Method and computer program for actuating a fuel injector

Abstract

A method actuates a fuel injector having a coil drive with a solenoid and a magnet armature. The magnet armature can be moved along a longitudinal axis by a magnetic field generated by the solenoid. In the method, an amplification voltage is applied to the solenoid at a predefined point in time to move the magnet armature from a closed position into an open position. The amplification voltage is made available by a voltage-regulated direct voltage transformer from a supply voltage. The direct voltage transformer has a storage capacitor for supporting the voltage made available at the output of the direct voltage transformer. The storage capacitor is charged to a pilot control voltage by the amplification voltage before the given point in time, with the result that the voltage present at the solenoid is higher than the amplification voltage at the predefined point in time.

Claims

1. A method for actuating a fuel injector having a coil drive with a solenoid and a magnet armature, wherein the magnet armature can be moved along a longitudinal axis by a magnetic field being generated by the solenoid, which comprises the steps of: applying an amplification voltage to the solenoid at a predefined point in time to move the magnet armature from a closed position into an open position, wherein the amplification voltage being made available by a voltage-regulated direct voltage transformer from a supply voltage which is lower in comparison than the amplification voltage, the voltage-regulated direct voltage transformer containing a storage capacitor for supporting the amplification voltage being made available at an output of the voltage-regulated direct voltage transformer; providing a voltage at the solenoid being higher than the amplification voltage at the predefined point in time by performing a step of charging the storage capacitor of the voltage-regulated direct voltage transformer to a pilot control voltage by means of the amplification voltage before the predefined point in time; and adapting a point in time of a start of the charging of the storage capacitor in dependence on an ageing of the fuel injector.

2. The method according to claim 1, wherein the charging of the storage capacitor begins at a point in time determined by calculation, with a result that the storage capacitor has the pilot control voltage precisely at the predefined point in time.

3. The method according to claim 1, wherein the charging of the storage capacitor begins at a point in time determined by calculation, with a result that the storage capacitor has the pilot control voltage before the predefined point in time.

4. The method according to claim 1, which further comprises carrying out the charging of the storage capacitor by means of the voltage- regulated direct voltage transformer.

5. The method according to claim 1, wherein the pilot control voltage is obtained from the amplification voltage and a tolerance supplement for the amplification voltage.

6. The method according to claim 1, wherein a point in time of a start of the charging of the storage capacitor is adapted in dependence on a temperature, determined by measurement, in surroundings of the fuel injector.

7. The method according to claim 6, which further comprises shortening a duration of the charging of the storage capacitor as the temperature drops.

8. The method according to claim 1, which further comprises shortening a duration of the charging of the storage capacitor as the ageing increases.

9. A computer program product for actuating a fuel injector for an internal combustion engine of a motor vehicle, the computer program product being loaded directly into a non-transitory internal memory of a digital computer and containing software code sections for performing a method for actuating the fuel injector having a coil drive with a solenoid and a magnet armature, wherein the magnet armature can be moved along a longitudinal axis by a magnetic field being generated by the solenoid, which method comprises the steps of: applying an amplification voltage to the solenoid at a predefined point in time to move the magnet armature from a closed position into an open position, wherein the amplification voltage being made available by a voltage-regulated direct voltage transformer from a supply voltage which is lower in comparison than the amplification voltage, the voltage-regulated direct voltage transformer containing a storage capacitor for supporting the amplification voltage being made available at an output of the voltage-regulated direct voltage transformer; providing a voltage at the solenoid being higher than the amplification voltage at the predefined point in time by performing a step of charging the storage capacitor of the voltage-regulated direct voltage transformer to a pilot control voltage by means of the amplification voltage before the predefined point in time; and adapting a point in time of a start of the charging of the storage capacitor in dependence on an ageing of the fuel injector.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

(1) FIG. 1 is a schematic illustration of a device for actuating a fuel injector for an internal combustion engine of a motor vehicle according to the prior art;

(2) FIG. 2 is a graph showing a current profile and a voltage profile during a conventional actuation of the fuel injector from FIG. 1;

(3) FIG. 3 is a schematic illustration of a device according to the invention for actuating the fuel injector for the internal combustion engine of the motor vehicle; and

(4) FIG. 4 is a graph of a current profile and a voltage profile during an inventive actuation of the fuel injector from FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION

(5) In the figures, identical elements are provided with identical reference symbols. Referring now to the figures of the drawings in detail and first, particularly to FIG. 1 thereof, there is shown a conventional control unit 10 for actuating a fuel injector 30 for an internal combustion engine of a motor vehicle. The fuel injector 30 which is not illustrated here in more detail is a conventional fuel injector which has, in a known fashion, a coil drive with a solenoid. Suitable excitation of the solenoid causes a magnetic field to be generated which moves a magnet armature of a coil drive along a longitudinal axis (displacement axis of the magnet armature). Connected to the magnet armature is a needle of the fuel injector which, as a function of its position, closes an opening of the fuel injector or clears it for a certain time for the purpose of fuel injection.

