Determination of a point in time of a predetermined state of a fuel injector

Abstract

A method for determining a first time at which a fuel injector having a solenoid drive is in a first predetermined opening state. The method includes the following: (a) determining a second time at which the fuel injector is in a second predetermined state, (b) determining a stroke value of a moving component of the fuel injector, which stroke value corresponds to a movement path of the moving component which is covered when the fuel injector transitions between the first predetermined opening state and the second predetermined opening state, and (c) determining the first time at which the fuel injector is in the first predetermined opening state, on the basis of the second time and the stroke value. A method for actuating a fuel injector having a solenoid drive, an engine controller and a computer program.

Claims

1. A method for determining a first time at which a fuel injector having a solenoid drive is in a first predetermined opening state, the method comprising: providing a fuel injector; and providing at least one moving component being part of the fuel injector; determining a second time at which the fuel injector is in a second predetermined opening state; moving the at least one moving component on a movement path from the first predetermined opening state to the second predetermined opening state; determining a stroke value of the at least one moving component of the fuel injector, which the stroke value corresponds to the movement path of the at least one moving component which is covered when the fuel injector transitions between the first predetermined opening state and the second predetermined opening state; determining a first time at which the fuel injector is in the first predetermined opening state, on the basis of the second time and the stroke value, wherein determining the stroke value further comprising: providing a data set which represents a relationship between the interlinked magnetic flux and the current intensity in the solenoid drive in the event of actuation of the fuel injectors; detecting the data set; and analysing the data set in order to determine the stroke value.

2. The method of claim 1, further comprising the steps of: analysing the data set by forming a characteristic curve of the stroke value on the basis of the data set, and detecting shifts in the profile of the characteristic curve.

3. The method of claim 1, determining the first time further comprising the steps of: providing a reference stroke value; providing a corrected second time; determining a difference between the stroke value and the reference stroke value; determining the corrected second time on the basis of the second time, the difference and a correction factor, and determining the first time on the basis of the corrected second time and a predetermined relationship between the first opening state and the second opening state.

4. The method of claim 1, further comprising the steps of: providing an opening phase such that the first predetermined opening state of the fuel injector is the start of the opening phase, and the second predetermined opening state is the end of the opening phase.

5. The method of claim 4, further comprising the steps of: providing the at least one moving component to be a needle, and the stroke value is a needle stroke value.

6. A method for actuating a fuel injector having a solenoid drive, comprising the steps of: providing a fuel injector; providing a solenoid drive being part of the fuel injector; providing a reference time; providing a boost voltage for opening the fuel injector; determining a first time at which the fuel injector is in a first predetermined opening state, wherein the first predetermined state is an idle stroke location of the fuel injector comprising the steps of: providing at least one moving component being part of the fuel injector; determining a second time at which the fuel injector is in a second predetermined opening state; determining a stroke value of the at least one moving component of the fuel injector, which the stroke value corresponds to a movement path of the at least one moving component which is covered when the fuel injector transitions between the first predetermined opening state and the second predetermined opening state; determining a first time at which the fuel injector is in the first predetermined opening state, on the basis of the second time and the stroke value; actuating the fuel injector on the basis of the determined first time; reducing a duration between the application of the boost voltage for opening the fuel injector and the application of a voltage for closing the fuel injector if it is determined that the first time occurs later than the reference time, or increasing duration between the application of the boost voltage for opening the fuel injector and the application of the voltage for closing the fuel injector if it is determined that the first time occurs earlier than the reference time.

7. The method of claim 6, determining the stroke value further comprising the steps of: providing a data set which represents a relationship between the interlinked magnetic flux and the current intensity in the solenoid drive in the event of actuation of the fuel injectors; detecting the data set; analysing the data set in order to determine the stroke value.

8. The method of claim 7, further comprising the steps of: analysing the data set by forming a characteristic curve of the stroke value on the basis of the data set, and detecting shifts in the profile of the characteristic curve.

9. The method of claim 6, determining the first time further comprising the steps of: providing a reference stroke value; providing a corrected second time; determining a difference between the stroke value and the reference stroke value; determining the corrected second time on the basis of the second time, the difference and a correction factor, and determining the first time on the basis of the corrected second time and a predetermined relationship between the first opening state and the second opening state.

10. The method of claim 6, further comprising the steps of: providing an opening phase such that the first predetermined opening state of the fuel injector is the start of the opening phase, and the second predetermined opening state is the end of the opening phase.

