DE102017206366A1 - Method for operating a fuel injector - Google Patents

Abstract

The invention relates to a method for operating a fuel injector. Herein, during a fuel injection, a holding current level (I _h ) of the fuel injector is reduced to a drop level (I _a ). In this case, the armature stroke (A) of the fuel injector drops to a seat throttle limit.

Description

The present invention relates to a method of operating a fuel injector. Furthermore, the present invention relates to a computer program which is set up to carry out each step of the method according to the invention and to a machine-readable storage medium on which the computer program according to the invention is stored. Finally, the invention relates to an electronic control device, which is set up to operate a fuel injector by means of the method.

State of the art

For the operation of a fuel injector for the common-rail direct injection, a certain allowance must be taken into account in the armature stroke adjustment. This ensures that the armature stroke in critical operating situations, such as low temperatures or a pressure jump is not too low and a seat throttling can be reliably prevented. In normal operation, the fuel injector is consequently operated at a holding current level which generates an unnecessarily high armature stroke for the injector function. This can lead to increased wear as they increase with increasing armature stroke. The reason for this is the low valve chamber pressure associated with a high armature stroke. This applies primarily to main injections, because with short activation periods, as they occur during pre- and post-injections, the valve-chamber pressure is not lowered so much and therefore hardly any damage occurs.

An inference to the armature stroke is possible by evaluating the signal of a piezoelectric needle closing sensor (NCS).

The use of such a piezoelectric needle closing sensor is in DE 10 2014 204 098 A1 described.

Disclosure of the invention

In the method of operating a fuel injector, a hold current level of the fuel injector is reduced to a drop level during fuel injection. This drop level is selected so that an armature stroke of the fuel injector drops to a seat throttle limit. This makes it possible to reduce the effective armature lift to the armature lift level which is still permissible for the injector function. This reduction leads to an effective increase of a valve space pressure of the fuel injector and thus to a reduction of the wear. In particular, the fuel injector is a common rail fuel injector for direct fuel injection.

In one embodiment, it is preferable that a drive duration of the fuel injector be extended so that a valve opening duration of the fuel injector remains unchanged from operation with only the holding current level and the original drive duration. A reduced valve closing time due to the reduced armature stroke at the moment of the current cut-off of the holding current is thus compensated by an adaptation of the activation duration in order to keep the valve opening duration constant. In particular, the control function VCC (Variable Compression Control) can be used for this purpose.

In another embodiment, it is preferable that the holding current level during the fuel injection is increased again to its initial value. As a result, the anchor is pulled back to the stroke stop before closing. Again, the level of the waste stream is chosen so that the anchor just never falls below the seat throttle limit. The safe achievement of the stroke stop can be ensured in particular by monitoring the valve closing duration by means of VCC or by means of the signal of a piezoelectric needle closing sensor, as shown in the DE 10 2014 204 098 A1 is described. This embodiment has the advantage that the valve closing duration does not change and thus also the activation duration of the fuel injector does not have to be readjusted in order to keep the valve opening duration constant.

In addition to the level of the current level, a period until a switchover from the holding current to the waste stream can be set in order to achieve that the armature stroke drops to exactly the seat throttle limit value. Should a free choice of the holding current level not be possible, a drop of the armature over the time of the current switching from the holding current to the waste stream can be set. This may be necessary, for example, if only a limited number of fixed current levels can be implemented in a control unit which controls the fuel injector.

The level of the waste stream is understood to mean a time-averaged current level. This can be realized not only by a constant current, but also for example by a pulsed current.

The fuel injection is preferably a main fuel injection. Here, a significant reduction of the wear can be achieved by the method, while the method is based on and post-injections does not significantly reduce wear.

Basically, the armature stroke by the evaluation of the signal of a piezoelectric Nadelschließsensors according to the DE 10 2014 204 098 A1 be determined. Due to the not exactly known piezoelectric properties of the needle-closing sensor, however, this method is inaccurate. It is therefore preferred that during opening of a switching valve of the fuel injector, a total signal drop of a piezoelectric needle closing sensor of the fuel injector and a signal drop within the total signal drop are determined and determined from a ratio between the total signal drop and the signal dip the armature stroke.