(6) In what is referred to as an amplification phase, an amplification voltage is applied to the coil drive of the fuel injector in order to move the magnet armature as quickly as possible from its closed position into its open position. Then, a holding voltage which is relatively low compared to the amplification voltage can be applied to the solenoid of the coil drive of the fuel injector in a holding phase, in order to hold the magnet armature in its open position. The holding voltage is generally applied in the form of a multiplicity of holding pulses, with the result that a predefined holding current is set. This differentiation is not taken into account for the present invention.

(7) The amplification voltage UDCDC, which constitutes a setpoint voltage, is made available by a control unit 10 at output terminals 22, 24. The control unit 10 contains for this purpose a direct voltage transformer 12, a storage capacitor 14, a voltage regulator 16, a computer unit (microcontroller) 18 and a switching element 20. The direct voltage transformer 12 generates an output voltage U2 from an input voltage U1. The input voltage U1, for example 12 V, is made available by a non-illustrated energy store of the motor vehicle. The output voltage U2 corresponds to the voltage UDCDC of the direct voltage transformer 12 at its output terminals and the output terminals 22, 24 of the control unit 10. The voltage UDCDC represents essentially the abovementioned amplification voltage whose level depends on a specification of the fuel injector 30. The amplification voltage is 65 V (=setpoint voltage) in this exemplary embodiment, as is illustrated also in the diagram in FIG. 2.

(8) The direct voltage transformer 12 is connected on the output side to the two terminals of the storage capacitor 14 and the fuel injector 30. For a person skilled in the art it is clear that the terminals of the direct voltage transformer 12 are connected here to the coil drive, i.e. the solenoid. The switching element 20 is connected between the already mentioned output terminal 22 and one of the output terminals of the direct voltage transformer 12. If a voltage is to be applied to the fuel injector 30 for the purpose of opening, the switching element 20 is closed. Otherwise, it is opened. The control of the switching position of the switching element 20 is carried out by the computer unit 18.

(9) The object of the storage capacitor 14 is to support the amplifier voltage UDCDC made available at the output of the direct voltage transformer 12, when the fuel injector 30 briefly draws a high current during the injection process for the purpose of opening. The energy which is necessary to open the fuel injector 30 is extracted from the storage capacitor 14, as a result of which the voltage between the output terminals 22, 24 and therefore at node 26 drops. This is clearly apparent in FIG. 2.

(10) FIG. 2 illustrates the profile of the amplification voltage UDCDC and the profile of a current I.sub.inj flowing into the fuel injector 30 or the solenoid thereof, together with information DCDC as to the points in time at which the voltage regulator 16 of the direct voltage transformer 12 is active. At the point in time t0, the opening process of the fuel injector 30 starts, i.e. the solenoid is energized. At the point in time t0, the specified amplification voltage UDCDC at a level of 65 V is present at the output 22, 24 of the control unit 10 and therefore at the fuel injector 30. Owing to the brief and high current extraction by the fuel injector 30 subsequent to the point in time t0, the amplification voltage UDCDC drops up to a point in time t1 by, for example, 6 V to 59 V. The level of this voltage drop of the amplification voltage UDCDC is dependent on the size of the storage capacity of the storage capacitor 14 and the internal resistance (ESR) thereof.

(11) The voltage drop at the output of the direct voltage transformer 12 is detected by the voltage regulator 16, which is connected on the input side to the node 26 between the output of the direct voltage transformer 12 and the storage capacitor 14. An output of the voltage regulator 16 is connected to the direct voltage transformer 12, as a result of which the latter brings about recharging of the storage capacitor 14 in order to regulate the amplification voltage UDCDC again to 65 V. At the point in time t2, the voltage UDCDC at the output of the direct voltage transformer 12 has reached the setpoint value of 65 V again.

(12) As is readily apparent from FIG. 2, the current I.sub.inj rises briefly after the point in time t0, remains between t0 and t2 at a level which permits the opening of the fuel injector 30, and drops again approximately at the point in time t1 to zero, as a result of which the fuel injector 30 begins to close again. It is also apparent that the direct voltage transformer (see the information DCDC) is active between t0 and t2.

