Method for determining a value of a current

Abstract

A method for determining a value of a current, which is required for changing a switching state of a pressure control valve of a fuel delivery system, in which the current flowing through the pressure control valve is varied from a starting value up to a target value, and a time curve of the current is analyzed, the value required for changing the switching state being reached when the curve of the current has a change in slope, this change being detected via a first derivation over time of the current.

Claims

1. A method for determining a value of a current, which is required for changing a switching state of a pressure control valve of a fuel delivery system, the method comprising: varying the current flowing through the pressure control valve from a starting value up to a target value; and analyzing a time curve of the current, which time curve results from the varying, the analyzing including detecting for which value of the current the curve undergoes a change in slope and determining this current value as the value required for changing the switching state; wherein the change in slope is detected based on a first derivation over time of the current.

2. The method of claim 1, wherein the value required for changing the operating state is reached when the first derivation over time of the current has a plateau and/or a peak.

3. The method of claim 1, wherein the current is for a fuel delivery system of an internal combustion engine of a motor vehicle when the motor vehicle is in coasting mode.

4. The method of claim 1, wherein a change in the switching state of the pressure control valve includes an opening or a closing of the pressure control valve.

5. The method of claim 1, wherein the current flowing through the pressure control valve is increased or decreased from a starting value up to the target value for changing the switching state of the pressure control valve.

6. The method of claim 1, wherein the current is varied in steps or continuously.

7. The method of claim 1, wherein a value for the pressure at which the switching state of the pressure control valve is changed is assigned to the at least one value of the current, and wherein there is a characteristic of the pressure control valve which includes at least one pair of a value for the current and a value for the pressure.

8. A system to determine a value of a current, comprising: a control unit configured to determine the value of the current, which is required for changing a switching state of a pressure control valve of a fuel delivery system, wherein the control unit changes a current, which flows through the pressure control valve, from a starting value up to a target value and checks a resulting time curve of the current, wherein the control unit checks for which value of the current the curve of the current undergoes a change in slope and identifies this value as the value required for changing the switching state, and wherein the control unit detects this change in the slope based on a first derivation over time of the current.

9. The configuration of claim 8, further comprising: at least one pressure sensor which is configured as a component of the fuel delivery system, wherein the control unit assigns a value for a pressure, at which the pressure control valve changes the switching state and which is measured by the at least one pressure sensor, to the value of the current, and the control unit provides a characteristic of the pressure control valve, including at least one pair of a value for the current and the value for the pressure.

10. The configuration of claim 9, wherein the control unit internally corrects the characteristic of the pressure control valve.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 schematically shows diagrams used in a possible specific embodiment of the method according to the present invention.

(2) FIG. 2 schematically shows an example of a fuel delivery system and a specific embodiment of a configuration according to the present invention.

DETAILED DESCRIPTION

(3) The present invention is schematically shown in the drawings on the basis of specific embodiments and is described in greater detail below with reference to the drawings.

(4) The figures are described comprehensively and in general, using the same reference numerals to denote the same components.

(5) Each of the diagrams shown in FIG. 1 has an abscissa 1, along which a time is plotted in seconds. In the first diagram, values for an electric current in amperes are plotted along a left ordinate 3. Values for a first derivation over time of the current in A/s are plotted along a right ordinate 5 in the first diagram. In the second diagram, it is provided that a pressure in kbar is plotted along a left ordinate 7 and a derivation over time of the pressure in kbar/s is plotted along a right ordinate 9.

(6) In addition, the first diagram in FIG. 1 includes a time curve 11 of a current flowing through a pressure control valve of a fuel delivery system. An injection system of an internal combustion engine and thus cylinders of the internal combustion engine are supplied with fuel via this fuel delivery system.

