DE102014218626A1 - Determining the time of a predetermined opening state of a fuel injector - Google Patents

Abstract

A method for determining the time of a predetermined opening state of a fuel injector having a fuel injector for an internal combustion engine of a motor vehicle is described. The method comprises: (a) applying a voltage pulse to the solenoid injector drive of the fuel injector to initiate an opening operation of the fuel injector; (b) detecting the time history of the voltage drop across the solenoid during a coasting phase following the application of the fuel injector to the voltage pulse and (c) determining the timing of the predetermined opening state based on the detected time history of the voltage drop. A method for driving a fuel injector, as well as a device and a motor controller, is also described.

Description

The present invention relates to the technical field of controlling fuel injectors. In particular, the present invention relates to a method for determining the time of a predetermined opening state of a fuel injector having a coil drive for an internal combustion engine of a motor vehicle. The present invention further relates to a corresponding device and a motor controller for determining the time of a predetermined opening state of a coil injector having fuel injector.

When operating fuel injectors with coil drive occurs due to electrical, magnetic, mechanical and hydraulic tolerances to different temporal opening and closing behavior of the individual injectors and thus to variations in the injection quantity.

The relative injection quantity differences from injector to injector increase with shorter injection times. So far, these relative differences in quantity were small and without practical significance. The trend towards smaller injection quantities and times, however, means that the influence of the relative quantity differences can no longer be disregarded.

Known methods for determining the actual opening and closing times are based i.a. on measurement and evaluation of the injector current. For this purpose, a shunt resistor is often mounted in the injector circuit and provided a suitable measuring device. The current measurement thus requires the use of additional hardware.

The present invention has for its object to provide a simplified and improved control of fuel injectors, which can compensate for tolerance-related relative injection quantity differences easily and effectively.

This object is solved by the subject matters of the independent claims. Advantageous embodiments of the present invention are described in the dependent claims.

According to a first aspect of the invention, a method for determining the time of a predetermined opening state of a magnetic coil drive having a fuel injector for an internal combustion engine of a motor vehicle is described. The method comprises: (a) applying a voltage pulse to the solenoid injector drive of the fuel injector to initiate an opening operation of the fuel injector; (b) detecting the time history of the voltage drop across the solenoid during a coasting phase following the application of the fuel injector to the voltage pulse and (c) determining the timing of the predetermined opening state based on the detected time history of the voltage drop.

The method described is based on the finding that the time profile of the current intensity during an opening process of the fuel injector is dependent on the inductance of the solenoid drive. In addition to the changing self-inductance of the solenoid drive (due to the non-linear ferromagnetic magnet material), a proportion of motion inductance due to the armature movement occurs. The portion of the movement inductance begins with the beginning of the opening phase (armature / needle movement begins) and ends at the end of the opening phase (armature / needle movement ends). During an electric freewheeling phase, which follows immediately after the so-called boost phase, the current passes through several components (switches, tracks, etc.) and thus the voltage can be detected directly on the solenoid drive and instead of a voltage via an additional shunt resistor can be used. As a result, no corresponding measuring channel is required for the shunt. Since the voltage across the solenoid drive is significantly greater than the voltage across a shunt resistor, the inventive method can additionally provide a better signal-to-noise ratio.

In this document, "freewheeling phase" refers to a phase in which no further electrical energy is supplied to the solenoid drive, with the coil current decreasing over time.

According to one embodiment of the invention, the duration of the voltage pulse (boost voltage) is selected such that the predetermined opening state is reached during the freewheeling phase.

In other words, the boost phase ends before the opening process is completed. Since the air gap in the injector towards the end of the boost phase is smaller, the force will still increase after switching off the boost voltage, so that the predetermined opening state during the subsequent free-running phase can be achieved.

According to a further exemplary embodiment of the invention, determining the time of the predetermined opening state comprises: (a) determining a difference profile based on the detected time profile of the voltage drop and a reference voltage drop profile and (b) determining a time at which the difference history has an extremum, the determined time being the time of the predetermined opening condition.

