Patent Publication Number: US-9410516-B2

Title: Method for operating a fuel system for an internal combustion engine

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method, a control device, and a computer program for operating a fuel system for an internal combustion engine. 
     2. Description of the Related Art 
     Fuel supply control valves, for example in a fuel system of an internal combustion engine, are known from the market. Fuel supply control valves are generally operated electromagnetically as switching valves having two switching positions, and frequently are an integral part of a high-pressure pump of the fuel system. The fuel supply control valve controls the fuel quantity pumped to a high-pressure accumulator (“rail”), from which fuel is led to the injectors of the internal combustion engine. An armature which is coupled to a valve element of the fuel supply control valve may be moved by magnetic force. The valve element, usually an inlet valve of the high-pressure pump, may strike against a valve seat or may be lifted from the valve seat. A supplied fuel quantity for the internal combustion engine, and thus, ultimately, the pressure in the rail, may be regulated in this way. A published German patent application document in this field is DE 10 2007 035 316 A1, for example. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention has the advantage that an energization of an electrical actuating device for a metering device of a fuel system for an internal combustion engine may be reduced (so-called “reduced current control”). A speed of moving elements of the metering device as well as operating noise of the metering device, in particular in a low-speed range of the internal combustion engine, may be reduced in this way. The method according to the present invention allows the energization to be reduced as a function of a particular specimen of the metering device. Reliable switching of the metering device may still be achieved, essentially independently of specimen variations, temperatures, or an ohmic resistance of supply lines of the electrical actuating device. 
     The present invention relates to a method for operating a fuel system for an internal combustion engine, the metering device for measuring a delivery quantity of the fuel being openable and/or closable with the aid of the electrical actuating device, and a valve element of the metering device may switch into a first position when the actuating device is not activated, and into a second position when the actuating device is activated. The first position corresponds to a closed metering device, and the second position corresponds to an open metering device. In a first alternative, the method is characterized by the following steps:
     (a) activating the electrical actuating device in at least one first cycle in such a way that the valve element reliably switches into the second position;   (b) activating the electrical actuating device in at least one second cycle in such a way that the electrical actuating device is activated from activation to activation, with activation energy which decreases gradually, until a limiting case is reached in which the valve element only just or just no longer switches into the second position;   (c) ascertaining a first activation energy, which corresponds to the limiting case;   (d) subsequently activating the actuating device, taking the first activation energy into account.   

     Thus, starting from an activation of the electrical actuating device that is sufficient for reliably switching into the second position, the activation energy is reduced gradually, and the limiting case is “felt out,” so to speak, “from above.” At the same time, the first activation energy which is part of the limiting case is ascertained and subsequently used as a reference value for activating the electrical actuating device. The first activation energy is thus at least necessary as a limiting case in order to reliably switch the electrical actuating device. The electrical actuating device is preferably designed as an electromagnetic actuating device, and includes a coil and an armature which is movable by magnetic force. Alternatively, it is also conceivable to carry out the method according to the present invention with an electrical actuating device which includes a piezoactuator. The metering device corresponds to a so-called fuel supply control valve which includes, for example, an inlet valve situated upstream from a fuel pump of the fuel system. 
     A second alternative for ascertaining the limiting case is characterized by the following steps:
     (a) activating the electrical actuating device in at least one first cycle in such a way that the valve element does not reliably switch into the second position;   (b) activating the electrical actuating device in at least one second cycle in such a way that the electrical actuating device is activated from activation to activation, with activation energy which increases gradually, until a limiting case is reached in which the valve element only just or just no longer switches into the second position;   (c) ascertaining the first activation energy, which corresponds to the limiting case;   (d) subsequently activating the actuating device, taking the first activation energy into account.   

     The second alternative of the method is thus analogously carried out in reverse order with respect to the first alternative. The activation energy is increased gradually, and the limiting case is “felt out,” so to speak, “from below.” Both described alternatives result in the same limiting case and the same first activation energy. It is understood that in both alternatives, the activation energy may also be gradually increased and decreased in alternation in a range around the presumed limiting case in order to accurately “sound out” the limiting case. Likewise, it is understood that in steps (b) the activation energy does not necessarily have to be changed in a strictly monotonic manner with each subsequent activation. Thus, it is certainly possible for multiple successive activations to use the same activation energy. 
     In the present case, “activation energy” is generally understood to mean a variation in time of a current flowing through the electrical actuating device. A switching characteristic of the electrical actuating device is thus a function of the time curve of the current (“current profile”) corresponding to an associated time integral. The time integral of the current multiplied by a voltage has the dimension of energy. 
