controls the fuel injection. The control unit  46  triggers the injector  44  so that it injects a predetermined fuel quantity at a predetermined time. In the high-pressure region, a pressure sensor  48  is provided, which detects the pressure in the high-pressure region and is connected to the control unit  46 . It is possible for a connection from the reservoir  42  to a pressure-relief region, e.g. a return to the fuel tank  12 , to be provided, which is controlled by a pressure relief valve or pressure control valve  43 . 
     In the first exemplary embodiment shown in  FIG. 1 , between the delivery pump  10  and the intake side of the high-pressure pump  20 , a fuel metering device  50  is provided that is preferably situated between the fuel filter  22  and the intake side of the high-pressure pump  20 . The region between the delivery pump  10  and the intake side of the high-pressure pump  20  is referred to below as the low-pressure region. The fuel metering device  50  can be embodied so that it continuously or discretely adjusts a different-sized flow cross section in the connection between the delivery pump  10  and the intake side of the high-pressure pump  20 . Alternatively, the fuel metering device  50  can also be constituted by a cyclically operated valve that is opened and closed with a particular frequency; this valve opens a certain average flow cross section in accordance with its opening duration. The fuel metering device  50  can have an electric actuator  51  that can, for example, be embodied in the form of an electromagnet or a piezoelectric actuator, and is triggered by the control unit  46 . Alternatively, the fuel metering device  50  can also be hydraulically controlled. In this connection, the flow cross section is determined by a piston that can be moved as it is acted on by a hydraulic pressure. The hydraulic pressure can, for example, be produced by the discharge of the pressure control valve  43 . In this case, an increase in the discharge quantity of the pressure control valve  43  yields a higher pressure that reduces the flow cross section opened by the fuel metering device  50 . The pressure control valve  43  can be triggered by means of the control unit  46  so that the control unit  46  controls the fuel metering device  50  indirectly by means of the discharge quantity of the pressure control valve  43 . 
     Between the delivery pump  10  and the fuel metering device  50 , the fuel injection device is also equipped with an overflow valve  52  that controls a connection of the low-pressure region to a pressure-relief region. In this case, the pressure-relief region is embodied, for example, in the form of a return  53  leading to the fuel tank  12 ; a lower pressure prevails in the pressure-relief region than in the low-pressure region. The overflow valve  52  is embodied in the form of a pressure valve that opens when a predetermined pressure is reached in the low-pressure region, permitting fuel to flow out of the low-pressure region into the pressure-relief region. The opening pressure of the overflow valve  52  is determined by a spring  54  that acts on a valve closure member  55  of the overflow valve  52  in a closing direction. 
     In the first exemplary embodiment shown in  FIG. 1 , the connection between the delivery pump  10  and the intake side of the high-pressure pump  20  leads through the drive region  37  of the high-pressure pump  20  in which are situated the drive shaft  32  with its bearing points and the eccentric or cam  36  with the support of the at least one pump piston  28  or tappet  29 . The overflow valve  52  is situated downstream of the drive region  37 , between this region and the fuel metering device  50 . Consequently, the entire fuel quantity delivered by the delivery pump  10  first flows through the drive region of the high-pressure pump  20  before being drawn in by the high-pressure pump  20 . Alternatively, it is also possible for a connection into the drive region of the high-pressure pump  20  to lead from the connection leading from the delivery pump  10 , upstream of the fuel metering device  50 . In this case, however, only the part of the fuel quantity delivered by the delivery pump  10  that is not conveyed to the intake side of the high-pressure pump  20  through the fuel metering device  50  is available for the lubrication of the drive region of the high-pressure pump  20 . 
     The pressure prevailing in the low-pressure region between the fuel filter  22  and the intake side of the high-pressure pump  20  is detected by a pressure sensor  56  that is connected to the control unit  46 . Preferably, the pressure sensor  56  is situated in the low-pressure region between the fuel filter  22  and the drive region of the high-pressure pump  20  so that a possible pressure drop in the flow through the fuel filter  22  is taken into account in the pressure detection in the low-pressure region. According to the invention, the control unit  46  triggers the electric drive unit  14  of the delivery pump  10  as a function of at least one operating parameter of the internal combustion engine and/or of the high-pressure pump  20  in order to adjust a variable fuel quantity of the delivery pump  10  and therefore a variable pressure in the low-pressure region between the delivery pump  10  and the intake side of the high-pressure pump  20 . 
     One particular operating parameter that is taken into account in this case is the delivery quantity of the high-pressure pump  20 , which corresponds to the load of the engine. The higher the load of the engine is, the greater the delivery quantity of the high-pressure pump  20  must be in order to maintain a predetermined pressure in the reservoir  42  since more fuel is drawn from the reservoir  42  by the injectors  44  and injected into the engine. As another operating parameter, it is possible to take into account the speed of the engine, which is proportional to the speed of the high-pressure pump  20 . As an additional operating parameter, it is possible to take into account the fuel temperature that is detected by means of a fuel temperature sensor  58  that is connected to the control unit  46 . 