The total signal drop can be determined, in particular, as the difference between an electrical signal of the needle-closing sensor when the switching valve is closed and a local minimum of the electrical signal of the needle-closing sensor when the switching valve is open. The electrical signal of the needle closing sensor with closed switching valve is ideally zero. By compression of the piezoelectric element of the needle closing sensor when opening the switching valve, a negative electrical signal is generated.

The signal collapse is determined in particular as the difference between the local minimum of the electrical signal of the needle-closing sensor when the switching valve is open and a local maximum of the electrical signal of the needle-closing sensor when the switching valve is open.

The electrical signal may be a voltage applied to the piezoelectric element. If the piezoelectric element is connected via a low-resistance resistor, the current delivered by the piezoelectric element can be used as the electrical signal instead of the voltage.

Determining the anchor stroke is preferably carried out by means of a characteristic which describes the dependence of the ratio of the armature stroke. Such a characteristic curve can be easily generated from theoretical considerations or from empirical measurements.

From an end point of fuel injection, it may be optionally concluded whether the armature stroke has dropped below the seat throttle limit during fuel injection. This allows a subsequent Ankerhubüberwachung. In addition to the monitoring, an adjustment of the current supply is possible in particular, so that the armature just does not sink below the seat throttle value. In this case, in the sense of an active control either the waste stream can be raised or the switching from the holding current to the waste stream takes place later.

The computer program is set up to perform each step of the method, in particular when it is performed on an electronic computing device or controller. For this purpose it is stored on the machine-readable storage medium. The computer program allows the simple implementation of the method in an existing control unit, without having to make structural changes. By loading the computer program onto a conventional electronic control unit, the electronic control unit is set up, which is set up to operate a fuel injector.

list of figures

• 1 zeigt in einem Diagramm den zeitlichen Verlauf des Ventilraumdrucks eines Kraftstoffinjektors für verschiedene Einspritzungsarten.
• 2 zeigt in drei Diagrammen den zeitlichen Verlauf eines zeitlichen Stromverlaufs und Ankerhubverlaufs eines Kraftstoffinjektors, sowie den zeitlichen Verlauf eines Nadelschließsensorsignals in einem Ausführungsbeispiel des erfindungsgemäßen Verfahrens.
• 3 zeigt in drei Diagrammen den zeitlichen Verlauf eines zeitlichen Stromverlaufs und Ankerhubverlaufs eines Kraftstoffinjektors, sowie den zeitlichen Verlauf eines Nadelschließsensorsignals in einem anderen Ausführungsbeispiel des erfindungsgemäßen Verfahrens.
• 4 zeigt in drei Diagrammen den zeitlichen Verlauf eines zeitlichen Stromverlaufs und Ankerhubverlaufs eines Kraftstoffinjektors, sowie den zeitlichen Verlauf eines Nadelschließsensorsignals in noch einem anderen Ausführungsbeispiel des erfindungsgemäßen Verfahrens.
• 5 zeigt in drei Diagrammen den zeitlichen Verlauf eines zeitlichen Stromverlaufs und Ankerhubverlaufs eines Kraftstoffinjektors, sowie den zeitlichen Verlauf eines Nadelschließsensorsignals in noch einem anderen Ausführungsbeispiel des erfindungsgemäßen Verfahrens.
• 6 zeigt in einem Diagramm die zeitlichen Verläufe von Spannungssignalen eines Nadelschließsensors eines Kraftstoffinjektors für unterschiedliche Ankerhübe.
• 7 zeigt in einem Diagramm die Abhängigkeit eines Verhältnisses eines Gesamtsignalabfalls und eines Signaleinbruchs vom Ankerhub in Ausführungsbeispielen des erfindungsgemäßen Verfahrens.

Embodiments of the invention are illustrated in the drawings and explained in more detail in the following description.

