Method for determining an opening delay of a fuel injector

Abstract

A method is described for determining an opening delay of a fuel injector in which by activating a solenoid with the aid of an armature, a valve needle may be opened wherein a mathematical model is used which includes an activation duration of the solenoid as an input variable and a respective opening delay as an output variable.

Claims

1. A method for determining an opening delay time of a fuel injector, comprising: performing a fuel injection with the fuel injector by opening a valve needle, the valve needle being opened by activating a solenoid with the aid of an armature; wherein the fuel injection is performed based on a mathematical model which includes an activation duration of the solenoid as an input to the mathematical model and an opening delay time as an output variable of the mathematical model, the opening delay time being determined as a function of the input activation duration using the mathematical model, wherein the fuel injector includes a stop of a valve needle and a stop sleeve of the valve needle, wherein the armature is movable between the stop and the stop sleeve, wherein in a resting position of the armature, there is a gap between an upper edge of the armature and a lower edge of the stop, the gap being an armature free path, and when the armature reaches the solenoid or a housing surrounding the solenoid or another stop, the armature does not move further while the valve needle does move further upward.

2. The method as recited in claim 1, wherein an open duration of the fuel injector that is necessary for an amount of fuel to be introduced with the fuel injector is ascertained by taking into account an activation duration of the solenoid, the determined opening delay time, and a closing delay time, wherein the fuel injection is performed based on the ascertained open duration.

3. The method as recited in claim 1, wherein: the mathematical model is adapted to a fuel injector for which the mathematical model is to be used by ascertaining at least one of: a respective opening delay time for at least one activation duration of the solenoid, a current profile in the solenoid, and a voltage profile in the solenoid, and the mathematical model is adapted so that based on the mathematical model one of the respective opening delay time, the current profile, and the voltage profile is obtained from the at least one activation duration.

4. The method as recited in claim 3, wherein the adapting of the mathematical model includes specifying a parameter of a parameterizable function.

5. The method as recited in claim 4, wherein at least one of a minimum activation duration at which the valve needle is just opening and a shorter activation duration than the minimum activation duration is used for specifying the parameter of the function.

6. The method as recited in claim 5, wherein, for ascertaining the minimum activation duration, the activation duration is increased incrementally starting with an activation duration at which the valve needle does not open.

7. The method as recited in claim 3, wherein the mathematical model is adapted by ascertaining at least one opening delay time and by taking into account at least one of the current profile and the voltage profile.

8. The method as recited in claim 3, wherein the mathematical model is adapted by ascertaining at least opening delay time and by taking into account a pressure profile in a respective fuel distribution system at a maximum lift of the valve needle.

9. The method as recited in claim 3, wherein the mathematical model is ascertained by ascertaining a respective opening delay time for various activation durations of the solenoid, and by using a relationship between the activation durations of the solenoid and the respective opening delay times as the mathematical model.

10. The method as recited in claim 9, wherein the mathematical model is a function, the function is a parameterizable function that indicates the opening delay time as a function of the activation duration of the solenoid and that is ascertained from the relationship between the activation durations of the solenoid and the respective opening delay times.

11. The method as recited in claim 10, wherein the function is ascertained from corresponding relationships for several identical fuel injectors.

12. The method as recited in claim 10, wherein at least one of at least one characteristic map and at least one characteristic line is the function.

13. The method as recited in claim 1, wherein in the mathematical model a dependence of the opening delay time on a pressure with which a fuel is supplied to the fuel injector is taken into account with a dependence of the activation duration on the pressure.

14. A computer unit for determining an opening delay time of a fuel injector, comprising: a processor configured to perform the following: performing a fuel injection with the fuel injector by opening a valve needle, the valve needle being opened by activating a solenoid with an armature; wherein the fuel injection is performed based on a mathematical model which includes an activation duration of the solenoid as an input to the mathematical model and an opening delay time as an output variable of the mathematical model, the opening delay time being determined as a function of the input activation duration using the mathematical model, wherein the fuel injector includes a stop of a valve needle and a stop sleeve of the valve needle, wherein the armature is movable between the stop and the stop sleeve, wherein in a resting position of the armature, there is a gap between an upper edge of the armature and a lower edge of the stop, the gap being an armature free path, and when the armature reaches the solenoid or a housing surrounding the solenoid or another stop, the armature does not move further while the valve needle does move further upward.

