Abstract:
A method for operating a fuel delivery device of an internal combustion engine includes switching an electromagnetic actuating device of a volume control valve so as to set a delivery volume. An intensity of an energy that is supplied to the electromagnetic actuating device for switching purposes, in particular of a current supplied to the electromagnetic actuating device and/or a level of a voltage applied to the electromagnetic actuating device, depends at least intermittently on a rotational speed of the internal combustion engine.

Description:
This application is a 35 U.S.C. §371 National Stage Application of PCT/EP2012/057985, filed on May 2, 2012, which claims the benefit of priority to Serial No. DE 10 2011 077 991.4, filed on Jun. 22, 2011 in Germany, the disclosures of which are incorporated herein by reference in their entirety. 
     BACKGROUND 
     The disclosure relates to a method as described herein, and to a computer program and to an open-loop and/or a closed-loop control device as described herein. 
     Quantity control valves, for example in a fuel delivery device of an internal combustion engine, are known commercially. Quantity control valves are generally operated electromagnetically and are frequently an integral component of a high pressure pump of the fuel delivery device. The quantity control valve controls the fuel quantity pumped to a high pressure accumulator (“rail”) from where fuel is conducted to the injection valves of the internal combustion engine. An armature which is coupled to a valve body of the quantity control valve can be moved by magnetic force. The valve body, usually an inlet valve of the high pressure pump, can impact against a valve seat, or be lifted off from the valve seat. As a result, a fuel quantity of the internal combustion engine can be regulated. 
     A patent publication from this specialist field is, for example, EP 1 042 607 B1. 
     SUMMARY 
     The problem on which the disclosure is based is solved by a method as described herein and by a computer program and an open-loop and/or closed-loop control device according to the disclosure. Advantageous developments are specified herein. Features which are important for the disclosure are also to be found in the following description and in the drawings, wherein the features may be important for the disclosure either alone or in different combinations, without being explicitly referred to again. 
     The method according to the disclosure has the advantage that a quantity control valve (metering device) of a fuel delivery device can be activated with comparatively little electrical energy, in particular while an internal combustion engine is operated at medium or low rotational speeds. The operational noise of the quantity control valve can be reduced and the endurance strength increased. 
     The disclosure relates to a method for operating a fuel delivery device of an internal combustion engine, in which, in order to set a delivery quantity, an electromagnetic activation device of a quantity control valve, arranged in an inflow of a delivery space of the fuel delivery device, is switched. For this purpose, during every switching process during which an armature is to be moved in the direction of a stroke stop, energy is fed to the electromagnetic activation device by means of the actuation. For example, the switching of the quantity control valve takes place twice, three times or even four times during one rotation of a cam shaft of the internal combustion engine. Comparatively high levels of energy are necessary to reliably switch the quantity control valve and to achieve short switching times even at the highest possible rotational speed of the cam shaft and/or of the internal combustion engine. 
     The disclosure is based on the idea that at rotational speeds below the maximum rotational speed the requirement for a short switching time is correspondingly less critical. As a result, according to the disclosure, the amount of energy which is fed to the electromagnetic activation device for the purpose of switching, in particular the amount of current which is fed to the electromagnetic activation device and/or a level of a voltage which is applied to the electromagnetic activation device, is made to depend at least for a certain time on a rotational speed of the cam shaft or of the internal combustion engine, specifically to the effect that it is smaller at low rotational speeds than at high ones. 
     One refinement of the disclosure provides that the energy depends on the rotational speed of the internal combustion engine only during an attraction phase during which the armature of the electromagnetic activation device is moved from a first into a second position. The attraction phase requires a particularly large amount of energy in order to achieve a respectively required short switching time. The necessary dependence of the actuation on the rotational speed of the internal combustion engine during the attraction phase is therefore particularly efficient. The actuation of the electromagnetic activation device during a holding phase following the attraction phase can take place substantially independently of the rotational speed. 