• 1 shows a diagram of the time course of the valve chamber pressure of a fuel injector for different types of injection.
• 2 shows in three diagrams the time course of a time course of current and Ankerhubverlaufs a fuel injector, and the time course of a Nadelschließsensorsignals in an embodiment of the method according to the invention.
• 3 shows in three diagrams the time course of a time course of current and Ankerhubverlaufs a fuel injector, and the time course of a Nadelschließsensorsignals in another embodiment of the method according to the invention.
• 4 shows in three diagrams the time course of a time course of current and Ankerhubverlaufs a fuel injector, and the time course of a Nadelschließsensorsignals in yet another embodiment of the method according to the invention.
• 5 shows in three diagrams the time course of a time course of current and Ankerhubverlaufs a fuel injector, and the time course of a Nadelschließsensorsignals in yet another embodiment of the method according to the invention.
• 6 shows a diagram of the time courses of voltage signals of a needle closing sensor of a fuel injector for different armature strokes.
• 7 shows in a diagram the dependence of a ratio of a total signal drop and a signal drop from the armature stroke in embodiments of the method according to the invention.

Embodiments of the invention

Embodiments of the method according to the invention can be used to operate a fuel injector consisting of DE 10 2009 029 549 A1 is known. This document is fully incorporated by reference into these embodiments.

The valve chamber pressure of the fuel injector is discharged by means of a guide rod to a small piezoelectric element as a needle closing sensor. A voltage provided by the needle-closing sensor can be read out as an electrical signal. This is less an offset voltage proportional to the valve chamber pressure. The read electrical signal is passed to a control unit which controls the fuel injector.

The change of the valve space pressure p with the time t is for a conventional operation of the fuel injector in 1 shown. This results in a preinjection VE, a main injection HE and a post-injection NE different pressure profiles. Only in the case of the main injection HE does the valve space pressure p drop below a critical pressure level p _k for a relatively long period of time, which can lead to increased wear of the fuel injector. The exemplary embodiments of the method according to the invention described below show possibilities of how the fuel injector in the main injection HE can be controlled such that the valve space pressure p does not fall below the critical pressure level p.

In a first embodiment, the energization of the fuel injector as shown in FIG 2 modified. In the upper part of the figure, the course of the electrical current I is shown in a conventional operating strategy with a solid line and the inventively provided current waveform is shown with a dotted line. Both in the conventional and in the operating strategy according to the invention, the current I first rises to a maximum as a boost / starting current and then drops to a holding current level I _h . As in the middle part of the 2 is shown, this increases the armature stroke A of the fuel injector also to a maximum, which corresponds to a maximum raised armature and thus a fully open needle valve of the fuel injector. Only with shutdown of the current I at the end of the main injection sinks the armature stroke A and the needle valve closes. By contrast, the method according to the invention provides that the holding current level I _h is lowered to a waste level I _a before the end of the main injection. This is chosen so that the armature stroke A drops to a seat throttle limit A _s , but this does not fall below during the main injection. Only when switching off the current I, the armature stroke A falls below the seat throttle limit A _s . The armature stroke is monitored via the voltage signal NCS of the needle closing sensor. In this case, a limit value NCS _{s of} the voltage signal indicates when the seat throttle limit value A _{s is} reached.

In a second embodiment, the energization of the fuel injector as shown in FIG 3 modified. The inventive method provides that the waste level I _{a is} not chosen as low as in the first embodiment. This may be necessary if the current level is not infinitely adjustable, but only a few current levels are specified in the control unit. In order to achieve that the armature stroke A drops to the seat throttle limit A _s until the end of the main injection, the current I is lowered earlier to the waste level I _a , than is provided in the first exemplary embodiment of the method according to the invention. When the current I is switched off, the armature stroke also drops below the seat throttle limit value A _s in the second exemplary embodiment.

In a third embodiment, the energization of the fuel injector as shown in FIG 4 modified. This embodiment differs from the second embodiment in that the waste level I _{a is} not realized by a constant current supply but by a pulsed current supply.