The reference voltage drop curve represents the voltage drop characteristic in known conditions. Consequently, at the time when the difference curve has an extremum, the difference between the detected time course of the voltage drop and the reference voltage drop curve will be maximum or minimum.

Specifically, in this document, "extremum" refers to a local or global extremum of the difference history as a function of time.

Determining the time at which the difference curve has an extreme can be carried out in particular by using numerical methods.

According to a further embodiment of the invention, the reference voltage drop curve represents the time profile of the voltage drop across the solenoid drive during a coasting phase and in a state in which the fuel injector is fixed in a predetermined position.

If the injector is fixed in a predetermined position, for example by mechanical clamping, the change in the course of the current (reference current profile) will also change as a result of the changed inductive influences. It is thus possible to determine the time of a predetermined opening state by analyzing the difference curve (the difference between the detected temporal current profile and the reference current profile).

The reference current waveform can be determined by laboratory measurements for a single fuel injector. Alternatively, the reference current waveform may be determined as the average of measurements for multiple fuel injectors.

According to a further embodiment of the invention, the predetermined position is a fully open or closed position.

If the predetermined position is the fully open position in which the armature position is fixed in a minimum air gap position (between armature and abutment surface), then the current curve (ie, the reference current path) of the fuel injector will have a temporal behavior from the beginning the energization of higher inductive behavior, since the magnetic circuit from the beginning has smaller magnetic resistances.

If the predetermined position is the closed position in which the armature position is fixed in a position with maximum air gap (between armature and abutment surface), then the current curve (that is, the reference current path) of the fuel injector exhibits a temporal behavior with less inductive behavior because the magnetic circuit has higher magnetic resistances from the beginning of the normally possible armature movement.

By determining the times at which the difference curve has an extreme, the time of the predetermined opening state of the fuel injector can now be determined in both cases. By comparing the determined time with a predetermined time, that is, a time at which the predetermined opening state should ideally be achieved, deviations from an ideal opening course of the fuel injector can be detected and optionally compensated.

According to a further exemplary embodiment of the invention, the determination of the time of the predetermined opening state comprises a mathematical analysis of the detected time profile of the voltage drop across the solenoid drive.

The mathematical analysis may be carried out in particular by numerical methods.

The mathematical analysis may serve, for example, to recognize certain patterns or states in the recorded time course of the voltage drop and to determine the corresponding points in time.

According to a further embodiment of the invention, a time is determined by the mathematical analysis, to which the detected time course and / or a derivative of which has an extremum.

According to a further exemplary embodiment of the invention, the method further comprises: (a) determining a further difference curve based on the detected time profile of the voltage and a further reference voltage curve, and (b) determining a further time point at which the further difference curve is an extreme and / or to which there is a predetermined correlation between the difference curve and the further difference curve.

In this embodiment, the reference voltage curve may correspond in particular to the fully open position of the fuel injector and the further reference voltage curve may in particular correspond to the closed position of the fuel injector. Alternatively, the reference voltage waveform may correspond to the closed position of the fuel injector and the further reference voltage waveform may correspond to the fully open position of the fuel injector.

In this exemplary embodiment, a correlation between the difference curve and the further difference curve can exist, in particular, if the two difference curves have an extreme at a substantially identical point in time. For example, such a correlation exists if the two difference curves have a local or global maximum or minimum at the same time, or if at the same time one of the difference curves has a maximum and the other difference curve has a minimum.

According to another embodiment of the invention, the detected timing of the predetermined opening state of the fuel injector is a start or end timing of an opening operation of the fuel injector.

Specifically, in this document, "fuel injector opening operation" means a course starting at the time when the closed fuel injector starts opening due to the current flowing through the coil drive and ends at the time when the fuel injector has been fully opened.

By determining the start time and the end time of the opening operation, it can be determined whether the opening operation is as it is intended. If this is not the case, for example due to tolerance-related deviations in electrical, magnetic, mechanical and hydraulic parameters of the fuel injector, the course can be compensated in order to avoid a deviation from the intended injection quantity.

