Abstract:
A method for controlling and/or regulating a d.c. converter for at least two electromagnetic valves of an internal combustion engine of a motor vehicle is provided. A current generated by the d.c. converter is supplied to each valve. A determination is made as to when the total currents supplied to the valves constitute a high load for the d.c. converter. If this is the case, the d.c. converter is influenced in the sense of better processing of the high load.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention is directed to a method for controlling and/or regulating a d.c. converter for at least two electromagnetic valves of an internal combustion engine in which each valve is supplied with a current generated by the d.c. converter. The present invention also relates to a corresponding device for controlling and/or regulating a d.c. converter for at least two electromagnetic valves.  
       BACKGROUND INFORMATION  
       [0002]     It is known that a plurality of electromagnetic valves may be supplied with current by a d.c. converter via an output stage. In this context, it is possible for overlapping currents for the different valves to result in a high load for the d.c. converter as a whole. The d.c. converter must be designed for this high load, which is associated with increased expenditure under some circumstances.  
       SUMMARY OF THE INVENTION  
       [0003]     The object of the present invention is to provide a method in which the expenditure for processing a high load of the d.c. converter is reduced.  
         [0004]     This object is achieved with the method according to the present invention by determining when the total currents supplied to the valves represent a high load for the d.c. converter, and if this is the case, by adapting the d.c. converter for improved processing of the high load. The present invention also provides a corresponding device.  
         [0005]     The d.c. converter is set to the high load using the present invention. Thus, the d.c. converter is capable of better processing this high load. This in turn entails the advantage that the d.c. converter need no longer be designed on the basis of the high load but instead may be designed by taking into account the better processing according to the present invention. In particular, it is possible to select the output capacitor of the d.c. converter to be smaller than would be necessary to match a high load.  
         [0006]     In an advantageous further refinement of the present invention, the output voltage of the d.c. converter is increased when there is a high load. The output voltage may be controlled and/or regulated to a setpoint value and the n setpoint value may be increased.  
         [0007]     This measure achieves the result that the high load of the d.c. converter results in a lower dip in the output voltage. In particular, as already mentioned, the smaller dip in the output voltage allows a smaller output capacitor of the d.c. converter to be used.  
         [0008]     It is particularly advantageous if the increase in the output voltage and/or the setpoint value is already performed before the high load occurs. Thus the d.c. converter is prepared for the high load. In this case, the output voltage already increases to the full extent when the high load occurs and is thus effective.  
         [0009]     A further implementation of the present invention includes a computer program having program commands suitable for execution of the method according to the present invention when the computer program runs on a computer. Accordingly, the present invention is implemented by a digital storage medium including a computer program having program commands suitable for executing the method according to the present invention.  
       BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  shows a schematic block diagram of an exemplary embodiment of a device according to the present invention for controlling at least two electromagnetic valves of an internal combustion engine.  
         [0011]      FIG. 2  shows a schematic wiring diagram for one of the electromagnetic valves with the current flow in four successive time ranges.  
         [0012]      FIG. 3  shows a schematic time chart of the current across one of the electromagnetic valves in the four time ranges.  
         [0013]      FIGS. 4   a - 4   c show three schematic time charts of currents and voltages across, or at, the electromagnetic valves. 
     
    
     DETAILED DESCRIPTION  
       [0014]      FIG. 1  shows a device  10  for controlling at least two electromagnetic valves  11 ,  12 . Electromagnetic valves  11 ,  12  are provided for use in an internal combustion engine in a motor vehicle in particular. For example, electromagnetic valves  11 ,  12  may be provided in conjunction with an electrohydraulic valve control for the intake and exhaust valves of the internal combustion engine. In this case, a hydraulic system is controlled via electromagnetic valves  11 ,  12 , the intake and exhaust valves of the internal combustion engine being able to be opened and closed using the hydraulic system.  
         [0015]     It is point ed out here explicitly that device  10  may be used not only for two valves  11 ,  12  depicted here, but may also be used for any number of valves through appropriate expansions. It is thus possible to have a total of  32  solenoid valves for controlling the intake and exhaust valves of the internal combustion engine in the case of an engine having four cylinders.  