(13) FIG. 3 shows the control unit 10 according to the invention for actuating a fuel injector 30 for an internal combustion engine of a motor vehicle. The design of the control unit 10 according to the invention differs from the design described in FIG. 1 only in that the voltage regulator 16 has two inputs 16a and 16b. The first input 16a is, as in FIG. 1, connected to the node 26 between the output of the direct voltage transformer 12 and the storage capacitor 14. At the first input 16a, the voltage at the output of the direct voltage transformer 12 or of the control unit 10 is detected in order to bring about recharging of the storage capacitor 14 in the case of a dropping voltage UDCDC, in order to regulate the amplification voltage UDCDC again to the setpoint value, i.e. in this example 65 V.

(14) In addition, the second input 16b is connected to the computer unit 18 which permits the behavior of the direct voltage transformer 12 to be influenced in the sense of pilot control.

(15) In order to reduce the voltage drop which is 6 V between t0 and t1 with the conventional configuration, before the point in time t0, i.e. at the point in time tx, the storage capacitor 14 is charged by the direct voltage transformer 12 by the rated amplification voltage of 65 V, with the result that the storage capacitor 14 has a voltage of, for example, 68 V at the point in time t0 (see FIG. 4). This voltage is referred to as a pilot control voltage.

(16) At the point in time t0, the opening process of the fuel injector 30 starts, i.e. the solenoid is energized and I.sub.inj rises at the point in time t0 and stays, by analogy with FIG. 2, at a high level until the closing of the fuel injector occurs. At the point in time t0, the pilot control voltage is at a level of 68 V at the output 22, 24 of the control unit 10 and therefore at the fuel injector 30 owing to the previously executed charging process. Owing to the brief and high current extraction by the fuel injector 30 subsequent to the point in time t0, the voltage drops again up to the point in time t1 by, for example, 6 V to 62 V. Compared to the specified amplification voltage of 65 V, the voltage drop is therefore only 3 V.

(17) The voltage drop at the output of the direct voltage transformer 12 is detected at the point in time t1 by the voltage regulator 16, since the latter is connected by its input 16a to the node 26 between the output of the direct voltage transformer 12 and the storage capacitor 14. A signal is generated at the output of the voltage regulator 16, as a result of which signal the voltage regulator 16 brings about recharging of the storage capacitor 14 in order to regulate the amplification voltage UDCDC again to 65 V. At the point in time t2, the voltage UDCDC at the output of the direct voltage transformer 12 has reached the setpoint value of 65 V again. Since only the voltage difference of 3 V now has to be compensated, the point in time t2 is reached before the point in time t2, which describes the conventional end of recharging. The profile of the conventional actuation is additionally illustrated in FIG. 4 for the purpose of comparison.

(18) The period of time between the point in time tx at which the charging of the storage capacitor 14 begins and the point in time t0 at which the fuel injector 30 opens, can be determined by a calculation. The period of time is dependent on the configuration of the control unit 10 and the actual behavior of the fuel injector 30. Once the period of time has been determined, it can be used constantly by the computer unit 18 for every opening process of the fuel injector 30.

(19) In one refinement it is possible for the period of time to be adapted as a function of the temperature in the surroundings of the fuel injector 30. Here, the duration of the charging of the storage capacitor 14 can be shortened or lengthened as a function of the temperature. In particular, there is provision for the duration of the charging of the storage capacitor to be shortened as the temperature drops. This means that the start of charging occurs relatively late compared to an actuation during which the temperature is not taken into account.

(20) In a further refinement, the point in time of the start of charging of the storage capacitor 14 can be adapted as a function of ageing of the fuel injector 30. Therefore the duration of the charging of the storage capacitor 14 is shortened or lengthened as a function of a state of ageing which is determined, for example, by computer and stored in the computer unit 18 or determined by measurement. In particular there is provision for the duration of the charging of the storage capacitor 14 to be shortened as the ageing increases. Therefore the start of charging occurs relatively late compared to an actuation during which the ageing is not taken into account.

(21) If the pilot control voltage which is aimed at in the scope of the pilot control is reached before the point in time t0, the voltage of the storage capacitor 14 is thus kept constant at the level of the pilot control voltage up to the point in time t0.

(22) The proposed method is based on knowledge-based, premature switching on of the direct voltage transformer 12 in order to synchronize the start of the charging or of recharging of the storage capacitor 14 with the start of the injection. An advantage of this procedure is that the storage capacitor 14 can be made relatively small compared to a conventional actuation, since the storage capacitor 14 experiences only a relatively small voltage drop in comparison. Alternatively, it is possible to use components in the control unit which entail lower fabrication costs.