PRECISE DETERMINATION OF THE ELECTRICAL RESISTANCE OF A FUEL INJECTOR HAVING A SOLENOID DRIVE

Abstract

The invention relates to a method for determining an electrical resistance value for a fuel injector having a solenoid drive. The method comprises the following: (a) applying a voltage pulse to the solenoid drive of the fuel injector, (b) sensing a temporal progression of the current intensity of a current (I) flowing through the solenoid drive, (c) calculating a series of linked fluxes () as a function of current intensity (I), wherein each linked flux () is calculated on the basis of the temporal progression of voltage and current intensity (I) and on the basis of a hypothetical resistance value from a series of hypothetical resistance values, and (d) selecting one of the hypothetical resistance values as a determined resistance value on the basis of an analysis of the calculated series of linked fluxes (). The invention further relates to a method for determining a temperature of a coil of a fuel injector having a solenoid drive, to a motor controller, and to a computer program.

Claims

1. A method for determining an electrical resistance value for a fuel injector having a solenoid drive, said method comprising: applying a voltage pulse to the solenoid drive of the fuel injector, ascertaining a temporal progression of current strength of a current that is flowing through the solenoid drive, calculating a series of linked fluxes as a function of the current strength, wherein each linked flux is calculated based on the temporal progression of the voltage and the current strength and on a hypothetical resistance value from a series of hypothetical resistance values, and selecting one of the hypothetical resistance values as a determined resistance value based on an analysis of the calculated series of linked fluxes.

2. The method as claimed in claim 1, wherein the analysis of the calculated series of linked fluxes comprises analyzing a curve behavior for each linked flux as a function of the current strength.

3. The method as claimed in claim 2, wherein the curve behavior is analyzed in the region of a maximum current strength.

4. The method as claimed in claim 3, wherein the determined resistance value selected is the hypothetical resistance value for which the curve behavior of the corresponding flux of the corresponding flow demonstrates the smallest change in the region of the maximum current strength.

5. The method as claimed in claim 2, wherein the analysis of the curve behavior comprises calculating and evaluating at least one of a first and second derivative of each flux as a function of the current strength.

6. The method as claimed in claim 1, wherein a voltage pulse is applied to the solenoid drive of the fuel injector by switching on and off a vehicle battery voltage.

7. The method as claimed in claim 1, wherein the series of hypothetical resistance values have a predetermined step size between individual hypothetical resistance values.

8. A method for determining a temperature of a coil of a fuel injector comprising a solenoid drive, said method comprising: determining a first resistance value for the coil based on a known reference temperature, determining a second resistance value for the coil according to the method as claimed in claim 1, and calculating the temperature based on the determined second resistance value, the determined first resistance value and the known reference temperature.

9. An engine control unit for a vehicle, said engine control unit configured to perform the method as claimed in claim 1.

10. An apparatus for determining an electrical resistance value for a fuel injector having a solenoid drive, the apparatus comprising: a processor; and a non-transitory memory device coupled to the processor, the non-transitory memory device storing a computer program which, when by the processor, causes the apparatus to perform the method as claimed in claim 1.

Description

[0041] Further advantages and features of the present invention are disclosed in the following exemplary description of a preferred embodiment.

[0042] FIG. 1 illustrates the temporal progressions of the voltage and the current strength when determining an electrical resistance value in accordance with an exemplary embodiment.

[0043] FIG. 2 illustrates a series of calculated relationships between linked flux and current strength in accordance with an exemplary embodiment.

[0044] FIG. 3 illustrates an enlarged section from FIG. 2.

[0045] Reference is made to the fact that the embodiment described hereinunder is merely a limited selection of possible embodiment variants of the invention.

