Abstract:
A method for controlling a fuel injection system ( 10 ) of an internal combustion engine. Including a high-pressure pump ( 16 ) associated with a quantity controlling valve ( 15 ) having a solenoid valve ( 22 ) electromagnetically actuatable by a coil ( 21 ) for supplying fuel, the quantity control valve ( 15 ) controlling the quantity of fuel supplied by the high-pressure pump ( 16 ) and the coil ( 21 ) of the solenoid valve ( 22 ) having a first current value applied thereto, in order to close the same for supplying fuel to the high-pressure pump ( 16 ), the first current value being reduced to a second current value when the solenoid valve is closing ( 22 ), such that the radiation of audible sound arising from the closing of the solenoid valve ( 22 ) is at least partially reduced.

Description:
This application is a National Stage Application of PCT/EP2008/059400, filed 17 Jul. 2008, which claims benefit of Serial No. 10 2007 035 316.4, filed 27 Jul. 2007 in Germany and which applications are incorporated herein by reference. To the extent appropriate, a claim of priority in made to each of the above disclosed applications. 
     TECHNICAL FIELD 
     The present invention relates to a method for controlling a fuel injection system of an internal combustion engine, the fuel injection system comprising a high-pressure pump associated with a quantity controlling valve having a solenoid valve electromagnetically actuatable by a coil for supplying the fuel, the quantity control valve controlling the quantity of fuel supplied by the high-pressure pump and the coil of the solenoid valve having a first current value applied thereto, in order to close the same for supplying fuel to the high-pressure pump. 
     A method for controlling a fuel injection system with a quantity control valve is already known from the technical field. Such a quantity control valve is implemented as a rule as a solenoid valve electromagnetically acuatable by a coil and having a magnetic armature and associated displacement limiting stops. The solenoid valve is open when no power is present. In order to close the solenoid valve, the coil is activated with a constant voltage—battery voltage—the current in the coil increasing in a characteristic manner. After switching off the voltage, the current drops in turn in a characteristic manner, and the solenoid valve opens shortly after the current has dropped. The time between switching off the voltage at the coil and the opening of the valve is designated as discharging time. 
     In order to reduce the discharging time, the voltage applied to the coil can be reduced when the solenoid valve is closing and before the same achieves a corresponding end position, i.e. before the magnetic armature touches against the displacement limiting stops. In so doing, the current in the coil and consequently also the magnetic force are rapidly increased by the voltage which was initially applied in order to achieve a quick onset of movement of the magnetic armature. An unnecessary increase in the current in the coil is then avoided by reducing the applied voltage. This reduction in voltage can take place both prior to as well as after a specified force value has been achieved, whereat the magnetic armature begins to move. It is important in this case that a reliable attraction of the magnetic armature is assured. 
     In the event that the current supply to the solenoid valve is set too low during the operation of such a fuel injection system, its actuation time can possibly be lengthened to such an extent that the magnetic valve does not completely close in a provided actuation time, and as a result a sufficient high pressure cannot be built up in the high-pressure pump. In order to avoid this, the current supply is defined in a way that a closing of the solenoid valve is always assured. If the defined current supply is, however, frequently set so high that the actuation behavior of the solenoid valve is relatively high and as a result a correspondingly high speed at impact of the magnetic armature against the displacement limiting stops occurs, a hard striking of the magnetic armature against the displacement limiting stops then results. In so doing, an audible sound arises, which is radiated by the internal combustion engine and which can be perceived by the operator to be unpleasant and disturbing. 
     SUMMARY 
     It is therefore the task of the present invention to provide a method and a device, which allow for a reduction in the audible sound when solenoid valves of a quantity control valve are actuated. 
     This problem is solved by a method for controlling a fuel injection system of an internal combustion engine. The fuel injection system comprises a high-pressure pump, which is associated with a quantity control valve having a solenoid valve electromagnetically acuatable by a coil for supplying fuel to said pump. The quantity control valve controls the quantity of fuel supplied by the high-pressure pump. The coil of the solenoid valve has a first current value applied thereto in order to close the same for supplying fuel to the high-pressure pump. When the solenoid valve is closing, the first current value is reduced to a second current value in such a way that a radiation of audible sound arising from the closing of the solenoid valve during operation of the internal combustion engine is at least partially reduced. 