     The control unit  46  triggers the drive unit  14  of the delivery pump  10  so that with a higher load and therefore a greater delivery quantity of the high-pressure pump  20  and/or with a higher speed of the engine and the high-pressure pump  20 , the delivery pump  10  delivers a larger quantity of fuel into the low-pressure region and therefore a higher pressure is produced than with a low load and delivery quantity and/or low speed. In this case, with an increasing load of the engine and therefore with an increasing delivery quantity of the high-pressure pump  20 , it is possible for the control unit  46  to trigger the electric drive unit  14  of the delivery pump  10  so that the delivery pump  10  delivers an ever greater quantity of fuel and as a result, an ever greater pressure is produced in the low-pressure region. The fuel quantity delivered by the delivery pump  10 , which is not drawn in by the high-pressure pump  10  and is delivered into the reservoir  42 , is diverted into the pressure-relief region  53  by the overflow valve  52 . In this case, it is possible for the control unit  46  to increase the fuel quantity delivered by the fuel pump  10  disproportionately in relation to the fuel quantity to be delivered by the high-pressure pump  20  in order to assure a sufficient lubrication and/or cooling of the drive region  37  of the high-pressure pump  20 . The excess fuel quantity delivered by the delivery pump  10  is diverted from the low-pressure region by means of the overflow valve  52 . 
     Alternatively or in addition, it is possible for the control unit  46  to trigger the drive unit  14  of the delivery pump  10  so that with a high fuel temperature, the delivery pump  10  delivers a greater fuel quantity and as a result, a higher pressure is produced in the low-pressure region than with a low fuel temperature. In this case, it is possible that with an increasing fuel temperature, the control unit  46  triggers the drive unit  14  of the delivery pump  10  so that the delivery pump  10  delivers an increasing fuel quantity into the low-pressure region and as a result, a higher pressure is produced in the low-pressure region. This likewise assures a sufficient lubrication and/or cooling of the drive region  37  of the high-pressure pump  20  since the lubricating action of the fuel decreases as the fuel temperature rises. 
     Preferably, set point values for the pressure in the low-pressure region are stored in a characteristic map in the control unit  46 ; the control unit  46  then triggers the electric drive unit  14  of the delivery pump  10  so that the delivery pump  11  supplies the low-pressure region with the fuel quantity required to establish the set point value of the pressure. The characteristic of the overflow valve  52  is determined so that as the pressure in the low-pressure region increases, the overflow valve  52  diverts an increasing quantity of fuel into the pressure-relief region. The overflow valve  52  can, for example, have an at least approximately linear characteristic curve so that the fuel quantity diverted by means of the overflow valve  52  increases in proportion to the pressure in the low-pressure region.  FIG. 2  shows a graph depicting, by way of example, the region A is in which the fuel quantity V delivered by the delivery pump  10  is plotted over the pressure pND prevailing in the low-pressure region. Also by way of example, the graph in  FIG. 2  shows the characteristic curve B of the overflow valve  52 , i.e. the fuel quantity V diverted by means of this valve as a function of the pressure pND prevailing in the low-pressure region. The working region of the overflow valve  52 , i.e. the pressure region in which the overflow valve  52  diverts fuel from the low-pressure region, is labeled C in  FIG. 3 . 
     The overflow valve  52  is designed so that it is able to divert fuel—which is delivered by the delivery pump  10 —from the low-pressure region, independent of the setting of the fuel metering device  50 . The overflow valve  52  thus permits a variable setting of the pressure in the low-pressure region and therefore of the delivery quantity of the delivery pump  10 , independent of the fuel quantity to be delivered by the high-pressure pump  20 . This makes it possible to improve the lubrication and/or cooling of the drive region of the high-pressure pump  20  as needed, independent of the fuel quantity to be delivered by the high-pressure pump  20 . 
     With a low load of the high-pressure pump  20 , i.e. a low delivery quantity and/or low fuel temperature, the pressure that the delivery pump  10  produces in the low-pressure region can be kept low, for which purpose the delivery pump  10  need only supply a small quantity of fuel, thus making it possible to minimize the load on the delivery pump  10 , in particular on its electric drive unit  14 , thus also minimizing the electrical energy required to power it. The delivery pump  10  with the electric drive unit  14  can therefore be designed for a lower average load, thus permitting its design to be simplified in comparison to a design with a constant delivery quantity or permitting an extended service life to be achieved in comparison to said design. Alternatively, it is also possible—without limiting the service life of the delivery pump  10 —to permit an increased peak load with a large delivery quantity of the delivery pump  10  since this is only required for a short period of time. 