11. The method of claim 10, further comprising the steps of: providing the at least one moving component to be a needle, and the stroke value is a needle stroke value.

12. An engine controller for a vehicle, which engine controller is designed to determine a first time at which a fuel injector having a solenoid drive is in a first predetermined opening state, comprising: a fuel injector; at least one moving component being part of the fuel injector, wherein the at least one moving component is moved from the first predetermined opening state to a second predetermined opening state along a movement path, wherein the first predetermined state is an idle stroke location of the at least one moving component and wherein a stroke value of the at least one moving component is determined with the engine controller wherein a second time at which the fuel injector is in a second predetermined opening state is determined, and the first time at which the fuel injector is in the first predetermined opening state is determined with the engine controller on the basis of the second time and the stroke value.

13. The engine controller for a vehicle of claim 12, further comprising: a data set, the data set being analysed and detected to determine the stroke value; wherein the data set represents a relationship between the interlinked magnetic flux and the current intensity in the solenoid drive in the event of actuation of the fuel injectors.

14. The engine controller for a vehicle of claim 13, wherein the data set is analysed by forming a characteristic curve of the stroke value on the basis of the data set, and detecting shifts in the profile of the characteristic curve.

15. The engine controller for a vehicle of claim 12, determining the first time further comprising the steps of: providing a reference stroke value; providing a corrected second time; determining a difference between the stroke value and the reference stroke value; determining the corrected second time on the basis of the second time, the difference and a correction factor; and determining the first time on the basis of the corrected second time and a predetermined relationship between the first opening state and the second opening state.

16. The engine controller for a vehicle claim 12, further comprising an opening phase, wherein the first predetermined opening state of the fuel injector is the start of the opening phase, and the second predetermined opening state is the end of the opening phase.

17. The engine controller for a vehicle claim 16, the at least one moving component further comprising a needle, and the stroke value is a needle stroke value.

18. The method of claim 2, wherein the stroke value is the time for the at least one moving component to move from the first predetermine opening state to the second predetermined opening state based upon the data set.

19. The method of claim 7, wherein the stroke value is the time for the at least one moving component to move from the first predetermine opening state to the second predetermined opening state based upon the data set.

20. The engine controller of claim 13, wherein the stroke value is the time for the at least one moving component to move from the first predetermine opening state to the second predetermined opening state based upon the data set.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further advantages and features of the present invention may be gathered from the following exemplary description of a preferred embodiment.

(2) FIG. 1 shows a fuel injector with a solenoid drive.

(3) FIG. 2 shows an armature position, needle position and rate of injection as functions of time for two fuel injectors with a different needle stroke.

(4) FIG. 3 shows a -I characteristic curve (PSI-I characteristic curve) for determining, according to the invention, a stroke value for a fuel injector.

(5) FIG. 4 shows a flowchart of a method according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

(6) The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.

(7) It should be noted that the embodiments described below are merely a limited selection of possible variant embodiments of the invention.

(8) FIG. 1 shows a sectional view of a fuel injector 100 with a solenoid drive (solenoid injector). The injector 100 includes, in particular, a solenoid drive with a coil 102 and an armature 104. When a voltage pulse is applied to the coil 102, the magnetic armature 104 moves in the direction of the wide part of the nozzle needle 106 and then, after overcoming the idle stroke 114 (against the force of the spring 110), presses the nozzle needle upward against the spring forces exerted by the springs 110 and 132 until the armature 104 stops against the pole shoe 112. When the voltage pulse is ended, the armature 104 and the nozzle needle 106 move back down again to the starting position on the hydro disk 108.

(9) The solenoid injector 100 shown in FIG. 1 has several features which are known per se and are only of negligible significance for the present invention; therefore, these are not described in detail. These features include, in particular, valve body 116, integrated seat guide 118, ball 120, seal 122, housing 124, plastic 126, disk 128, metal filter 130 and calibration spring 132.

(10) FIG. 2 shows armature position 212, 214, needle position 222, 224 and rate of injection (ROI) 232, 234 as functions of time for two fuel injectors with a different needle stroke. Apart from the needle strokes, the two fuel injectors are identical and are electrically actuated in an identical manner.