15. A non-transitory computer readable medium having a computer program, which is executable by a processor, comprising: a program code arrangement having program code for determining an opening delay time of a fuel injector, by performing the following: performing a fuel injection with a fuel injector by opening a valve needle, the valve need being opened by activating a solenoid with an armature; wherein the fuel injection is performed based on a mathematical model which includes an activation duration of the solenoid as in input to the mathematical model and an opening delay time as an output variable, the opening delay time being determined as a function of the input activation duration using the mathematical model, wherein the fuel injector includes a stop of a valve needle and a stop sleeve of the valve needle, wherein the armature is movable between the stop and the stop sleeve, wherein in a resting position of the armature, there is a gap between an upper edge of the armature and a lower edge of the stop, the gap being an armature free path, and when the armature reaches the solenoid or a housing surrounding the solenoid or another stop, the armature does not move further while the valve needle does move further upward.

16. The computer readable medium of claim 15, wherein an open duration of the fuel injector that is necessary for an amount of fuel to be introduced with the fuel injector is ascertained by taking into account an activation duration of the solenoid, the determined opening delay time, and a closing delay time, wherein the fuel injection is performed based on the ascertained open duration.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1A schematically shows a detail of a fuel injector including a solenoid valve and an armature free path, with the aid of which a method according to the present invention may be carried out in a preferred specific embodiment in various positions during operation.

(2) FIG. 1B schematically shows a detail of a fuel injector including a solenoid valve and an armature free path, with the aid of which a method according to the present invention may be carried out in a preferred specific embodiment in various positions during operation.

(3) FIG. 1C schematically shows a detail of a fuel injector including a solenoid valve and an armature free path, with the aid of which a method according to the present invention may be carried out in a preferred specific embodiment in various positions during operation.

(4) FIG. 1D schematically shows a detail of a fuel injector including a solenoid valve and an armature free path, with the aid of which a method according to the present invention may be carried out in a preferred specific embodiment in various positions during operation.

(5) FIG. 1E schematically shows a detail of a fuel injector including a solenoid valve and an armature free path, with the aid of which a method according to the present invention may be carried out in a preferred specific embodiment in various positions during operation.

(6) FIG. 1F schematically shows a detail of a fuel injector including a solenoid valve and an armature free path, with the aid of which a method according to the present invention may be carried out in a preferred specific embodiment in various positions during operation.

(7) FIG. 2 shows profiles for the armature and valve needle lift in the case of a fuel injector including a solenoid valve and an armature free path, as shown in FIGS. 1A through 1F.

(8) FIG. 3 shows various armature lift profiles for a fuel injector including a solenoid valve and an armature free path when a method according to the present invention is carried out.

(9) FIG. 4 shows a relationship between the opening delay and the activation duration as is ascertainable using a method according to the present invention.

DETAILED DESCRIPTION

(10) FIG. 1A schematically shows a detail of a fuel injector 100. A valve needle 110 is provided to close fuel injector 100 in a resting state so that no fuel from fuel injector 100 reaches the internal combustion engine. For this purpose, valve needle 110 closes a valve seat 170 in that valve needle 110 is acted on by a force with the aid of a closing spring 150.

(11) In addition, in a typical fuel injector 100, a fuel pressure of a fuel which prevails in fuel injector 100 and in particular also at the top side of valve needle 110 also acts through an appropriate design in the direction of the spring force of closing spring 150.

(12) Moreover, a solenoid 140 and an armature 130 are provided. Solenoid 140 is situated in a stationary position in fuel injector 100, while armature 130 is movable in the longitudinal direction of valve needle 110. For this purpose, a hole having a diameter slightly larger than the diameter of valve needle 110 is provided in armature 130, for example. The activation of fuel injector 100 and thus of solenoid 140 may take place with the aid of a computer unit 190, for example an engine control unit.

(13) In the resting state armature 130 rests on a stop sleeve 160 fixedly connected to the valve needle. As soon as solenoid 140 is energized, i.e., activated, armature 130 is moved from its resting position by a magnetic force in the direction of solenoid 140, as indicated by an arrow in FIG. 1A. Armature 130 thus passes initially through a so-called armature free path.

(14) A stop 120 is formed on valve needle 110. Stop 120 may be designed to be integral with valve needle 110, for example, or as an add-on part fixedly connected to valve needle 110. The diameter of stop 120 is larger than the diameter of the hole in armature 130. In the resting position of armature 130, a gap is provided between the upper edge of armature 130 and the lower edge of stop 120, namely the above mentioned so-called armature free path.

(15) As soon as armature 130 has reached stop 120 during the activation of solenoid 140, as shown in FIG. 1B, valve needle 110 is moved together with armature 130 in the opening direction against the force of closing spring 150. This is indicated by an additional arrow at valve needle 110.

(16) When armature 130 reaches solenoid 140 (or a housing surrounding solenoid 140 or some other stop), then armature 130 does not move further while valve needle 110 does move somewhat further upward as shown in FIG. 1C.