(7) It should be pointed out here that the value of a pressure of the fuel, whose curve 13 is depicted in the second diagram, is not too high. It is provided here that an opening force of the pressure control valve which is caused by the pressure of the fuel is compensated by a closing force of the pressure control valve, which is provided by the current flowing through a coil of the pressure control valve. Alternatively, it is possible for the closing force to be supplied by a spring of the pressure control valve and for the opening force to be supplied by the coil through which the current flows. The opening force of the pressure control valve is the greater the higher the current.

(8) For carrying out a specific embodiment of the method according to the present invention, a value of the current, originating from a control unit and provided to the pressure control valve, is lowered to a target value from a starting value for changing a switching state of the pressure control valve, namely here for opening the pressure control valve. A time curve 11 of the current is detected by the control unit here.

(9) In addition, a first derivation over time 15 of the current is calculated by the control unit and is also detected.

(10) The first diagram therefore shows that the current, which is initially largely constant, is reduced sharply after about 0.5 second. It is provided that the starting value, i.e., the initial value, of the current is high enough to keep the pressure control valve closed at an instantaneously prevailing pressure of the fuel. As soon as the current, which is reduced from the starting value, has reached a value at which the pressure control valve is opened at an opening point in time 17, which is greater than 0.5 second, curve 11 of the current undergoes a change in slope. The change in slope of curve 11 of the current may be detected via a first derivation over time 15 of the current, for example, a feature in the course of first derivation over time 15. In the present specific embodiment, the first derivation over time 15 of the current, as shown by the first diagram, has a peak when the pressure control valve is opened on reaching a sufficiently reduced current. Alternatively or additionally, derivation 15 has a plateau at opening point in time 17. Opening point in time 17 of the pressure control valve is established by this value, which may be determined by analyzing the course of first derivation over time 15 of the current.

(11) The second diagram in FIG. 1 also shows a first derivation over time 19 of the pressure of the fuel in addition to the pressure of the fuel. A course of first derivation over time 19 of the pressure indicates that this value also changes greatly on opening 17 of the pressure control valve.

(12) In general, a value of the current, which is required for changing a switching state of a pressure control valve of a fuel delivery system, may be determined by this method. The current flowing through the pressure control valve changes in the direction of a target value from a starting value and a time curve of the current is analyzed, the value required for changing the switching state being reached when curve 11 of the current undergoes a change in slope, this change being detected via a first derivation over time 15 of the current.

(13) A change in the switching state of the pressure control valve may include an opening of the pressure control valve, as depicted in the diagrams in FIG. 1 as an example, during which the current flowing through the pressure control valve is reduced from a starting value to a smaller target value. However, it is also possible for the pressure control valve to be closed by reducing the current, depending on the type and/or operating mode of the valve. Again in this case, the change in the switching state of a corresponding pressure control valve is detected by a change in the first derivation of the current.

(14) Alternatively, a change in the switching state of the pressure control valve may include a closing of the pressure control valve during which the current flowing through the pressure control valve is increased from a starting value up to the larger target value.

(15) In this case, the starting value or the initial value of the current is low enough so that the pressure control valve is open at an instantaneously prevailing pressure of the fuel. As soon as the current, which is increased starting from the starting value, has reached a value at a closing point in time at which the pressure control valve is closed, the curve of the current also undergoes a change in slope. Here again, the change in slope in the curve of the current may also be detected via the first derivation over time of the current, for example, a feature in the characteristic of the first derivation over time, the first derivation over time also having a peak and/or a plateau when the pressure control valve is closed on reaching a sufficiently elevated current. The closing point in time of the pressure control valve is established by this value, which may be determined by analyzing the course of the first derivation over time of the current.

(16) In addition, depending on the operating mode and/or the type of pressure control valve, it is possible to open it by increasing the current from a starting value up to a target value. An opening point in time of the pressure control valve is also demonstrated in this case based on a change in the slope of the curve of the current, which is also indicated by a peak and/or a plateau as a feature in the course of the first derivation over time of the current.

(17) For carrying out the method, the current may be varied continuously or in steps, i.e., increased or decreased.