     In one embodiment of the method, after step (c) the first activation energy is increased by an offset value, resulting in a second activation energy, the offset value being dimensioned in such a way that the valve element may robustly switch into the second position. The subsequent activation in step (d) with the second activation energy takes place in a similar way. The reliability of the switching corresponding to the offset value may thus be optionally improved, in that it becomes more robust with regard to disturbances such as changes in temperature and/or changes in voltage. 
     In one preferred embodiment of the method, the first position corresponds to a closed metering device, and the second position corresponds to an open metering device. As a result, it is possible for the metering device in the de-energized state to be closed by devices which control the fuel system, and for the fuel to not be able to flow uncontrolled. The fuel system may thus be kept in a defined state. 
     In a first option according to the present invention for ascertaining the limiting case, a pressure and/or a pressure change and/or a rate of pressure change in a pressure accumulator, in particular in a high-pressure accumulator (“rail”), of the fuel system is/are ascertained and compared to a threshold value. The limiting case may be recognized, for example, by a rise in the rail pressure over time. Appropriate threshold values may be predefined for this purpose. It may thus be ascertained, for example, whether a certain fuel pressure is exceeded, and/or whether, starting from an initial value of the fuel pressure, a pressure change has exceeded a predefined threshold value, and/or whether the rate of pressure change has exceeded a predefined threshold value. The limiting case may thus be ascertained in a particularly precise way. 
     In a second option according to the present invention for ascertaining the limiting case, a voltage and/or a current of the electrical actuating device is/are ascertained and evaluated. Comparatively rapid changes in the movement of the valve element result in a corresponding change in the movement of the armature, and thus, a corresponding change in a magnetic field surrounding the armature. According to Faraday&#39;s law of induction, a voltage is thus generated in a coil of the electromagnetic actuating device which is ascertainable at terminals of the electromagnetic actuating device. 
     In addition, it may be provided that the second activation energy and/or a time curve of the activation corresponding to the second activation energy or a time curve of the current is/are stored in a data store, using a characteristic map, for example. Thus, for the subsequent activation of the electromagnetic actuating device, the stored value may be read out from the data store, and therefore needs to be ascertained only occasionally or periodically during operation of the metering device. The availability of the stored final state may thus be increased by dispensing with the adaptation operations. In addition, it may be provided to store further variables or parameters, for example a speed of the internal combustion engine together with the activation energy or the time curve of the current. 
     A first alternative of the activation of the electromagnetic actuating device provides that a time curve of the activation includes a first phase having a monotonically increasing current curve, and that the time curve includes a subsequent second phase in which the electrical actuating device is activated with the aid of a pulse width modulation, and that a duration of the first phase and/or a pulse duty factor of the pulse width modulation within the second phase is/are changed in order to ascertain the limiting case. A first temporal “current profile” is thus described which is particularly suitable for carrying out the method. 
     A second alternative of the activation of the electromagnetic actuating device provides that the time curve of the activation includes a first phase having a monotonically increasing current curve, and that the time curve includes a subsequent second phase in which the electrical actuating device is energized with the aid of a regulatable current, and that a duration of the first phase and/or an intensity of the regulatable current within the second phase is/are changed in order to ascertain the limiting case. A second temporal “current profile” is thus described which is particularly suitable for carrying out the method. 
     A third alternative of the activation of the electromagnetic actuating device provides that the time curve of the activation includes a first phase in which the electrical actuating device is energized with the aid of a first regulatable current, and that the time curve includes a subsequent second phase in which the electrical actuating device is energized with the aid of a second regulatable current, the second current being lower than the first current, and that a duration of the first phase and/or an intensity of the second regulatable current is/are changed in order to ascertain the limiting case. A third temporal “current profile” is thus described which is particularly suitable for carrying out the method. 
     In addition, in the above-described three alternatives, the time curve of the activation may include a third phase, following the second phase, in which the electrical actuating is activated or energized with the aid of a pulse width modulation or a third regulatable current. Any premature drop of the valve element from the second position back into the first position due to currents which are possibly too low may thus be avoided. The effective current is generally higher in the third phase than in the second phase. 
     According to another embodiment of the method, the above-described offset value may be predefined as a function of the fuel pressure in the pressure accumulator and/or a fuel temperature and/or an electrical resistance of electrical lines attached to the electrical actuating device. The offset value may thus be dimensioned to be compatible with the existing operating parameters, so that the offset value may be selected to be comparatively small. The second activation energy is thus appropriately low without reducing the reliability of the switching of the valve element. Multiple offset values may preferably be stored as a function of multiple operating parameters in a characteristic map of the control and/or regulation device for the internal combustion engine. 
