METHOD FOR DETERMINING A REFERENCE CURRENT VALUE FOR ACTUATING A FUEL INJECTOR

Abstract

A method for determining a reference current value for actuating a fuel injector, comprising a solenoid drive, for an internal combustion engine of a motor vehicle is described. The method comprises the following: (a) acquiring a multiplicity of current profiles with repeated actuation of the fuel injector, wherein each current profile has a temporal progression of the current strength of a current flowing through the solenoid drive, and wherein each actuation of the fuel injector comprises the following steps: (aa) applying a boost voltage to the solenoid drive of the fuel injector until the current strength of the current flowing through the solenoid drive reaches a first predetermined value, (ab) waiting for the current strength to reach a second predetermined value during a first free-wheeling phase, (ac) applying the boost voltage to the solenoid drive again until the current strength reaches the first predetermined value, and (ad) waiting for the current strength to reach the second predetermined value during a second free-wheeling phase, wherein the first predetermined value is varied for each actuation, the method also comprising (b) determining a multiplicity of magnetic flux profiles, wherein each magnetic flux profile corresponds to one of the multiplicity of acquired current profiles, and (c) selecting the reference current value on the basis of an analysis of the associated current profiles and magnetic flux profiles.

Claims

1. A method for determining a reference current value for actuating a fuel injector comprising a solenoid drive, for an internal combustion engine of a motor vehicle, the method comprising acquiring a plurality of current profiles with repeated actuation of the fuel injector, wherein each current profile has a temporal progression of a current flowing through the solenoid drive, and wherein each actuation of the fuel injector comprises the following steps: applying a boost voltage to the solenoid drive of the fuel injector until a current flowing through the solenoid drive reaches a first predetermined value; waiting for the current through the solenoid drive to reach a second predetermined value during a first free-wheeling phase; applying a boost voltage to the solenoid drive until the current reaches the first predetermined value; and waiting for the current strength to reach the second predetermined value during a second free-wheeling phase; wherein the first predetermined value is varied for each actuation, the method also comprises: determining a multiplicity of magnetic flux profiles, wherein each magnetic flux profile corresponds to one of the multiplicity of acquired current profiles, and selecting the reference current value on the basis of an analysis of the associated current profiles and magnetic flux profiles.

2. The method of claim 1, wherein analysis of the associated current profiles and flux profiles comprises: comparing a first relationship between the current and the magnetic flux during a first free-wheeling phase with a second relationship between the current and the magnetic flux during a second free-wheeling phase.

3. The method of claim 2, wherein selection of the reference current value comprises selecting the lowest value of the first predetermined value at which the first relationship is essentially the same as the second relationship.

4. The method of claim 3, wherein the determination of a multiplicity of magnetic flux profiles is carried out by calculations on the basis of the current, voltage and electrical resistance of the solenoid drive.

5. The method of claim 4, further comprising determining an opening time of the fuel injector for one of the acquired current profiles on the basis of an analysis of the current profile and of the corresponding magnetic flux profile.

6. The method of claim 5, wherein the analysis of the current profile and of the corresponding flux profile comprises determining an associated pair of current strength and magnetic flux, in which a first relationship between the current strength and the magnetic flux during the first free-wheeling phase differs from a second relationship between the current strength and the magnetic flux during the second free-wheeling phase.

7. A method for actuating a fuel injector, comprising a solenoid drive, for an internal combustion engine of a motor vehicle, the method comprising determining a reference current value by carrying out the method as claimed in one of the preceding claims, and applying a boost voltage to the solenoid drive of the fuel injector until the current strength of the current flowing through the solenoid drive reaches the determined reference current value.

Description

[0037] FIG. 1 shows a graphic illustration of a multiplicity of current profiles which are used according to the invention to determine a reference current value.

[0038] FIG. 2 shows a graphic illustration of a multiplicity of sound signals which correspond to the current profiles shown in FIG. 1.

[0039] FIG. 3 shows a graphic illustration of a magnetic phase space corresponding to the current profiles shown in FIG. 1.

[0040] It is to be noted that the embodiments described below constitute merely a restricted selection of possible embodiment variants of the invention.

[0041] FIG. 1 shows a graphic illustration 101 of a multiplicity of current profiles 111 to 116 which are used according to the invention to determine a reference current value. The current profiles 111 to 116 are arranged in the illustration 101 in such a way that they all reach their first maximum value (or first predetermined value) at the time t=0.