(11) Specifically, the upper image 210 shows the armature position 212 (curve with a solid line) for a fuel injector with a 60 m needle stroke and the armature position 214 (curve with a dashed line) for a fuel injector with an 80 m needle stroke. The middle image 220 shows the needle position 222 (curve with a solid line) for the fuel injector with a 60 m needle stroke and the needle position 224 (curve with a dashed line) for the fuel injector with an 80 m needle stroke. The lower image 230 shows the rate of injection (ROI) 232 (curve with a solid line) for the fuel injector with a 60 m needle stroke and the rate of injection 234 (curve with a dashed line) for the fuel injector with an 80 m needle stroke.

(12) Images 210, 220 and 230 show that the difference in the needle stroke of 20 m leads to a difference of 38 s between the times at which the opening state OPP2 (end of the needle movement) is reached, that is to say OPP=38 s. Secondly, the difference between the times at which the opening state OPP1 (beginning of the needle movement) is reached is only 4 s, that is to say OPP1=4 s. This is attributed to the fact that the magnetic force is initially slightly different owing to the magnetic starting air gap. If the OPP1 time is then estimated simply on the basis of detection of the OPP2 time, as was frequently done up until now, this may lead to a deviation of 34 s, that is to say more than eight times too much.

(13) Furthermore, it is clearly shown in image 230 that the total injection quantity is considerably greater when the needle stroke is 80 s. Although the actuation is the same, the injection operation ends considerably later specifically in this case, cf. curve 234.

(14) These deviations may be compensated for by the method according to the invention by the actual needle stroke being regularly determined and being taken into account when a (first) time is determined on the basis of another (second) time. The method according to the invention will be described in more detail below in conjunction with FIG. 4.

(15) FIG. 3 shows a characteristic curve (PSI-I characteristic curve) 300 for determining, according to the invention, a stroke value for a fuel injector, such as the fuel injector 100 shown in FIG. 1 for example. The characteristic curve 300 is substantially made up of two curve elements, wherein the lower curve element is made up of curve sections 310, 312, 314, 316 and 318 and corresponds to opening of the fuel injector 100. The upper curve element is made up of curve sections 320, 322 and 324 and corresponds to closing of the fuel injector 100. Two shifts of the curved profile take place along the lower curve element.

(16) The first shift is created on account of the idle stroke, i.e. by the armature being moved from its inoperative position until it makes contact with the needle and then being braked or stopped. In other words, the magnetic force is firstly built up along the curve section 310, then the armature moves along the curve section 312 as far as the needle (idle stroke), where it remains stationary along the curve section 314 while a further magnetic force is built up. The second shift is created on account of the needle stroke, i.e. by both the armature and also the needle together moving until they come to a standstill when the armature stops on the pole piece. The movement of the armature and the needle runs along the curve section 316 and a further build-up of the magnetic force takes place along the curve section 318.

(17) The idle stroke and the needle stroke is determined, as described further below, by determining the shifts, for example by detecting the distance between tangents 311 (that is to say extrapolation of the curve section 310) and the curve sections 314 or between tangents 315 (that is to say extrapolation of the curve section 314) and the curve section 318.

(18) The closing process proceeds in a similar manner, but in reverse: The magnetic force is firstly reduced along the curve section 320. The needle and the armature then together move away from the pole piece and then the armature moves away from the needle as far as its inoperative position on the hydro disk. These two movements run along the curve section 322. Finally, the magnetic force is further reduced along the curve section 324.

(19) In order to record the characteristic curve 300, the injector 100 is driven with a low voltage, e.g. 10 V, so that the idle stroke movement and the needle movement are separated into two distinct movements. Low magnetic forces are created due to the low drive voltage. The idle stroke movement takes place (along the curve section 312) after the force of the spring 110 has been overcome. The armature 104 moves toward the needle 106 and remains inoperative together with the needle 106 since the force of the calibration spring 132 counteracts a movement. Owing to a further increase in the magnetic force, the force of the calibration spring 132 is overcome and the armature 104 and the needle 106 move (along the curve section 316) until the armature 104 comes to rest against the pole shoes 112.

(20) The stroke value is given by the differences in the curve section before the movement and in the curve section after the movement. In other words, the idle stroke may be determined by determining a flow difference (given a suitable current intensity) between the tangent 311 (that is to say the extrapolated continuation of the curve section 310) and the curve section 314. In the same way, the needle stroke is determined by determining a flow difference between the tangent 315 (that is to say the extrapolated continuation of the curve section 314) and the curve section 318. A possible evaluation would be, for example, ascertaining the difference in the PSI value at 2 A (0.0004 Wb) and then multiplication by a factor. In this example, the factor 125000 m/Wb would then result in an idle stroke of 50 m (0.0004 Wb*125000 m/Wb=50 m).