     Furthermore there is provision that the energy is increased with a rising rotational speed, wherein the relationship is monotonous. This takes into account the fact that the movement of the armature has to occur generally more quickly in accordance with the rotational speed. This preferably occurs using a continuous and monotonous characteristic curve. 
     In particular there is provision that the energy is controlled in such a way that the quantity control valve can be switched reliably within a time interval which is provided for a respective rotational speed. The time interval is generally longer for relatively low rotational speeds than for relatively high rotational speeds and is to be respectively dimensioned in such a way that the quantity control valve can operate correctly. The room for maneuver in terms of timing which is possible as a result is used according to the disclosure to extend an attraction duration of the armature at low rotational speeds within the scope of the respective time interval. This requires a respectively smaller quantity of energy. 
     One refinement of the method provides that the current and/or the voltage for actuating the electromagnetic activation device are clocked. For example, the electromagnetic activation device is connected to an operating voltage repeatedly by means of an electronic switch during the attraction phase and/or the holding phase of the armature and it is disconnected therefrom again. A pulse duty factor which is set in the process therefore determines the average current during the actuation. The pulse duty factor is set in such a way that the average current depends on the rotational speed of the internal combustion engine. The electronic switch is preferably activated as a function of in each case a lower and an upper current threshold. If the current flowing through a coil of the electromagnetic activation device undershoots the lower current threshold, the electronic switch is closed and therefore the coil is connected to the operating voltage. As a result, the current flowing via the coil, and a magnetic force brought about as a result, increase continuously. If the current flowing through the coil exceeds the upper current threshold, the electronic switch is opened and therefore the coil is disconnected from the operating voltage. This reduces the current flowing via the coil, and correspondingly the magnetic force, continuously. In general, the current thresholds used for the attraction phase and the holding phase are respectively different. 
     As an alternative to using current thresholds it is also possible to actuate the electromagnetic activation device by means of a “pilot-controlled” pulse-width-modulated voltage, wherein the determining parameters for at least one actuation in each case are set in advance. According to the disclosure, these parameters are set in such a way that the quantity of energy fed to the electromagnetic activation device for the purpose of switching depends at least for a certain time on the rotational speed of the internal combustion engine. 
     The method can be carried out particularly easily if it is carried out by means of a computer program on an open-loop and/or closed-loop control device (“control unit”) of the internal combustion engine. In one preferred refinement, the control unit is set up by loading the computer program with the features described herein from a storage medium. The storage medium is understood in this respect to be any device which contains the computer program in a stored form. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the disclosure are explained below with reference to the drawings, in which: 
         FIG. 1  shows a simplified diagram of a fuel delivery device of an internal combustion engine; 
         FIG. 2  shows a sectional illustration of a high pressure pump of the fuel delivery device together with a quantity control valve and an electromagnetic activation device; 
         FIG. 3  shows a timing diagram of actuation of the electromagnetic activation device; 
         FIG. 4  shows a diagram of an attraction current and of an attraction time plotted against a rotational speed of the internal combustion engine; and 
         FIG. 5  shows a simplified block diagram for supplementary illustration of the method. 
     
    
    
     DETAILED DESCRIPTION 
     In all the figures, the same reference symbols are used for functionally equivalent elements and variables even in different embodiments. 
       FIG. 1  shows a fuel delivery device  1  of an internal combustion engine in a highly simplified illustration. Fuel is fed from a fuel tank  3  via a suction line  4 , by means of a predelivery pump  5 , via a low pressure line  7  and via a quantity control valve  10 , which can be activated by an electromagnetic activation device  9  (“electromagnet”), of a high pressure pump  11  (not explained further here). The high pressure pump  11  is connected to a high pressure accumulator  13  (“common rail”) downstream via a high pressure line  12 . Other elements such as, for example, valves of the high pressure pump  11 , are not shown in  FIG. 1 . The electromagnetic activation device  9  is actuated by means of an open-loop and/or closed-loop control device  16  on which a computer program  18  can run. 