(18) FIG. 2 schematically shows an example of a fuel delivery system 20, which is configured to supply fuel to cylinders of an internal combustion engine. In detail, fuel delivery system 20 includes a tank 24 for storing the fuel, a first electronic fuel pump configured as a low-pressure pump 26, a fuel filter 28, a metering unit 30, a second electronic fuel pump which is configured as a high pressure pump 32, a fuel accumulator 34, which is also known as a common rail, a pressure sensor 36 and a pressure control valve 38. The aforementioned components of fuel delivery system 20 are interconnected via fuel lines.

(19) For operating fuel delivery system 20, fuel is delivered from tank 24 via low-pressure pump 26, fuel filter 28, metering unit 30 and high-pressure pump 32 to fuel accumulator 34, where the fuel is stored under pressure. Fuel accumulator 34 is connected to fuel injectors 40, each injector 40 being assigned to a cylinder of the internal combustion engine. If the pressure inside fuel delivery system 20 is too high, fuel may be discharged through pressure control valve 38 and returned to tank 24. A value at which pressure control valve 38 is opened is established by a current which flows through a coil of pressure control valve 38.

(20) FIG. 2 also shows a control unit 42 as a component of a configuration 44 according to the present invention. Control unit 42 is connected to the components of fuel delivery system 20 and exchanges signals with it, these signals being sensor signals and actuator signals, so that control unit 42 is able to monitor, i.e., control and/or regulate, an operation of the components of fuel delivery system 20.

(21) Control unit 42 is configured for determining a value of the current, which is required for changing a switching state, i.e., for opening or closing pressure control valve 38. The current flowing through pressure control valve 38 is therefore varied by control unit 42 from a starting value up to a target value, and a curve of the current is analyzed and thus monitored by control unit 42. Control unit 42 checks for which value of the current the curve of the current has a change in slope, this value being identified by control unit 42 as the value required for opening or closing. The change in slope may be detected by control unit 42 by analyzing and/or checking the first derivation over time of the curve of the current and is usually reached when the first derivation over time of the current has a certain feature, for example, a significant peak and/or a significant plateau. The current may be increased or decreased for opening, depending on the type and/or operating mode of pressure control valve 38 as a function of the provided change in the switching state. It is also possible to increase or decrease the current for closing pressure control valve 38, depending on its type and/or operating mode.

(22) In addition, a value for the pressure at which pressure control valve 38 is opened or closed and which is measured by at least one pressure sensor 36 is assigned by control unit 42 to at least one value of the current. The control unit here supplies a characteristic of pressure control valve 38, which includes at least one pair of a value for the current and a value for the pressure, control unit 42 internally correcting the characteristic of pressure control valve 38. This characteristic may be supplemented by new pairs, each having a value for the current and a value for the pressure. Already existing pairs may be replaced by new pairs. The characteristic is usually updated during operation.

(23) A method for determining the value of the current for opening or closing pressure control valve 38 may be carried out for a fuel delivery system of an internal combustion engine of a motor vehicle if the motor vehicle is in coasting mode. The opening or closing of pressure control valve 38 may be delayed to optimize a guidance behavior of a high-pressure controller of the fuel delivery system.

(24) The method described here may be used in vehicles having a diesel engine and a common rail system having a pressure control valve 38 and a metering unit 30.

(25) Regardless of the type and/or operating mode of pressure control valve 38, a change in the switching state of pressure control valve 38 is induced by a change in current from the starting value up to the target value of the current, the current being either decreased or increased; this pressure control valve 38 may be either opened or closed. The value of the current to be determined as part of the method described here, which causes the change in the switching state, is determined in all possible cases with regard to the type and/or operating mode of pressure control valve 38 on the basis of a change in the curve of the current, which is either increased or decreased, this change being detected by a feature in the first derivation over time of the current. It is possible here to either open or close a pressure control valve 38, depending on the type and/or operating mode by a decrease in the current or to either open or close the valve by an increase in the current.