According to a second aspect of the invention, a method for driving a coil injector having a fuel injector for an internal combustion engine of a motor vehicle is described. The described method comprises: (a) determining the timing of a predetermined opening state of the fuel injector by using the method according to the first aspect or one of the above embodiments, (b) determining a difference between the detected timing and a reference timing, and (c ) Driving the fuel injector, wherein the coil drive is subjected to a voltage pulse whose start time and / or time period is determined based on the determined difference.

The described method is based on the idea that the activation of the fuel injector can be adjusted based on the determined difference between the determined time and a reference time such that deviations in the injection quantity can be minimized.

Specifically, in this document, "reference timing" means a timing at which the predetermined opening state of the fuel injector should ideally arrive. The determined difference between the detected time and the reference time thus represents a measure of how much the time of actual arrival of the predetermined opening state deviates from the ideal or desired time.

If it is determined, for example, that the beginning of the opening process is shifted in time, the start time of the voltage pulse applied to the coil drive can be shifted accordingly.

For example, if it is determined that the end of the opening operation is time-shifted, the injection duration may be adjusted to ensure that the intended amount of fuel is injected. In other words, the duration of the voltage pulse may be extended in the event of a delayed opening of the fuel injector in order to avoid that too little fuel is injected. Similarly, in the event of early opening of the fuel injector, the duration of the voltage pulse may be shortened to avoid injecting too much fuel.

The above-mentioned corrections can advantageously be carried out in a pulse-individual manner, that is to say for each individual opening process.

The corrections may also take into account physical system parameters such as fuel temperature, distance to the previous injection event, and so forth. This can be done, for example, by using appropriate pilot control curves or fields or a model.

• (a) eine Beaufschlagungseinheit zum Beaufschlagen des Magnetspulenantriebs des Kraftstoffinjektors mit einem Spannungspuls, um einen Öffnungsvorgang des Kraftstoffinjektors einzuleiten, (b) eine Erfassungseinheit zum Erfassen des zeitlichen Verlaufs des Spannungsabfalls über den Magnetspulenantrieb während einer Freilaufphase, die nach dem Beaufschlagen des Kraftstoffinjektors mit dem Spannungspuls stattfindet, und (c) eine Ermittlungseinheit zum Ermitteln des Zeitpunkts des vorbestimmten Öffnungszustands basierend auf dem erfassten zeitlichen Verlauf des Spannungsabfalls.

According to a third aspect of the invention, a device for determining the time of a predetermined opening state of a magnetic coil drive having a fuel injector for an internal combustion engine of a motor vehicle is described. The device described has:

• (a) an energizing unit for energizing the solenoid of the fuel injector with a voltage pulse to initiate an opening operation of the fuel injector, (B) a detection unit for detecting the time course of the voltage drop across the solenoid drive during a freewheeling phase, which takes place after the application of the fuel injector with the voltage pulse, and (c) a determining unit for determining the time of the predetermined opening state based on the detected time course of the voltage drop.

The device described is based on the same findings as described above in connection with the first and second aspects.

The application unit has, for example, a DC-DC converter unit which can provide a boost voltage which is increased in relation to the battery voltage. The loading unit is controlled so that the boost phase is terminated by the current intensity of the current flowing through the solenoid drive reaches a predetermined value (peak current).

For example, in one embodiment, the detection unit comprises a fast-to-analog-to-digital converter (FADC) suitable for detecting the coil current of the currently operated fuel injector.

The determination unit may be advantageously implemented using a microprocessor system capable of performing the necessary mathematical operations, e.g. Difference course and extremum to determine. The system may also include a memory unit configured to store reference voltage waveforms, pilot lines, models, etc.

The device can easily determine the start and end times of an opening operation, so that the control of the respective fuel injectors can be adjusted so that relative injection quantity differences can be minimized.

According to a fourth aspect of the invention, an engine control system for an internal combustion engine of a motor vehicle is described. The described motor control is arranged to perform the methods according to the first or second aspect or one of the above embodiments.

This engine control makes it possible, with simple and inexpensive means, to minimize variations in the injection quantity in the case of several fuel injectors.