         [0016]     Two d.c. converters  13 ,  14 , which together form a converter  17 , are provided for supplying power to valves  11 ,  12 . Both d.c. converters  13 ,  14  and thus converter  17  include control means and/or regulating means for maintaining the generated output voltages at a predetermined setpoint level.  
         [0017]     D.c. converter  13  is suitable for generating a booster current on an electric line  15 . Accordingly, d.c. converter  14  is suitable for generating a holding current on an electric line  16 . The booster current is greater than the holding current.  
         [0018]     An output stage  20 , which controls the current flow across valves  11 ,  12 , is provided between d.c. converters  13 ,  14  and valves  11 ,  12 . This control takes place via a control unit  19 . The function of output stage  20 , its control, and the generated current flow across valve  11  is explained in greater detail below in connection with  FIG. 2 . The explanation given there also applies accordingly to the current flow across valve  12  and the current flow across any additional valve.  
         [0019]      FIG. 2  shows lines  15 ,  16  coming from two d.c. converters  13 ,  14 . Line  16  is connected via a diode D 1 , which is connected in the flow direction, to one of the two terminals of electromagnetic valve  11 . The other terminal of electromagnetic valve  11  is connected via a diode D 2 , which is also connected in the flow direction, to line  15 . The cathodes of both diodes D 1 , D 2  are interconnected via a switch S 1 . The anode of diode D 2  is connected to ground via a switch S 2 .  
         [0020]     Depending on the switch positions of two switches S 1 , S 2 , there is a different current flow across valve  11 . Four different switch positions resulting in four different current flows in four successive time ranges a, b, c, d may be set using two switches S 1 , S 2 . Control unit  19  as already mentioned controls the positions of two switches S 1 , S 2 .  
         [0021]      FIG. 3  shows current I MV  across electromagnetic valve  11  as a function of time. In particular,  FIG. 3  shows four time ranges a, b, c, d resulting from the four adjustable switch positions of two switches S 1 , S 2 .  
         [0022]     In first time range a, both switches S 1 , S 2  are closed. This yields current flow a, as shown in  FIG. 2  and designated accordingly as “a.” The booster current generated by d.c. converter  13  flows across valve  11 . This current I MV  increases to a final value according to  FIG. 3  and is provided to adjust valve  11  into a preselected end position in any case.  
         [0023]     In second time range b, which follows time range a, switch S 1  is closed and switch S 2  is opened. This yields a current flow as shown in  FIG. 2  and designated accordingly as “b.” This current flow is known as free-running. This means that at least a portion of the electric energy contained in electromagnetic valve  11  is dissipated via this free-running state. Accordingly, current I MV  declines in time range b according to  FIG. 3 .  
         [0024]     Switch S 1  is opened in time range c and switch S 2  is closed. This yields a current flow like that shown in  FIG. 2 , where it is designated accordingly as “c.” The holding current generated by d.c. converter  14  in time range c is sent to valve  11 . This holding current is selected so that the end position reached by valve  11  on the basis of the booster current does not change.  
         [0025]     Both switches S 1 , S 2  are opened in time range d, which follows time range c. This yields a current flow like that shown in  FIG. 2  and designated accordingly as “d.” This current flow represents quenching of electromagnetic valve  11 . This means that the energy in electromagnetic valve  11  is dissipated completely to 0. Current I MV  then issuing from valve  11  flows across diode D 2  to d.c. converter  13  in time range d.  
         [0026]      FIG. 4   a shows booster current I B  for connected valves  11 ,  12  generated by d.c. converter  13 , plotted as a function of time t.  
         [0027]     On the basis of two or more valves  11 ,  12  present here, it is possible for the booster currents of time ranges a of two or even more valves  11 ,  12  to overlap. Such overlap together with the resulting high booster current is designated by reference numeral  22  in  FIG. 4   a.    
         [0028]     High booster current  22  results in d.c. converter  13  being exposed to very high loads. The following is provided for better processing of these loads:  
         [0029]     Control unit  19  is connected to converter  17  via line  18 , in particular to d.c. converter  13 , which is responsible for the booster current. Control unit  19  determines when a high load has occurred due to overlapping booster currents. Control unit  19  is able to derive this from the provided triggerings of switches S 1 , S 2  of output stage  20 .  