     The invention consequently allows for a reduction in the audible sound during the operation of the internal combustion engine so that said engine is subjectively perceived to be more pleasant and quieter. 
     According to the invention, the second current value corresponds to a minimum current value, with which a complete closing of the solenoid valve can be achieved during the operation of the internal combustion engine. 
     A maximum reduction in the audible sound can consequently be achieved. 
     The high-pressure pump is connected to a pressure reservoir, whereat at least one fuel injection valve is attached. Here an actual pressure value is compared with an associated nominal pressure value. In order to determine the minimum current value, a malfunction current value is preferably ascertained, whereat the deviation of the actual pressure value from the nominal pressure value exceeds a predetermined threshold value, the ascertained malfunction current value being increased by a predetermined safety offset. 
     A complete closing of the solenoid valve is assured by the increase in the ascertained malfunction current value by the predetermined safety offset. 
     A nominal pressure value required for operation can alternatively be predetermined for the high-pressure pump, which is connected to a pressure reservoir, whereat at least one fuel injection valve is attached, from an associated pressure controller, the minimum current value being determined as a function of an increase in the nominal pressure value during the operation of the internal combustion engine. In so doing, a malfunction current value, whereat the increase in the nominal pressure value exceeds a predetermined threshold value, is ascertained for determining the minimum current value, the ascertained malfunction value being increased by a predetermined safety offset. 
     The invention can therefore be implemented using already available components and elements, a complete closing of the solenoid valve being assured by the increase in the ascertained malfunction current value by the predetermined safety offset. 
     According to the invention, the solenoid valve has a magnetic armature, which is drawn against associated displacement limiting stops in order to close the solenoid valve, the audible sound occurring by the striking of the magnetic armature against the displacement limiting stops. At this juncture, an actuation behavior of the solenoid valve is decelerated by reducing the first current value to a second current value in order to reduce a corresponding speed at impact of the magnetic armature against the displacement limiting stops. 
     By reducing the speed at impact, the audible sound produced when the magnetic armature impacts against the displacement limiting stops is reduced. 
     The problem mentioned at the beginning of the application is also solved by a computer program for carrying out a method for controlling a fuel injection system of an internal combustion engine, the fuel injection system comprising a high-pressure pump associated with a quantity control valve having a solenoid valve electromagnetically actuatable by a coil for supplying fuel, the quantity control valve controlling the quantity of fuel supplied by the high-pressure pump and the coil of the solenoid valve having a first current value applied thereto in order to close the same for supplying fuel to the high-pressure pump. The computer program reduces the first current value to a second current value when the solenoid valve is closing, such that a radiation of audible sound arising from the closing of the solenoid valve during operation of the internal combustion engine is at least partially reduced. 
     The problem mentioned at the beginning of the application is also solved by an internal combustion engine with a fuel injection system comprising a high-pressure pump associated with a quantity control valve having a solenoid valve electromagnetically actuatable by a coil for supplying fuel, the quantity of fuel supplied by the high-pressure pump being controllable by the quantity control valve by means of supplying the coil of the solenoid valve with a first current value in order to close the same for supplying fuel to the high-pressure pump. The first current value can be reduced to a second current value when the solenoid valve is closing in order to at least partially reduce a radiation of audible sound arising from the closing of the solenoid valve during operation of the internal combustion engine. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic depiction of a fuel injection system of an internal combustion engine with a high-pressure pump and a quantity control valve; 
         FIG. 2  is a schematic depiction of different functional states of the high-pressure pump from  FIG. 1  with an associated time diagram; 
         FIG. 3  is a flow chart of a method for controlling the quantity control valve from  FIG. 1 , 
         FIG. 4  is a schematic depiction of the temporal progression of the lift of the solenoid valve from  FIG. 1  and the activation voltage required for this purpose, respectively the current supply during activation according to the invention; 
         FIG. 5  is a schematic depiction of the temporal progression of the lift of the solenoid valve from  FIG. 1  and the activation voltage required for this purpose, respectively the current supply during a conventional activation; 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a schematic depiction of a fuel injection system  10  of an internal combustion engine. This comprises an electric fuel pump  11 , with which fuel is conveyed from the tank  12  and is pumped further across a fuel filter  13 . The fuel pump  11  is suited for the purpose of producing low pressure in the system. A low pressure regulator  14 , which is connected to the outlet of the fuel filter  13 , is provided for the open-loop and/or closed-loop control of this low pressure. Fuel can be conveyed again back to the fuel tank  12  via said regulator  14 . Furthermore, a series connection comprising a quantity control valve  15  and a mechanical high-pressure pump  16  is attached at the outlet of the fuel filter  13 . The outlet of the high-pressure pump  16  is led back to the inlet of the quantity control valve  15  via a pressure relief valve 17 . The outlet of the high-pressure pump  16  is furthermore connected to a pressure reservoir  18 , whereat a plurality of injection valves  19  is attached. A pressure regulator  33  specifies a nominal pressure value to be produced by the high-pressure pump  16  for the pressure reservoir  18 . The pressure reservoir  18  is also often designated as the rail or common rail. Furthermore, a pressure sensor  20  is attached to the pressure reservoir  18 . 