     The mentioned control and/or regulation device for the internal combustion engine is particularly useful for the method according to the present invention, since it already centrally contains a number of operating variables of the fuel system and the internal combustion engine for carrying out the method. The method is preferably carried out with the aid of a computer program. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a fuel system for an internal combustion engine. 
         FIG. 2  shows a fuel supply device which includes a metering device, an electrical actuating device, and a fuel pump. 
         FIG. 3  shows a time diagram for an activation of the electrical actuating device. 
         FIG. 4  shows a time diagram with currents for activating the electrical actuating device. 
         FIG. 5  shows a time diagram with time curves of operating noise of the electrical actuating device. 
         FIG. 6  shows a flow chart for carrying out a method for operating the fuel system. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The same reference numerals are used for functionally equivalent elements and variables in all the figures, even for different specific embodiments. 
       FIG. 1  shows a fuel system  10  for an internal combustion engine (not illustrated) in a greatly simplified illustration. Fuel is supplied from a fuel tank  12 , via an intake line  14  with the aid of a pre-feed pump  16 , via a low-pressure line  18 , and via a fuel supply control valve  22 , which is activatable by an electrical actuating device  20  (designed as an electromagnetic actuating device in the present case), to a piston pump  24  (high-pressure pump) which is mechanically driven by the internal combustion engine. Fuel supply control valve  22  forms a metering device for measuring a supplied quantity of the fuel. 
     Downstream, piston pump  24  is connected to a pressure accumulator  28  (high-pressure accumulator, “common rail”) via a high-pressure line  26 . A pressure sensor  30  is situated at pressure accumulator  28 . Piston pump  24  includes a piston  32 , which in the drawing is vertically movable, and in the present case drivable with the aid of an eccentric disk  34 . Electrical actuating device  20  is activated by a control and/or regulation device  36  via electrical lines  35 . Control and/or regulation device  36  includes a data store  37  and a computer program  39 . In addition, control and/or regulation device  36  is connected to pressure sensor  30  via an electrical line  38 . 
     It is understood that fuel supply control valve  22  may also be designed as a unit with piston pump  24  (see  FIG. 2 ). In particular, fuel supply control valve  22  may be a forcibly openable inlet valve  48  (see  FIG. 2 ) of piston pump  24 . 
     During operation of fuel system  10 , pre-feed pump  16  conveys fuel from fuel tank  12  into low-pressure line  18 . Fuel supply control valve  22  controls the quantity of fuel that is supplied to a feed chamber  25  of piston pump  24 . Fuel supply control valve  22  may be closed and opened as a function of a particular need for fuel. The fuel is gasoline or diesel fuel, for example. 
       FIG. 2  shows piston pump  24  from  FIG. 1  together with fuel supply control valve  22  and electrical actuating device  20  in a slightly more detailed but likewise schematic illustration. Piston pump  24  includes a housing  40  in which electrical actuating device  20 , which includes a solenoid  42  and an armature  44 , is situated in the left section of the drawing. A resting seat  43  for armature  44  is situated in the end section of housing  40 , at the left in the drawing. 
     In addition, piston pump  24  includes an inlet  46  which is connected to low-pressure line  18  via inlet valve  48 , and an outlet  50  which is connected to high-pressure line  26  via an outlet valve  52 . Inlet valve  48  includes a valve spring  53  and a valve element  54 . Inlet valve  48  is hydraulically connected to feed chamber  25  via an opening (no reference numeral). 
     Valve element  54  may be forcibly held in a second position  47  (illustrated in dashed lines) with the aid of a valve needle  55 , which is horizontally displaceable in the drawing and coupled to armature  44 . A first position  45  corresponds to a closed metering device  22 , and second position  47  corresponds to an open metering device  22 . 
     If electrical actuating device  20  is not energized, inlet valve  48  may be closed by the force of valve spring  53  (“closed in the de-energized state”). When electrical actuating device  20  is energized, armature  44  may be moved to the right in the drawing against a lift stop  49  with the aid of magnetic force, and valve element  54  may thus forcibly switch from first position  45  into second position  47 . As a result, inlet valve  48  opens. Due to the (active) switching of armature  44  or of valve element  54 , operating noise may occur which corresponds to the particular intensity of the activation of electrical actuating device  20 . 
     During operation of fuel system  10 , piston pump  24  conveys fuel from inlet  46  to outlet  50 , outlet valve  52  opening or closing, corresponding to a particular pressure difference between feed chamber  25  and outlet  50 . At full delivery of piston pump  24 , inlet valve  48  is acted on by a particular pressure difference between inlet  46  and feed chamber  25 . For a desired partial delivery, starting at a predefined point in time, electrical actuating device  20  is energized during a delivery stroke, as the result of which inlet valve  48  is not able to close, and the fuel that is still present in feed chamber  25  is conveyed back into low-pressure line  18 . The volumes of piston pump  24  situated within housing  40  are essentially filled with fuel. 