According to a fifth aspect of the invention, a computer program for determining the time of a predetermined opening state of a magnetic coil drive having a fuel injector for an internal combustion engine of a motor vehicle is described. The described computer program is set up for carrying out the methods according to the first or second aspect or one of the above exemplary embodiments, if it is executed by a μ-controller.

For the purposes of this document, the mention of such a computer program is synonymous with the notion of a program element, a computer program product, and / or a computer readable medium containing instructions for controlling a computer system to appropriately coordinate the operation of a system or method to achieve the effects associated with the method of the invention.

The computer program may be implemented as a computer-readable instruction code in any suitable programming language such as assembler, JAVA, C ++, etc. The computer program can be stored on a computer-readable storage medium (CD-ROM, DVD, Blu-ray Disc, removable drive, volatile or non-volatile memory, built-in memory / processor, etc.). The instruction code may program a computer or other programmable device such as, in particular, an engine control unit of a motor vehicle to perform the desired functions. Further, the computer program may be provided in a network, such as the Internet, from where it may be downloaded by a user as needed.

The invention can be implemented both by means of a computer program, i. software, as well as by means of one or more special electrical circuits, i. in hardware or in any hybrid form, i. using software components and hardware components.

It should be noted that embodiments of the invention have been described with reference to different subject matters. In particular, some embodiments of the invention are described with method claims and other embodiments of the invention with apparatus claims. However, it will be apparent to those skilled in the art upon reading this application that, unless explicitly stated otherwise, in addition to a combination of features associated with a type of subject matter, any combination of Characteristics is possible that belong to different types of invention objects.

Further advantages and features of the present invention will become apparent from the following exemplary description of a preferred embodiment.

The 1 shows a circuit diagram with current paths during different phases of operating a fuel injector.

The 2 Figure 12 shows an illustration of the current and voltage waveforms during various phases of fuel injector operation.

The 3 shows a flowchart illustrating a method according to an embodiment.

It should be noted that the embodiment described below represents only a limited selection of possible embodiments of the invention.

The 1 shows a circuit diagram 10 an injection system in which a fuel injector 12 is mounted with solenoid drive between the terminals HS and LS.

When the transistors Tbat and TLS are open, the fuel injector becomes 12 supplied with the battery voltage Vbat. In this state, the current runs along the path 14 , ie from Vbat through the diode Dbat, the transistor Tbat, the solenoid of the fuel injector 12 , the transistor TLS and the shunt resistor RSHUNT to ground. The shunt resistor RSHUNT is used for other functions of the system than those described here.

When the transistors Tboost and TLS are open, the fuel injector becomes 12 with the boost voltage (increased battery voltage) Vboost applied. In this state, the current runs along the path 16 , ie from Vboost through the transistor Tboost, the solenoid of the fuel injector 12 , the transistor TLS and the shunt resistor RSHUNT to ground. The shunt resistor RSHUNT is used for other functions of the system than those described here. A boost diode Dboost is provided as a backup.

If only the transistor TLS is open, for example after the end of the boost phase, a current will flow along the path 18 , ie of ground through the diode DGND, the solenoid of the fuel injector 12 , the transistor TLS and the shunt resistor RSHUNT to ground. The current path 18 corresponds to the freewheeling phase mentioned in this document.

The 2 shows an illustration 20 the courses of current 22 and tension 24 during various phases of operating a fuel injector. At time T0, the boost voltage is turned on. The voltage 24 via the injector increases accordingly and the current strength 22 rises. At time T1, the current reaches a predetermined value (peak current value) and the boost voltage is switched off again. The time T1 therefore corresponds to the end of the boost phase and the beginning of the subsequent freewheeling phase, in which the current decreases again. The freewheeling phase ends at the time T2, in that the current has fallen to a further predetermined value. After T2 follows a so-called holding phase, in which the coil current 22 is maintained within a certain range by applying several small voltage pulses to keep the fuel injector open. At time T3, the closing operation of the fuel injector is initiated.

The 3 shows a flowchart 30 , which illustrates a method according to an embodiment. The method will now be with reference to the circuit diagram 10 in 1 described.