     The variable delivery quantity of the delivery pump  10  also reduces the load on the fuel filter  22  since it does not have the maximum delivery quantity of the delivery pump  10  flowing through it at all times, but rather only the delivery quantity of the delivery pump  10  that is actually required. The fuel filter  22  can therefore be dimensioned as smaller than in a conventional design for a constant delivery quantity of the delivery pump  10  or, with the same dimensioning, can achieve a longer service life. In addition, by increasing the fuel quantity that it delivers, the fuel pump  10  can at least partially compensate for a pressure drop occurring due to contamination of the fuel filter  22  as the flow passes through it. 
       FIG. 3  shows a the fuel injection device according to a second exemplary embodiment in which, by contrast with the first exemplary embodiment, the fuel metering device and possibly the overflow valve can be eliminated. The delivery pump  10  is equipped with the electric drive unit  14 , which is triggered by the control unit  46 . The fuel filter  22  is situated between the delivery pump  10  and the intake side of the high-pressure pump  20 ; the pressure sensor  56  that is connected to the control unit  46  is situated in the low-pressure region between the fuel filter  22  and the intake side of the high-pressure pump  20 ; the pressure that the pressure sensor  56  detects in the low-pressure region serves as a control variable for the control unit  46  in the triggering of the drive unit  14  of the delivery pump  10 . It is also possible for the high-pressure region to contain the pressure sensor  48 , which detects the pressure in the high-pressure region and is connected to the control unit  46 . The high-pressure region can also contain the pressure relief valve or pressure control valve  43 . A pressure control valve  60  is situated between the delivery pump  10  and the fuel filter  22  in order to prevent damage to the delivery pump  10  and/or the fuel filter  22  in the event of excessive pressure. 
     In the second exemplary embodiment of the fuel injection device, the fuel quantity delivered by the delivery pump  10  can be variably adjusted in order to variably adjust the quantity of fuel drawn in by the high-pressure pump  20  and delivered to the high-pressure region. The pressure that the delivery pump  10  produces in the low-pressure region can thus be kept essentially constant within predetermined limits. The control unit  46  triggers the drive unit  14  of the delivery pump  10  so that the delivery pump  10  supplies the intake side of the high-pressure pump  20  with a delivery quantity and the high-pressure pump in turn supplies the reservoir  42  with a fuel quantity that is sufficient to maintain a predetermined pressure in the reservoir  42 . As the load on the internal combustion engine increases, the high-pressure pump  20  must deliver an increasing quantity of fuel into the reservoir  42  and the delivery pump  10  must deliver a correspondingly increasing quantity of fuel to the intake side of the high-pressure pump  20  in order to maintain the predetermined pressure in the low-pressure region. In this case, it is possible to eliminate the fuel metering device  50 . 
     As an operating parameter of the engine and of the high-pressure pump  20 , preferably their speeds can be taken into account by the control unit  46  and a pilot control of the pressure in the low-pressure region can take place so that as the speed increases, the delivery pump  10  delivers a larger quantity of fuel and a higher pressure is produced in the low-pressure region. Particularly in the idling mode of the internal combustion engine, the quantity of fuel delivered by the delivery pump  10  and therefore the pressure in the low-pressure region can be kept low, thus minimizing the required drive output for the delivery pump  10 . As in the first exemplary embodiment, the fuel metering device  50  can be provided to adjust the delivery quantity of the high-pressure pump  20 . 
     It is possible for at least part of the fuel quantity, which the delivery pump  10  delivers into the low-pressure region, to be supplied to the drive region  37  of the high-pressure pump  20  for lubrication and/or cooling. Preferably, the drive unit  14  of the delivery pump  10  is triggered by the control unit  46  so that the delivery pump  10  always delivers a minimum fuel quantity required to assure sufficient lubrication and/or cooling of the drive region  37  of the high-pressure pump  20 . 
     In the fuel injection device according to the second exemplary embodiment, it is also possible to implement a monitoring of the low-pressure region for leaks since the presence of a leak can be ascertained based on the occurrence of a rapid pressure drop in the low-pressure region. With a changing, wear-induced leakage that occurs in the high-pressure pump  20  over the operation period of the high-pressure pump, only slow pressure drops occur in the low-pressure region, thus permitting clear differentiation here. If the control unit  46  detects a leak, it is possible, for example, to prevent further operation of the engine or to issue a warning to the vehicle driver. 
     The foregoing relates to the preferred exemplary embodiments of the invention, it being understood that other variants and embodiments thereof are possible within the spirit and scope of the invention, the latter being defined by the appended claims.