       FIG. 3  shows a time diagram for an activation of electrical actuating device  20 . A time diagram at the top of the drawing shows an activation voltage  58  which is connected at a first terminal of solenoid  42 . A middle time diagram in the drawing shows a current  60  associated with activation voltage  58 . A bottom time diagram in the drawing shows a lift  62  of armature  44  associated with voltage  58  and current  60 . 
     The diagrams have the same time scale (time t). All three diagrams have a respective zero value of activation voltage  58  and of current  60  and of lift  62 , which is shown slightly above an associated abscissa. All three diagrams have a first time range  64 , which corresponds to a pick-up phase of armature  44 , and a subsequent second time range  66 , which corresponds to an energization during a holding phase of armature  44  at lift stop  49 . In the bottom diagram, the zero value corresponds to a stop of armature  44  against resting seat  43 , and a horizontal dashed line corresponds to lift stop  49 . 
     The activation of solenoid  42  and of electrical actuating device  20  illustrated in  FIG. 3  has a “reduced current profile” in which a pick-up speed of armature  44  in the direction of second position  47  of valve element  54  is comparatively low, and an associated pick-up duration  68  is correspondingly great. Thus, the illustrated current profile may be used for switching valve element  54 , in particular at comparatively low speeds of the internal combustion engine. 
     Activation voltage  58  is depicted in the top diagram. A second terminal (not illustrated) of solenoid  42  is continuously switched against a battery voltage  70 . The first terminal (not illustrated) of solenoid  42  may be switched between battery voltage  70  and a ground potential (“0”) with the aid of an electronic switch, as the result of which solenoid  42  and electrical actuating device  20  are activated, and current  60  may flow. 
     A first phase  72  of an activation begins at a point in time t0. Activation voltage  58  is continuously switched to zero during first phase  72 , as the result of which current  60  in solenoid  42  rises in an approximately ramp-shaped manner. At a subsequent point in time t1, at which armature  44  has not yet struck against lift stop  49 , first phase  72  ends and a second phase  74  begins. During second phase  74 , activation voltage  58  is clocked in the manner of a pulse width modulation, and current  60  assumes an approximately sawtooth-shaped time curve. Armature  44  strikes against lift stop  49  at a subsequent point in time t2. A pick-up duration (t2−t0) of armature  44  is longer than a duration (t1−t0) of first phase  72 . 
     In addition, a pulse duty factor of the pulse width modulation which takes place in second phase  74  may be changed. It is thus possible to change the time curve of current  60  virtually arbitrarily, and thus, to optimize the switching characteristic of fuel supply control valve  22 . At a point in time t3 following point in time t2, the activation, and thus the energization, of solenoid  42  is terminated. Armature  44  once again reaches resting seat  43  at a subsequent point in time t4. 
     The activation of electrical actuating device  20  may take place in various ways. For example, during first phase  72 , electrical actuating device  20  may be activated with a monotonically increasing curve of current  60 , or with a first regulatable current  60 . Likewise, during second phase  74 , electrical actuating device  20  may be activated in the manner of a pulse width modulation, or may be activated with a second regulatable current. In general, an average current  60  in second phase  74  is less than in first phase  72 . In addition, a third phase (not illustrated) following second phase  74  may be provided in which electrical actuating device  20  is activated or energized with the aid of a pulse width modulation or a third regulatable current  60 . An average current  60  is generally higher in the third phase than in second phase  74 . 
     For ascertaining a limiting case, described in greater detail below, the lengths of the three phases and/or the currents flowing in the particular phases may be individually changed. 
       FIG. 4  shows two current curves  76  and  78  (current profiles, time curve of current  60 ) with currents  60  for activating electrical actuating device  20 , similar to the middle time diagram in  FIG. 3 . Current curve  76  characterizes a first activation of electrical actuating device  20 , in which valve element  54  is reliably switched from first position  45  into second position  47 , regardless of possible specimen variations. For example, current curve  76  corresponds to a time curve of current  60 , which may be set without using the method described in greater detail below in  FIG. 6 . 
     Current curve  78  characterizes a second activation of electrical actuating device  20 , in which valve element  54  is activated with a reduced (“second”) activation energy. In the present case, “activation energy” is generally understood to mean a respective time curve of current  60 . A first arrow  80  characterizes a point in time at which fuel supply control valve  22  opens, and a second arrow  82  characterizes a point in time at which fuel supply control valve  22  closes. 