(21) The characteristic curve 300 is determined by measuring the current which flows through the coil 102 and the voltage which is applied to the coil 102, and also by calculating the interlinked magnetic flux LP from the current, the voltage and the electrical resistance of the coil 102. The measured voltage u(t) is made up of a resistive component (i(t)*R) and an inductive component (u.sub.ind(t)). Here, the inductive voltage is calculated from the time derivative of the interlinked magnetic flux, wherein depends on the change in current i(t) and the air gap x(t).

(22) $u\left(t\right)=i\left(t\right)R+u_{\mathrm{ind}}\left(t\right)=i\left(t\right)R+\frac{d\left(i,x\right)}{\mathrm{dt}}=i\left(t\right)R+\left(\frac{d\left(i,x\right)}{\mathrm{di}}\frac{\mathrm{di}}{\mathrm{dt}}+\frac{d\left(i,x\right)}{\mathrm{dx}}\frac{\mathrm{dx}}{\mathrm{dt}}\right)$

(23) On slow actuation, the magnetic component of the induction due to a change in current is small.

(24) $u_{\mathrm{ind}1}=\frac{d\left(i,x\right)}{\mathrm{di}}\frac{\mathrm{di}}{\mathrm{dt}}$

(25) The mechanical part of the induction due to the armature movement then describes the strokes (idle stroke and/or working stroke) of the fuel injector.

(26) $u_{\mathrm{ind}2}=\frac{d\left(i,x\right)}{\mathrm{dx}}\frac{\mathrm{dx}}{\mathrm{dt}}$

(27) By transposition and integration, the interlinked magnetic flux may be calculated as follows:
=(u(t)i(t)R)dt

(28) FIG. 4 shows a flowchart of a method according to the invention for determining a first time at which a fuel injector having a solenoid drive is in a first predetermined opening state. The first predetermined state may be, for example, OPP1.

(29) A second time at which the fuel injector is in a second predetermined state is determined in step 410. The second predetermined state may be, for example, OPP2.

(30) A stroke value of a moving component of the fuel injector, which stroke value corresponds to a movement path of the moving component which is covered when the fuel injector transitions between the first predetermined opening state and the second predetermined opening state, is determined in step 420. The stroke value may be, for example, the value of the needle stroke.

(31) The first time at which the fuel injector is in the first predetermined opening state is then determined in step 430 on the basis of the second time and the stroke value.

(32) The first time may preferably be such that a difference between the stroke value determined in step 420 and a reference stroke value (for example a stroke value which is prespecified by the manufacturer) is determined. In other words, the current deviation in the stroke value is determined. The determined second time is then corrected depending on the determined difference. This may be done, for example, using a correction factor
T2k=T2k*D

(33) Here, T2 is the second time, T2k is the corrected second time, k is the correction factor, and D is the difference.

(34) With reference to the values shown in FIG. 2, this gives T2k=38 s1.7 s/m*20 m=4 s. The correction factor is k=34 s/20 m=1.7 s/m here.

(35) After correction of the second time, the first time may then be determined using the known relationship between the two times, that is to say in the same way as if the needle stroke were equal to the reference value.

(36) Overall, the present invention establishes a method which is simple and easy to implement and by way of which accurate injection quantities may be achieved depending on changes in the stroke value, for example owing to wear.

(37) The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.

LIST OF REFERENCE SYMBOLS

(38) 100 Fuel injector 102 Coil 104 Armature 106 Needle 108 Hydro disk 110 Spring 112 Pole shoe 114 Idle stroke 116 Valve body 118 Integrated seat guide 120 Ball 122 Seal 124 Housing 126 Plastic 128 Disk 130 Metal filter 132 Calibration spring 210 Image 212 Armature position as a function of time 214 Armature position as a function of time 220 Image 222 Needle position as a function of time 224 Needle position as a function of time 230 Image 232 Rate of injection as a function of time 234 Rate of injection as a function of time 300 -I characteristic curve 310 Curve section 311 Tangent 312 Curve section 314 Curve section 315 Tangent 316 Curve section 318 Curve section 320 Curve section 322 Curve section 324 Curve section 410 Method step 420 Method step 430 Method step