In step 32 the solenoid actuator of the fuel injector is subjected to a voltage pulse (boost voltage) to an opening operation of the fuel injector 12 initiate. When the predetermined peak current value is reached, the boost voltage is switched off. In step 34 Now the time course of the voltage drop across the solenoid drive is detected during a freewheeling phase, which takes place after the application of the fuel injector with the voltage pulse. In step 36 the time of the predetermined opening state is determined based on the detected time profile of the voltage drop. As described above, the determination of the time point may inter alia include a mathematical analysis of the detected time profile and / or a determination of a difference profile based on the detected time profile and a reference voltage profile.

As a result, it can be achieved in a simple and cost-effective manner that each fuel injector delivers the predetermined injection quantity per injection process with great accuracy, so that no or only very small relative differences in quantity can occur between the injectors.

The necessary compensation takes place in a simple manner by shifting the activation of the boost voltage and / or lengthening or shortening the injection duration. As a result, no changes in the current profiles are required per se during the opening process.

LIST OF REFERENCE NUMBERS

10

 circuit diagram

12

 fuel injector

14

 Rung path (battery)

16

 Current path (boost phase)

18

 Current path (free-running phase)

Vbat

 battery voltage

DBAT

 diode

Tbat

 transistor

vboost

 boost voltage

TBOOST

 transistor

Dboost

 diode

DGND

 diode

HS

 connection

LS

 connection

TLS

 transistor

RSHUNT

 Shunt resistor

20

 Illustration

22

 amperage

24

 tension

T0

 time

T1

 time

T2

 time

T3

 time

30

 flow chart

32

 step

34

 step

36

 step

Claims (10)

Method for determining the time of a predetermined opening state of a fuel injector having a solenoid actuator ( 12 ) for an internal combustion engine of a motor vehicle, the method comprising ( 32 ) of the solenoid of the fuel injector with a voltage pulse to initiate an opening operation of the fuel injector, detecting ( 34 ) of the time course of the voltage drop across the solenoid drive during a freewheeling phase, which takes place after the application of the fuel injector with the voltage pulse, and determining ( 36 ) of the timing of the predetermined opening state based on the detected time history of the voltage drop. Method according to the preceding claim, wherein the time duration of the voltage pulse is selected such that the predetermined opening state is reached during the freewheeling phase. The method of any one of the preceding claims, wherein determining the time of the predetermined opening condition comprises: Determining a difference profile based on the detected time course of the voltage drop and a reference voltage drop curve and Determining a time at which the difference curve has an extremum, wherein the determined time is the time of the predetermined opening state. A method according to the preceding claim, wherein the reference voltage drop curve represents the time course of the voltage drop across the solenoid drive during a coasting phase and in a state in which the fuel injector is fixed in a predetermined position. A method according to the preceding claim, wherein the predetermined position is a fully open or closed position. The method of claim 1 or 2, wherein determining the time of the predetermined opening state comprises a mathematical analysis of the detected time history of the voltage drop across the solenoid drive. Method according to the preceding claim, wherein the mathematical analysis determines a time at which the detected time course and / or a derivative thereof has an extremum. A method of driving a coil injector having a fuel injector for an internal combustion engine of a motor vehicle, the method comprising Determining the time of a predetermined opening state of the fuel injector by using the method according to one of the preceding claims, Determining a difference between the determined time and a reference time, and Driving the fuel injector, wherein the coil drive is subjected to a voltage pulse whose start time and / or time period is determined based on the determined difference. Device for determining the time of a predetermined opening state of a fuel injector having a fuel injector for an internal combustion engine of a motor vehicle, the device comprising a loading unit for applying the magnetic coil drive of the fuel injector with a voltage pulse to initiate an opening operation of the fuel injector, a detection unit for detecting the time history of the voltage drop across the solenoid drive during a coasting phase that takes place after the fuel injector is applied with the voltage pulse, and a determination unit for determining the timing of the predetermined opening state based on the detected time course of the voltage drop. Engine control for an internal combustion engine of a motor vehicle, wherein the engine control is arranged to perform the method according to one of claims 1 to 8.

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