[0042] Each current profile 111 to 116 is adopted according to the invention by the engine control unit in such a way that a boost voltage (i.e. a voltage of e.g. 40 V to 60 V which is increased compared to the on-board power system voltage) is first applied to the solenoid drive of a fuel injector. The current strength of the current flowing through the solenoid drive is measured, sampled and stored by the control unit. If the current strength reaches a first predetermined value (peak current of the profile), the boost voltage is switched off and the fuel injector passes into a first free-wheeling phase in which no further electrical energy is supplied. This leads to a situation in which the current strength decreases with time. If the current strength reaches a second predetermined value, the first free-wheeling phase is ended and the boost voltage is applied to the solenoid drive again, with the result that the current strength rises again. If the current strength then reaches the first predetermined value again, the boost voltage is switched off again and a second free-wheeling phase follows until the current strength reaches the second predetermined value again. This is followed by a holding phase in which the fuel injector is held open until the start of the closing process, by applying a holding voltage thereto, until the desired injection quantity is reached.

[0043] Each individual current profile 111 to 116 is, in other words, produced by applying a second boost phase. Therefore, each current profile also has two free-wheeling phases. By comparing these two free-wheeling phases, it is then possible, as described in more detail below, to derive valuable information relating to the opening time of the fuel injector. The current profiles 111 to 116 can advantageously be acquired during the normal operation of the fuel injector.

[0044] The six current profiles 111 to 116 shown in FIG. 1 differ, in particular, in that the predetermined value of the current strength at which the boost phases are ended, is selected differently for each current profile 111 to 116. This, of course, also influences the duration of the boost phases. For the current profile 111 the first predetermined value is approximately 10 A, for the current profile 112 the first predetermined value is approximately 12 A, for the current profile 113 the first predetermined value is approximately 14 A, for the current profile 114 the first predetermined value is approximately 16 A, for the current profile 115 the first predetermined value is approximately 128, and for the current profile 116 the first predetermined value is approximately 20 A.

[0045] FIG. 2 shows a graphic illustration 202 of a multiplicity of sound signals 221 to 226 from an acoustic sensor on the fuel injector, which sound signals correspond to the current profiles 111 to 116 shown in FIG. 1. To be more precise, the sound signal 221 corresponds to the current profile 111 shown in FIG. 1, the sound signal 222 corresponds to the current profile 112 shown in FIG. 1, the sound signal 223 corresponds to the current profile 113 shown in FIG. 1, the sound signal 224 corresponds to the current profile 114 shown in FIG. 1, the sound signal 225 corresponds to the current profile 115 shown in FIG. 1, and the sound signal 226 corresponds to the current profile 116 shown in FIG. 1.

[0046] The acoustic sensor is mounted in such a way that it can sense the acoustic sounds which are produced by movements in the fuel injector, for example when the armature impacts at the end of the opening process. From illustration 202 it is apparent that the end of the opening process occurs earlier for current profiles with a high first predetermined value and later for current profiles with a lower first predetermined value. In particular, the curves 226, 225 and 224 show that the end of the opening process for the corresponding current profiles 116, 115 and 114 occurs before the end of the first boost phase (t=0). Furthermore, the curves 222 and 221 show that the end of the opening process for the corresponding current profiles 112 and 111 occurs after the end of the first boost phase (t=0). However, for the curve 223 the end of the opening process coincides essentially with the end of the first boost phase (t=0), with the result that actuation of the fuel injector with a peak current value equal to the first predetermined value for the current profile 113 would give rise to a situation in which the end of the opening process occurs chronologically very close to the end of the corresponding boost phase.

[0047] The illustration in FIG. 2 is based on laboratory measurements in which an acoustic sensor has been specifically used. It serves merely for the purpose of illustration and is not as such part of the method according to the invention.

[0048] FIG. 3 shows a graphic illustration 303 of a magnetic phase space, that is to say a relationship between the magnetic flux and the current strength I, decoupled from time, corresponding to the current profiles 111 to 116 shown in FIG. 1. The magnetic flux is preferably calculated by the control unit on the basis of the respective current profile, voltage profile and coil resistance.