     Of course, the quantity control valve  10  can also be embodied as one structural unit with the high pressure pump  11 . For example, the quantity control valve  10  can be a forced-opening inlet valve of the high pressure pump  11 . Alternatively, the quantity control valve  10  can also have an activation device other than the electromagnet  9 , for example a piezo-actuator. 
     During the operation of the fuel delivery device  1 , the predelivery pump  5  delivers fuel from the fuel tank  3  into the low pressure line  7 . In the process, the quantity control valve  10  controls the fuel quantity fed to a working space of the high pressure pump  11  in that an armature of the electromagnet  9  is moved from a first into a second position, and vice versa. The quantity control valve  10  can therefore be closed and opened. 
       FIG. 2  shows a detail of a sectional illustration (longitudinal section) of the high pressure pump  11  of the fuel delivery device  1  together with the quantity control valve  10  and the electromagnetic activation device  9 . The illustrated arrangement comprises a housing  20  in which the electromagnetic activation device  9  is arranged in the upper region in the drawing, the quantity control valve  10  is arranged in the central region, and a delivery space  22  together with a piston  24  of the high pressure pump  11  is arranged in the lower region. 
     The electromagnetic activation device  9  is arranged in a valve housing  26  and comprises a coil  28 , an armature  30 , a pole core  32 , an armature spring  34 , a rest seat  36  and a stroke stop  38 . The rest seat  36  constitutes the first position of the armature  30 , and the stroke stop  38  constitutes the second position of the armature  30 . The armature  30  acts on a valve body  42  by means of a coupling element  40 . An associated sealing seat  44  is arranged above the valve body  42  in the drawing. The sealing seat  44  is part of a pot-shaped housing element  46  which encloses, inter alia, the valve body  42  and the valve spring  48 . The sealing seat  44  and the valve body  42  form the inlet valve of the high pressure pump  11 . 
     The non-energized state of the electromagnetic activation device  9  is illustrated in  FIG. 2 . In this context, the armature  30  is pressed downward in the drawing, against the rest seat  36 , by means of the armature spring  34 . As a result, the valve body  42  is acted on via the coupling element  40  counter to the force of the valve spring  48 , as a result of which the inlet valve and/or the quantity control valve  10  are/is opened. As a result, a fluidic connection is produced between the low pressure line  7  and the delivery space  22 . 
     In the energized state of the electromagnetic activation device  9 , the armature  30  is magnetically attracted by the pole core  32 , as a result of which the coupling element  40 , coupled to the armature  30 , is moved upward in the drawing. As a result, given corresponding fluidic pressure conditions, the valve body  42  can be pressed against the valve seat  44  by the force of the valve spring  48 , and thus close the inlet valve and/or the quantity control valve  10 . This can occur, for example, when the piston  24  carries out a working movement (upward in the drawing) in the delivery space  22 , wherein fuel can be delivered into the high pressure line  12  via a non-return valve  60  (opened here). 
     The opening and/or the closing of the quantity control valve  10  occur as a function of a plurality of variables: firstly, as a function of the forces applied by the armature spring  34  and the valve spring  48 . Secondly, as a function of the fuel pressure prevailing in the low pressure line  7  and the delivery space  22 . Thirdly, as a function of the force of the armature  30 , which force is determined substantially by a current I flowing through the coil  28  at that particular time. In particular, the current I can influence, again also as a function of the respective fuel pressures, the time of opening or closing of the valve body  42 , and can therefore substantially control the quantity of fuel to be delivered. 
       FIG. 3  shows a timing diagram of actuation of the quantity control valve  10 . In the co-ordinate system illustrated in the drawing, currents I1 (continuous line) and I2 (dashed line) which flow across the coil of the electromagnetic activation device  9  are plotted against a time t. A double arrow  62  characterizes the energization for an attraction phase, and a double arrow  64  characterizes the energization for a holding phase of the armature  30  of the electromagnetic activation device  9 . During the attraction phase, the armature is moved by magnetic force from the rest seat  36  as far as the stroke stop  38 . During the holding phase, the armature  30  is held in its position against the stroke stop  38  by a, generally smaller, magnetic force. Below, firstly the profile of the current I1 is described, said current I1 being used to actuate the electromagnetic activation device  9  at a comparatively high rotational speed  72  (cf.  FIG. 4 ) of the internal combustion engine. 