     In the present example, the fuel injection system  10  depicted in  FIG. 1  serves the purpose of supplying the injection valves  19  of a four cylinder internal combustion engine with sufficient fuel and the necessary fuel pressure so that a reliable injection of fuel and a reliable operation of the internal combustion engine is assured. 
     The functionality of the quantity control valve  15  and the high-pressure pump  16  is depicted in detail in  FIG. 2 . The quantity control valve  15  is constructed as a normally open solenoid valve  22  and has a coil  21 . The solenoid valve can be closed or opened by applying or switching off an electrical current, respectively an electrical voltage, via said coil  21 . The high-pressure pump  16  has a piston  23 , which is actuated by a cam  24  of the internal combustion engine. Furthermore, the high-pressure pump  16  is equipped with a valve  25 . A conveying chamber  26  of the high-pressure pump  16  is located between the solenoid valve  22 , the piston  23  and the valve  25 . 
     With the solenoid valve  22 , the conveying chamber  26  can be separated from a fuel feed by the electric fuel pump  11  and thereby from the low pressure. With the valve  25 , the conveying chamber  26  can be separated from the pressure reservoir  18  and thereby from the high pressure. 
     The solenoid valve  22  is open and the valve  25  is closed in the initial state as it is depicted in  FIG. 2 . The open solenoid valve  22  corresponds to the currentless state of the coil  21 . The valve  25  is held closed by the pressure of a spring or something similar. 
     In the diagram on the left of  FIG. 2 , the intake stroke of the high-pressure pump  16  is depicted. When the cam  24  rotates in the direction of the arrow  27 , the piston  23  moves in the direction of the arrow  28 . As a result of the solenoid valve  22  being open, fuel, which has been supplied by the electric fuel pump  11 , consequently flows into the conveying chamber  26 . 
     In the diagram in the middle of  FIG. 2 , the delivery stroke of the high-pressure pump  16  is shown, the coil  21 , however, being still without current and the solenoid  22  thereby still being open. As a result of the rotational movements of the cam  24 , the piston  23  moves in the direction of the arrow  29 . As a result of the solenoid valve  22  being open, fuel is for this reason conveyed out of the conveying chamber  26  and back in the direction of the electric fuel pump  11 . This fuel then travels back into the fuel tank  12  via the low pressure regulator  14 . 
     In the diagram on the right of  FIG. 2 , the delivery stroke of the high-pressure pump  16  is further shown as in the middle diagram. In contrast to the middle diagram, the coil  21  is now energized and the solenoid valve  22  is thereby closed. This results in pressure being built up in the conveying chamber  26  by means of the further stroke movement of the piston  23 . When the pressure is achieved, which prevails in the pressure reservoir  18 , the valve  25  is opened and the residual quantity is conveyed into the pressure reservoir. 
     The quantity of the fuel supplied to the pressure reservoir  18  depends upon when the solenoid valve  22  enters into its closed state. The earlier the solenoid valve is closed, the more fuel is conveyed into the pressure reservoir  18  via the valve  25 . This is depicted in  FIG. 2  by a region B which is designated by an arrow. 