         [0030]     Before a high load occurs, control unit  19  indicates the imminent high load to converter  17 , in particular d.c. converter  13 . This is accomplished with the help of a signal S, which is sent from control unit  19  via line  18  to converter  17 .  
         [0031]      FIG. 4   b  shows signal S plotted as a function of time t. It is apparent here that signal S is present during a period of time T, which extends from a point in time T 1  to a point in time T 2 . This is designated by reference numeral  23  in  FIG. 4   b . Period of time T corresponds approximately to the period of time during which high booster current  22  from  FIG. 4  is present.  
         [0032]      FIG. 4   c  shows output voltage U B  of d.c. converter  13  plotted as a function of time. As mentioned previously, this output voltage U B  is controlled and/or regulated to a predetermined setpoint value. The setpoint value is designated as U Bsetpoint  in  FIG. 4   c . Control and/or regulation of d.c. converter  13  is designed, for example, so that output voltage U B  of d.c. converter  13  varies in a tolerance range of ±10% around setpoint value U BS .  
         [0033]     As  FIG. 4   c shows, setpoint value U BS  of output voltage U B  of d.c. converter  13  is raised during period of time T. This is indicated with a dashed line in  FIG. 4   c  and labeled as  24 .  
         [0034]     As already mentioned, period of time T of  FIG. 4   b  begins shortly before the rise in high booster current  22  in  FIG. 4   a  after time T 1 . As a result, setpoint value U Bsetpoint  also increases just prior to the rise in high booster current  22 . This increase in setpoint value U Bsetpoint  also yields an increase in output voltage U B  of d.c. converter  13 , which is shown by a dashed line in  FIG. 4   c  and is designated by reference numeral  25 .  
         [0035]     After the point in time when booster current I B  (which is designated as  22  in  FIG. 4   a ) rises, d.c. converter  13  thus supplies an increased output voltage U B  (designated as  25 ). This yields the result that d.c. converter  13  is able to better process the high load associated with the rise in booster current I B .  
         [0036]     In particular, increased setpoint value U Bsetpoint  and resulting increased output voltage U B  result in the dip in this output voltage U B  due to high booster current I B  being lower than would be the case without the aforementioned increase. This is shown in  FIG. 4   c  on the basis of the curves designated by reference numerals  26 ,  27 . The curve resulting from the increase in setpoint value U Bsetpoint  is indicated by a dashed line and is designated by reference numeral  26 , while the curve that would result without the above-described increase in setpoint value U Bsetpoint  is designated by reference numeral  27 .  
         [0037]     Due to the smaller dip in output voltage U B  (designated as  26  in  FIG. 4   c ), it is possible to provide d.c. converter  13  with a lower output capacitance than would be necessary without the increase in setpoint value U Bsetpoint . It is likewise possible for the control and/or regulating means contained in converter  17  to take preventive measures on the basis of signal S, namely in particular on the basis of the rise in signal S at the beginning of period of time T and to do so as a preventive measure even before the occurrence of a system deviation to counteract the system deviation that would result on the basis of the high booster current. In particular, the control and/or regulating means may increase the output power of d.c. converter  13  as a preventive measure. Other emergency functions may be implemented via line  18  as follows:  
         [0038]     For example, if d.c. converter  14  fails and if this is detected by control unit  19  via measures not described more closely in the present case, control unit  19  may control and/or regulate remaining d.c. converter  13  so that it assumes the function of d.c. converter  14  and additionally generates the holding current. For example, the output voltage of d.c. converter  13  may be pulsed to thereby generate a corresponding holding current.  
         [0039]     In the inverse case, control unit  19  may control and/or regulate d.c. converter  14  so that it generates not only the holding current but also the booster current. In particular, control unit  19  may increase the setpoint value of the output voltage of d.c. converter  14 . In addition, it may be advisable for control unit  19  to trigger switches S 1 , S 2  at an earlier point in time for generating the booster current to thus compensate for possible deterioration of the tightening dynamics of valves  11 ,  12 .