In a fourth embodiment, the energization of the fuel injector as shown in FIG 5 modified. The inventive method provides that the waste level I _a is chosen to be as low as in the second embodiment. However, the reduction to the waste level I _a takes place even earlier than in the second embodiment. If it were left unchanged until the end of the main injection, this would mean that the armature stroke A still falls below the seat throttle limit value A _s during the main injection. Even before the seat throttle limit A _{s is} reached, the current I, therefore again raised to the holding current level I _h . It achieves this when the armature stroke A reaches the seat throttle limit value A _s , so that it can not sink further, but rises again to its maximum value until the end of the main injection.

In 6 the time profile of the voltage signal NCS for different armature strokes A ₁ to A _{5 is} shown, with A ₁ the lowest armature stroke and A ₅ corresponds to the highest anchor stroke. Starting from a signal of 0 V, the voltage signal NCS falls when turning on the current I each to a local minimum. This waste is referred to as the total signal drop G. When the current I is turned off, the electrical signal U rises again to its initial value. In the electrical voltage signal NCS, a pause of the armature movement as signal collapse S is recognizable. As the armature stroke decreases, the severity of the signal dip S increases.

The total signal drop G corresponds to the quotient of the theoretical total signal drop Gt by the piezoelectric longitudinal effect d ₃₃ . The signal drop S corresponds to the quotient of the theoretical signal drop St by the piezoelectric longitudinal effect d ₃₃ . Both depend on the armature stroke. The theoretical total signal drop G _t and the theoretical signal drop S _t denote the values of the total signal drop G and of the signal drop S that are independent of the piezoelectric longitudinal effect d ₃₃ . The ratio V of the theoretical total signal drop S _g and the theoretical signal drop S _s is given by Formula 1: $$V=\frac{S}{G}=\frac{\raisebox{1ex}{$S_t$}\!\left/ \!\raisebox{-1ex}{$d_{33}$}\right.}{\raisebox{1ex}{$G_t$}\!\left/ \!\raisebox{-1ex}{$d_{33}$}\right.}=\frac{S_t}{G_t}$$

Thus the ratio V is not dependent on the piezoelectric longitudinal effect d _33rd It is in 7 represented as a function of armature stroke A. This dependence between the armature stroke A and the ratio V is stored as a characteristic in the control unit. After calculating the ratio V, therefore, the armature stroke A can be determined. It can also be determined at which limit value NCS _{s of} the voltage signal the armature stroke A reaches the seat throttle limit value A _s .

From an end point of the fuel injection is further concluded whether the armature lift A has dropped below the seat throttle limit A _s during the main injection. As a result, a subsequent Ankerhubüberwachung also takes place.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102014204098 A1 [0004, 0007, 0011]
• DE 102009029549 A1 [0019]

Claims (9)

A method of operating a fuel injector, wherein during a fuel injection, a holding current level (I _h ) of the fuel injector is reduced to a drop level (I _a ) at which the armature lift (A) of the fuel injector drops to a seat throttle limit. Method according to Claim 1 , characterized in that a drive duration of the fuel injector is extended so that a valve opening duration of the fuel injector remains unchanged from operation with the holding current level (I _h ) and the original drive duration. Method according to Claim 1 , characterized in that the waste level (I _a ) is increased again during the fuel injection to the holding current level (I _h ). Method according to one of Claims 1 to 3 , characterized in that the fuel injection is a main fuel injection (HE). Method according to one of Claims 1 to 4 characterized in that during opening of a switching valve of the fuel injector, a total signal drop (G) of a piezoelectric needle closing sensor of the fuel injector and a signal dip (S) within the total signal drop (G) are determined and from a ratio (V) between the total signal drop (G) and the signal drop (S) of the armature stroke (A) is determined. Method according to one of Claims 1 to 5 , characterized in that it is concluded from an end time of the fuel injection, whether the armature stroke (A) during the fuel injection below the seat throttle limit (A _s ) has dropped. Computer program, which is set up, each step of the procedure according to one of Claims 1 to 6 perform. Machine-readable storage medium on which a computer program is based Claim 7 is stored. An electronic control unit adapted to operate a fuel injector by a method according to any one of Claims 1 to 6 to operate.

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