     As soon as the piston  23  in the diagram on the right of  FIG. 2  has reached its point of maximum travel, no further fuel can be conveyed by the piston  23  into the pressure reservoir  18  via the valve  25 . The valve  25  closes. Furthermore, the coil  21  is again deenergized so that the solenoid valve opens again. As a reaction to that, the piston, which now moves according to the diagram on the left of  FIG. 2  in the direction of the arrow  28 , again draws fuel conveyed by the electric fuel pump into the conveying chamber  26 . 
     A method for controlling the fuel injection system  10  of  FIG. 1  according to one embodiment of the invention with reference to  FIGS. 3 and 4  will be described in detail below. 
       FIG. 3  shows a flow chart of a method  300  for controlling the fuel injection system  10  of the internal combustion engine of  FIGS. 1 and 2  to reduce the audible sound, which arises from switching the quantity control valve  15  during the operation of the internal combustion engine. According to a preferred embodiment of the invention, the method  300  is implemented as a computer program which can be executed by a suitable open-loop and closed-loop control device, which is already provided in the internal combustion engine. The invention can therefore be simply and cost effectively implemented with components which are already present in the internal combustion engine. 
     In the following description of the method according to the invention, a detailed explanation of the procedural steps known in the technical field is foregone. 
     The method  300  begins at step S 301  with the supply of current to the coil  21  of the solenoid valve  22 . For this purpose, an activation voltage which is present at the coil  21  can be switched off so that a corresponding current is induced in the coil  21 . 
     In step S 302  the coil current of the coil is measured. The measured coil current is then compared with a predetermined adaptation current supply initial value. This can, for example, be determined with the aid of a suitable characteristic curve. As long as the measured coil current is smaller than the predetermined adaptation current supply initial value, the method  300  proceeds with the measurement of the coil current and the comparison of the measured coil current with the predetermined adaptation current supply initial value according to step S 302 . If the measured coil current is equal to or greater than the predetermined adaptation current supply initial value, the method  300  proceeds to step S 303 . 
     In step S 303  the current supply to the coil  21  starting at the predetermined adaptation current supply initial value is dropped to a reduced current value. According to one embodiment of the invention, this drop takes place in the form of a decrementation, for example by switching on the activation voltage again which is present at the coil  21 . 
     In step S 304  a respective, current actual pressure value of the pressure reservoir  18  is determined, for example by the pressure sensor  20 . In step S 305  a determination is made, as is explained below, whether the current actual pressure value of the pressure reservoir  18  has dropped dramatically. In the event that this is not the case, the method  300  returns to step S 303 , where the present current value for the current supply to the coil  21  is again decremented. A plurality of consecutive decrementations can accordingly be carried out, for example by a repeated switching-on and off of the activation voltage present at the coil  21  relative to a predetermined PWM duty cycle. 
     In order to determine in step S 305  whether the current actual pressure value of the pressure reservoir  18  has dramatically dropped, the actual pressure value is according to the invention compared with a nominal pressure value, which is specified by the pressure regulator  33 . If the deviation of the actual pressure value from the nominal pressure value exceeds a predetermined threshold value, it is thereby assumed that the actual pressure value has dropped, whereupon the method  300  proceeds to step S 306 . As an alternative to this, a dramatic drop in the actual pressure value can then also be assumed if the pressure regulator  33  increases the nominal pressure value to such an extent that this increase exceeds a predetermined increase threshold value. 
     It is assumed in step S 306  that in the case that the current value is reduced, with which the coil  21  is supplied with current, a complete closing of the solenoid valve  22  is no longer assured if it can be assumed that the current actual pressure value of the pressure reservoir  18  has dropped dramatically. In the event that the solenoid valve  22  no longer completely closes, the high-pressure pump  16  breaks down, i.e. the fuel conveyance by the high-pressure pump  16  is at least limited to the extent that a sufficient high pressure can no longer be built up in the pressure reservoir  18 . Therefore, the present current value supplying current to the coil  21  at this point in time, respectively actual current supply value, is also subsequently referred to as the “breakdown current value”. 