[0049] The relationship between the magnetic flux and the coil current is explained in more detail first with reference to the current profile 111 in FIG. 1. Before the start of the first boost phase, the magnetic flux is 0 mWb and the coil current is 0 A. The first rise in current of the current profile 111 (from t0.3 ms to t=0 ms) in FIG. 1 runs along the curve section 330 in FIG. 3. In the case of a current strength of just above 10 A the boost voltage is switched off and both the current strength and the magnetic flux now drop along the curve sections 331a and 337 up to the point 338, which corresponds to the end of the first free-wheeling phase. The subsequent rise in current in the second boost phase then runs along the curve section 339 until the current strength of just above 10 A is reached again at the end of the second boost phase. The subsequent second free-wheeling phase then runs along the curve sections 331b (at which the magnetic flux is somewhat larger than at the curve section 331a) and 337 and ends again at the point 338. Finally, the closing of the fuel injector runs along the curve section 340.

[0050] As can be inferred from FIG. 3, it is the case for the current profile 111 in FIG. 1 that the relationship (first relationship) between the current and the magnetic flux during the first free-wheeling phase (curve section 331a) is not the same as the relationship (second relationship) between the current and the magnetic flux during the second free-wheeling phase (curve section 331b). This can be attributed to the fact that, as has also been explained above in conjunction with FIG. 2, the opening process is not yet completed before the start of the first free-wheeling phase. In other words, movement is still occurring in the fuel injector during the course of the first free-wheeling phase.

[0051] A similar behavior can be observed in FIG. 3 for the current profiles 112 and 113 in FIG. 1, as has just been discussed with reference to the current profile 111. More specifically, a first relationship between the magnetic flux and the current can be seen along the curve sections 332a and 333a, and a second relationship between the magnetic flux and the current can be seen along the curve sections 332b and 333b.

[0052] No difference between the free-wheeling phases can be seen any more for the current profiles 114, 115 and 116 in FIG. 1. More specifically, the relationship between the magnetic flux and the current in both free-wheeling phases is essentially the same. For the current profile 114 both free-wheeling phases run along curve sections 334 and 337, for the current profile 115 both free-wheeling phases run along the curve sections 335 and 337, and for the current profile 116 both free-wheeling phases run along the curve sections 336 and 337.

[0053] According to the invention, the engine controller consequently selects the first predetermined value of the current profile 114, that is to say 16 A, as a peak current for the actuation of the fuel injector, in order to position the end of the boost phase as close as possible to the end of the opening process. The injection quantity can be controlled very precisely by this synchronization of the boost phase and the opening process.

[0054] Furthermore, the engine controller can determine the precise time at which the opening process ends for each individual current profile 111 to 113. More specifically, the engine controller determines the point in the magnetic phase space at which the different curve sections 331a/b, 332a/b and 333a/b merge together again and are connected to the common curve section 337. The time in the corresponding current profile which corresponds to the current strength at this point in the magnetic phase space within the first free-wheeling phase is then the searched-for opening time.

[0055] Moreover, the engine controller can determine, for each individual current profile 111 to 116, the work or stroke work which is performed during the opening process. This can be done by integration in the phase space along the curve sections of the first free-wheeling phase and along the curve sections of the second free-wheeling phase and by subtracting these two integration values. With knowledge of the spring constant of the solenoid drive it is then possible to determine the stroke of the fuel injector.

[0056] In summary, the method according to the invention permits in an easy way and without the use of further hardware (such as, for example, acoustic sensors or acceleration sensors) actuation of a fuel injector in which the end of the opening process and the end of the boost phase (essentially) coincide chronologically. Furthermore, an opening time and stroke work which has been performed can be determined for a selected or single current profile on the basis of the measurement data recorded in accordance with the method.

LIST OF REFERENCE NUMBERS

[0057] 101 Graphic illustration of current profiles [0058] 111 Current profile [0059] 112 Current profile [0060] 113 Current profile [0061] 114 Current profile [0062] 115 Current profile [0063] 116 Current profile [0064] 202 Graphic illustration of sound signals [0065] 221 Sound signal [0066] 222 Sound signal [0067] 223 Sound signal [0068] 224 Sound signal [0069] 225 Sound signal [0070] 226 Sound signal [0071] 303 Graphic illustration of magnetic phase space [0072] 330 Curve section [0073] 331a Curve section [0074] 331b Curve section [0075] 332a Curve section [0076] 332b Curve section [0077] 333a Curve section [0078] 333b Curve section [0079] 334 Curve section [0080] 335 Curve section [0081] 336 Curve section [0082] 337 Curve section [0083] 338 Holding state [0084] 339 Curve section [0085] 340 Curve section