     The attraction phase begins at a time t0, wherein the current I1 rises comparatively quickly, and is clocked about a mean value  66   a  starting from a time t1a. At a time t2 the energization for the holding phase begins, wherein the current I1 is clocked about a mean value  68 . The mean value  68  is lower than the mean value  66   a . At a time t3, the actuation is ended, as a result of which the current I1 is quickly reduced to zero. 
     In the case of a relatively low rotational speed  72  of the internal combustion engine, the electromagnetic activation device  9  is actuated with a current I2, that is to say switching thresholds (not illustrated) which control the switching on and the switching off of the current I2 during the attraction phase, are set to lower values with respect to switching thresholds of the current I1. As a result, a correspondingly lower mean value  66   b  occurs for the profile of the current I2 during the attraction phase. The required level of energy during the attraction phase is therefore also lower and operating noise during the impacting of the armature  30  against the stroke stop  38  is reduced. In the process, at the same time an attraction duration of the armature  30  is prolonged, wherein the time difference is prolonged between t2 and t0, and as a result the attraction phase  62  is lengthened, without however the correct function of the quantity control valve  10  being adversely affected. 
     The switching thresholds (not illustrated) which determine the profiles of the currents I1 and I2, or the mean values  66   a  and  66   b  which result therefrom, are respectively selected in such a way that reliable impacting of the armature  30  against the stroke stop  38 , and therefore reliable switching of the quantity control valve  10 , are made possible in all operating cases. Due to the current I2 which is on average lower during the attraction phase, the armature  30  is accelerated with a relatively small force compared to the current I1, and said armature  30  correspondingly impacts in a delayed fashion. This is explained in more detail below with  FIG. 4 . 
       FIG. 4  shows a co-ordinate system in which mean values  66  of a current I flowing via the coil  28  during the attraction phase as well as associated attraction durations  70  are plotted linearly against a rotational speed  72  of the internal combustion engine. The attraction duration  70  characterizes the time period from the beginning of the energization of the coil  28  at the time t0 up to the first impacting of the armature  30  against the stroke stop  38 . The mean values  66  are determined here by reference points  74  which can be stored, for example, in a characteristic diagram of the open-loop and/or closed-loop control device  16  of the internal combustion engine. The mean values  66  of the current I also characterize an energy level which is fed to the electromagnetic activation device  9  during the attraction phase, in particular if the coil  28  is connected to a constant source voltage during the attraction phase. 
     It is apparent that the mean values  66  of the current I increase monotonously as the rotational speed  72  rises. If the piston  24  of the high pressure pump  11  is also moved as a function of the rotational speed  72 , the possible time period to the movement of the valve body  42  or of the armature  30  becomes correspondingly shorter, that is to say more critical. This fact is allowed for suitably by the attraction durations  70  which reduce as the energization becomes stronger. This occurs, as already described above, in such a way that reliable switching of the quantity control valve  10  is made possible at any rotational speed  72 . 
       FIG. 5  shows a simplified flow chart of the actuation of the electromagnetic activation device  9 . The illustrated method is preferably carried out by means of the computer program  18  in the open-loop and/or closed-loop control device  16  of the internal combustion engine. In a first block  76 , the illustrated procedure begins, wherein the current rotational speed  72  of the internal combustion engine is determined. In a second block  78 , two reference points  74  are read out from a characteristic diagram on the basis of the determined rotational speed  72 . After this, interpolation is carried out between these two reference points  74  in order to determine a respective mean value  66  in a way which is precisely matched to the rotational speed  72 . Suitable switching thresholds (without reference symbols) for the switching on and the switching off of the current I are determined from the mean value  66 . 
     In a third block  80 , the determined switching thresholds are used to actuate the electromagnetic activation device  9  or the coil  28  during the attraction phase of the armature  30 . The method in  FIG. 5  can be repeated cyclically.