[0046] FIG. 1 illustrates the temporal progression of the voltage 101 and the temporal progression of the current strength 102 when the method is being performed in accordance with the invention for determining an electrical resistance value for a fuel injector having a solenoid drive. At the point in time t=5 ms, a voltage of approximately 12V (battery voltage in the vehicle) is applied to the fuel injector whose electrical resistance value is to be measured. The voltage is switched off at the point in time t=0 ms so that a voltage pulse is applied to the solenoid drive of the fuel injector for a duration of 5 ms. While the voltage 101 is being applied, a current flows through the solenoid drive whose current strength 102 initially increases relatively quickly (until about a point in time t=3 ms) and subsequently approaches an asymptotic value of approximately 7.3 A relatively slowly. At the end of the voltage pulse, the current strength 102 drops back rapidly to 0 A.

[0047] In order to determine the electrical resistance value for the fuel injector, the temporal progressions 101 and 102 are ascertained and stored in digital format.

[0048] A series of calculations is subsequently performed, wherein each calculation corresponds to a hypothetical resistance value from a series of hypothetical resistance values. To be more specific, the linked magnetic flux .sub.k is calculated for each hypothetical resistance R.sub.coil,k and based on the ascertained temporal progressions of the voltage 101 and current strength 102:

.sub.k(I,t)=.sub.0.sup.t(U(t)R.sub.coil,k.Math.I(t))dt,k=0,1,2, . . . ,N1.

[0049] Each calculated linked flux .sub.k is stored together with the current strength I as a characteristic curve diagram or function.

[0050] FIG. 2 illustrates a series of such calculated relationships between linked flux .sub.k and current strength I. To be more specific, FIG. 2 shows 30 (thirty) calculated /I relationships, wherein each relationship corresponds to a hypothetical value R.sub.coil,k. At the beginning of the voltage pulse (cf. FIG. 1), in other words at the beginning of the increase in current, all the 30 relationships progress essentially in an identical manner. This is demonstrated by the reference numeral 211. If the current strength I achieves a value between approximate 3 A and 4 A, the curves separate, wherein the upper curves 212 have a curve that increases upwards as the current strength increases and the lower curves 213 drop slightly as the current strength increases. These two behaviors are physically not possible (as explained in the introduction). Instead, it can be identified that the relationship(s) 214 in the middle of the bundle comprise in contrast a progression that is expedient in the physical sense, in other words has an almost flat asymptotic progression.

[0051] FIG. 3 illustrates an enlarged section 320 from FIG. 2 in the region of the maximum current strength, in particular for I between approximately 5.9 A and 7.3 A. It is clearly evident in section 320 that the curve 312 curves upwards in an ever increasing manner, which is physically not commensurate with a saturation. The curve 313 comprises on the other hand a slightly falling value of the linked flux shortly prior to achieving the maximum current strength, which also corresponds in the physical sense to saturation not being present. Consequently, it can be concluded that the hypothetical resistance values that correspond to the curves 312 and 313 deviate from the actual resistance value. The curve 314 comprises as the only one below the 30 curves prior to achieving the maximum current strength a flat asymptotic progression. Even the upper adjacent curve 315 comprises a curve that is slightly increasing upwards, in other words the identical tendency as the curve 312. The lower adjacent curve 316 comprises on the other hand a slightly falling progression, in other words the identical tendency as the curve 313.

[0052] In other words, the hypothetical resistance value that has resulted in the curve 314 is to be selected as the determined resistance value.

[0053] As far as the technical aspect of this calculation is concerned, this selection can be performed for example by analyzing the first and/or the second derivative for each individual curve. The correct curve is the curve for which the first derivative (in the proximity of the maximum current strength) remains as constant as possible, or to express it differently, the curve for which the value of the second derivative (in the proximity of the maximum current strength) is the closest to zero.

LIST OF REFERENCE NUMERALS

[0054] 101 Temporal progression of the voltage [0055] 102 Temporal progression of the current strength [0056] 211 Curves [0057] 212 Curves [0058] 213 Curves [0059] 214 Curves [0060] 312 Curve [0061] 313 Curve [0062] 314 Curve [0063] 315 Curve [0064] 316 Curve [0065] 320 Section