     The second activation energy is a “first” activation energy which is increased by an offset value. The first activation energy corresponds to the above-mentioned limiting case in which valve element  54  only just or just no longer switches from first position  45  into second position  47 . The offset value is dimensioned in such a way that the second activation energy is much lower than an activation energy which corresponds to current curve  76 , although valve element  54  is able to switch into second position  47 , and the reliability of the switching is therefore not reduced. It is apparent that the second activation energy of current curve  78  is only approximately two-thirds of the activation energy of current curve  76 . 
       FIG. 5  shows a time diagram with time curves of a first operating noise  84  and a second operating noise  86  of electrical actuating device  20 . First operating noise  84  corresponds to current curve  76 , and second operating noise  86  corresponds to current curve  78  according to  FIG. 4 . It is apparent that second operating noise  86  is much lower than first operating noise  84 . 
       FIG. 6  shows a flow chart for a method for operating fuel system  10 . The present flow chart may preferably be processed with the aid of computer program  39 . The illustrated procedure begins in a start block  88 . 
     A check is made in a query block  90  as to whether a speed of the internal combustion engine is lower than a threshold value. If this is not the case, a branch is made back to the start of query block  90 . If this is the case, a branch is made to a subsequent block  92 . In block  92 , electrical actuating device  20  is activated in a first cycle in such a way that valve element  54  is reliably forced into second position  47 , for example using current curve  76 . 
     With the aid of query block  90 , a switch may be made between a first and a second type of operation of fuel supply control valve  22 . The first type of operation characterizes comparatively high speeds, using a “maximum current profile” for activating electrical actuating device  20 . The second type of operation characterizes comparatively low speeds, using a reduced current control (RECUR) of electrical actuating device  20 . For example, the second type of operation characterizes so-called “close to idling” speeds. 
     Electrical actuating device  20  is activated in a subsequent block  94  in at least one second cycle with an activation energy which gradually drops by a difference value. 
     A fuel pressure (“pressure”) in pressure accumulator  28  which is ascertained with the aid of pressure sensor  30  is evaluated in a subsequent block  96 . For example, a check is made as to whether the pressure and/or a pressure change and/or a rate of pressure change in pressure accumulator  28  has/have exceeded a threshold value. It is taken into account that when an instantaneous activation energy of electrical actuating device  20  is not, or no longer, sufficient to force valve element  54  from first position  45  into second position  47  during a delivery stroke, piston pump  24  carries out a so-called full delivery. This case of full delivery may be ascertained via a comparatively rapid rise in the pressure in pressure accumulator  28 . 
     A check is made in a subsequent query block  98  as to whether a pressure change which exceeds the threshold value has been ascertained in preceding block  96 . If this is not the case, the method is continued at the start of block  94 , the activation energy being further decreased in block  94 . However, if the threshold value has been exceeded, it is deduced that fuel supply control valve  22  is not, or no longer, open. This corresponds to a limiting case in which valve element  54  is only just or just no longer forced into second position  47 . Alternatively or additionally, instead of the fuel pressure or in addition to the fuel pressure, activation voltage  58  and/or current  60  may be evaluated in blocks  96  and  98  in order to ascertain the limiting case. 
     A branch is then made to a subsequent block  100  in which the first activation energy corresponding to the limiting case is ascertained. The above-described offset value is ascertained or predefined as a function of the fuel pressure in pressure accumulator  28  and a fuel temperature and an electrical resistance of electrical lines  35 , and is added to the first activation energy. The sum results in the second activation energy. The activation of electrical actuating device  20  is thus adapted to a specimen-dependent and/or speed-dependent switching characteristic of fuel supply control valve  22 . The first and the second activation energy, and optionally the speed and a predefinable time curve of the activation, are stored in data store  37  for subsequent activations of electrical actuating device  20 . This takes place using a characteristic map, for example. 
     Electrical actuating device  20  is subsequently activated with the second activation energy in a subsequent block  102 . However, it is also possible to ascertain the first and the second activation energy as well as the offset value as a function of the speed of the internal combustion engine. Fuel supply control valve  22  may thus also be activated as a function of the speed. The procedure illustrated in  FIG. 6  terminates in an end block  104 . 
     It is understood that the ascertainment of the described limiting case may correspondingly also take place in the reverse manner. Starting from an activation energy in which valve element  54  does not reliably switch into second position  47 , this activation energy is increased gradually until the limiting case is reached. In addition, the activation energy may also be gradually increased and decreased in alternation, as the result of which the limiting case may be ascertained more accurately if necessary.