     In order to assure during subsequent operation of the internal combustion engine that the solenoid valve  22  reliably and completely closes in each case, the ascertained breakdown current value is then increased in step S 306  by a predetermined safety offset. In so doing, a minimum current value is determined, with which the coil  21  of the solenoid valve  22  is to be supplied with current during the operation of the internal combustion engine in order to reliably and completely close the solenoid valve  22 . 
     During subsequent operation of the internal combustion engine, the current supply to the solenoid valve  22  can consequently be reduced to this minimum current value when an appropriate closing procedure in each case occurs upon achieving the adaptation current supply initial value. Because of this, the actuation time of the solenoid valve  22  is respectively maximized so that the speed at impact of the magnetic armature  31  against the displacement limiting stops  32  is minimized, and as a result the audible sound produced in this connection can be reduced. 
       FIG. 4  shows a diagram  400 , which depicts a temporal course  410  of an activation voltage U, a temporal course of a temporal current profile  420  of the current I ensuing from said course  410  as well as a corresponding temporal course  430  of a valve lift H of the quantity control valve  15  from  FIG. 1 , which was brought about by the current profile  420 , respectively a valve lift H of the solenoid valve  22  from  FIG. 2  of the fuel injection system  10  from  FIG. 1 . The diagram  400  illustrates an activation of the solenoid valve  22  according to one embodiment of the invention. Said activation begins at a point in time  405 , whereat the activation voltage U Bat  present at the coil  21  of the solenoid valve  22  (as described above in reference to step S 301  of  FIG. 3 ) is switched off for an actuation pulse length  412 . As a result, the current in the coil  21  increases up to a current value  421  up until the point in time  425 . 
     In the present example of embodiment, the current value  421  represents the adaptation current supply initial value according to step S 302  of  FIG. 3 . The adaptation according to the invention accordingly begins at the point in time  424  as described above in reference to step S 303  of  FIG. 3 . The switching-on and off of the activation voltage relative to a predetermined PWM duty cycle  414  is depicted here as in  FIG. 4 , the adaptation current supply initial value  421  being lowered to a reduced current value  422  up to a point in time  433 . An actuation phase  411  required for closing the solenoid valve  22  is concluded at the point in time  433 , and the solenoid valve  22  closes so that the point in time  433  is also referred to as the closing time point. As can be seen from the temporal course  420 , the reduced current value  422  is then increased by a predetermined safety offset in order to assure a complete closing of the solenoid valve  22 . 
     After the closing of the solenoid valve  22 , the same is held closed for a predetermined holding phase  413 , whereupon the activation voltage is again set to U Bat  up to the next ensuing closing procedure. The time period between the closing of the solenoid valve  22  and the expiration of the holding phase  413  is also denoted by a holding angle  415 . The current supply to the solenoid valve  22  consequently drops again so that the same reopens. 
     As can be seen in  FIG. 4 , a relatively long actuation phase  411 , respectively dead time  432 , is implemented during the activation of the solenoid valve  22  according to the invention. In so doing, the speed at impact of the magnetic armature  31  against the displacement limiting stops  32  is reduced and consequently the audible sound produced in this connection is significantly reduced. 
       FIG. 5  shows a diagram  500 , which for the purpose of comparison depicts a temporal course  510  of an activation voltage U, a temporal course of a temporal current profile  520  of the current I ensuing from said course  510  as well as a corresponding temporal course  530  of a valve lift H of the quantity control valve  15  from  FIG. 1 , which was brought about by the current profile  520 , respectively a valve lift H of the solenoid valve  22  from  FIG. 2  of the fuel injection system  10  from  FIG. 1  during an activation according to the technical field. As can be seen from  FIG. 5 , a peak current value  522  in the coil  21 , which is larger than the current values achieved according to the invention, is brought about in this instance by a greater actuation pulse length  512  in a shorter actuation phase  511 . In so doing, a shorter dead time  532  and consequently a correspondingly earlier closing time point  523  are brought about while the speed at impact is greater so that the magnetic armature  31  strikes harder and correspondingly louder, respectively more audibly, against the displacement limiting stops  32 .