(17) Subsequently, valve needle 110 strikes armature 130 with stop 120 after a brief movement in the closing direction, as shown in FIG. 1D. After the end of the activation of solenoid 140, armature 130 moves in the closing direction due to the now absent magnetic force. Valve needle 110 also moves in the closing direction.

(18) Ultimately, valve needle 110 reaches valve seat 170 and closes it, as shown in FIG. 1E. Armature 130 passes through the armature free path, as indicated by an arrow, in the direction of stop sleeve 160. Subsequently, armature 130 rests on stop sleeve 160 and is again in the resting position as shown in FIG. 1F. It is possible here that armature 130 bounces once or several times on stop sleeve 160 and is hydraulically attenuated in the process.

(19) FIG. 2 shows the profiles of armature lift h.sub.M and valve needle lift h.sub.V in a routine injection process with passage through the positions, plotted over time t, shown in FIGS. 1A to 1F. For this purpose, reference notations a through f show time segments in which the corresponding position illustrated in FIGS. 1A through 1E is situated.

(20) At the start of the energization or activation of solenoid 140, armature 130 moves from resting position h.sub.M,0 in the direction of stop 120. After passing through the armature free path, armature 130 entrains valve needle 110 from the resting position h.sub.V,0 of the stop of the valve needle in its upward movement, which results in the opening of valve needle 110 and thus the injection operation.

(21) At the end of time segment b armature 130 reaches solenoid 140 and thus a maximum lift h.sub.P. Valve needle 110 however moves somewhat further and falls back. Toward the end of time segment c, valve needle 110 reaches armature 130 and rests on it.

(22) At the end of time segment d, the activation of solenoid 140 then ends and thus activation duration t.sub.A also ends. After a short period of time of sticking on solenoid 140, armature 130 and with it the valve needle begins to move in the closing direction. Toward the end of time segment e valve needle 110 has reached the valve seat while the armature is still bouncing.

(23) FIG. 3 shows various armature lift profiles h.sub.M,1 through h.sub.M,7 as a function of time t in a fuel injector including a solenoid valve and an armature free path such as that shown in FIGS. 1A through 1F for example, in a preferred specific embodiment when a method according to the present invention is carried out.

(24) Armature lift profiles h.sub.M,1 through h.sub.M,7 correspond to activation durations which always increase further beginning with index 1 up to index 7. All armature lift profiles have in common the fact that the armature begins to lift only after a certain period of time, namely here from point in time t.sub.0. Before that the armature remains in its resting position (so-called armature sticking) due to hydraulic forces.

(25) It is apparent from armature lift profiles h.sub.M,1 and h.sub.M,2, that the armature has in fact reached the stop of the valve needle, i.e., resting position h.sub.V,0 of the stop of the valve needle, but the valve needle is not yet lifted.

(26) Only with the activation duration underlying armature lift profile h.sub.M,3 the valve needle is opened. Point in time t.sub.1 at which the valve needle opens thus defines opening delay t.sub.O belonging to the activation duration which belongs to armature lift profile h.sub.M,3. Longer activation durations result in higher magnetic forces and shorter opening delays.

(27) Moreover, it is apparent that the minimum opening delay, which continues up to point in time t.sub.2, is reached with armature lift profile h.sub.M,6 or the respective activation duration. No shorter opening delay is obtained with armature lift profile h.sub.M,7 although the so-called full lift, i.e., the maximum opening of the valve needle, is already achieved here.

(28) FIG. 4 shows a relationship between opening delay t.sub.O and activation duration t.sub.A, such as that which is ascertainable in a preferred specific embodiment with a method according to the present invention.

(29) According to the armature lift profiles shown in FIG. 3 and their respective activation durations, respective opening delays may be ascertained, for example, for various activation durations (corresponding to various armature lift profiles). For example, this may involve the activation durations represented by armature lift profiles h.sub.M,3 and h.sub.M,2.

(30) This reveals a relationship between opening delay t.sub.O and activation duration t.sub.A such as that illustrated here with the aid of the line or function f. In particular, activation duration t.sub.A,1 belonging to time t.sub.1 according to FIG. 3 is shown with the opening delay, and the activation duration t.sub.A,2 belonging to time t.sub.2 according to FIG. 3 is shown with the opening delay. While the former corresponds to the initial opening of the valve needle, the latter indicates the occurring minimal opening delay. Function f may be ascertained from individual measuring points by suitable interpolation for example.

(31) Function f ascertained in this way may now be used as a mathematical model for ascertaining an open duration of a fuel injector, as described at the outset.

(32) The mathematical model obtained in this way may now be adapted individually to a certain fuel injector. For this purpose, the minimum activation duration at which the valve needle opens may be ascertained for the specific fuel injector according to the armature lift profiles h.sub.M,1 through h.sub.M,3 shown in FIG. 3.