Detecting a predetermined opening state of a fuel injector having a solenoid drive

Abstract

Method for determining a time at which a fuel injector having a solenoid drive for an internal combustion engine of a motor vehicle is in a predetermined opening state, the method comprising Applying (710) a predetermined electrical voltage profile to the solenoid drive, detecting (720) the time course of the current intensity of a current flowing through the coil of the solenoid drive, Detecting (730) the time course of the voltage across the coil, Determining (740) a function based on the time course of the current intensity and the time course of the voltage, wherein the function represents the linked magnetic flux or a time derivative of the linked magnetic flux in the solenoid drive, and Determining (750) the time as the time at which the function has a characteristic feature.

Description

[0001] The present invention relates to the technical field of fuel injector control. In particular, the present invention relates to a method for determining a point in time at which a fuel injector having a solenoid drive for an internal combustion engine of a motor vehicle is in a predetermined opening state. The present invention further relates to a method for controlling a fuel injector having a solenoid drive, wherein the control is based on a point in time determined according to the invention. The present invention further relates to an engine control system and a computer program configured to carry out the method according to the invention.

[0002] A fuel injector, such as a solenoid valve or solenoid injector, can be used to inject fuel into a combustion chamber, such as a cylinder. Such a solenoid injector (also called a coil injector) has a coil which, when current flows through the coil, generates a magnetic field. This exerts a magnetic force on an armature, causing the armature to move and open or close a nozzle needle or closure element to open or close the solenoid valve. If the solenoid valve or solenoid injector has a so-called idle stroke between the armature and nozzle needle, or between the armature and closure element, a displacement of the armature does not immediately cause the closure element or nozzle needle to move, but only after the armature has moved by the amount of the idle stroke.

[0003] When voltage is applied to the coil of the solenoid valve, electromagnetic forces move the armature towards a pole piece or pole shoe. Due to a mechanical coupling (e.g. a mechanical contact), the nozzle needle or the closing element also moves after overcoming the idle stroke and, with appropriate displacement, opens injection holes for supplying fuel to the combustion chamber. If current continues to flow through the coil, the armature and nozzle needle or closing element continue to move until the armature reaches or strikes the pole piece. The distance between the armature striking a driver of the closing element or the nozzle needle and the armature striking the pole piece is also known as the needle stroke or working stroke. To close the fuel injector, the excitation voltage applied to the coil is switched off and the coil is briefly closed so that the magnetic force is dissipated.The coil short circuit causes a voltage reversal due to the dissipation of the magnetic field stored in the coil. The voltage level is limited by a diode. Due to a restoring force, provided, for example, by a spring, the nozzle needle or closure element, including the armature, is moved into the closed position. The idle stroke and the needle stroke are performed in reverse order. With short injection times, the closing process begins even before the armature hits the pole piece, so the needle movement follows a ballistic trajectory.

[0004] The point in time at which needle movement begins when the fuel injector opens (also called OPP1) corresponds to the start of injection, and the point in time at which needle movement ends when the fuel injector closes (also called OPP4) corresponds to the end of injection. These two points in time thus determine the hydraulic duration of injection. Injector-specific temporal variations in the start of needle movement (opening) and the end of needle movement (closing) can therefore result in different injection quantities with identical electrical control.

[0005] According to the state of the art, the above-mentioned (and other relevant) times corresponding to specific opening states can be determined in various ways. These times are usually determined based on the eddy current-driven coupling between the mechanical system (armature and injector needle) and the magnetic circuit (coil), which generates a feedback signal based on the movement of the mechanical system. A speed-dependent eddy current is induced in the armature as a result of the movement of the nozzle needle and armature, which also causes a feedback effect on the electromagnetic circuit. Depending on the speed of movement, a voltage is induced in the electromagnet, which is superimposed on the control signal. Exploiting this effect requires that the superposition of the basic electrical quantity, voltage or current, with the signal change caused by the needle movement be suitably separated and then further processed.The characteristic signal shape in the voltage or current signal is evaluated with respect to the time of occurrence. The signals for needle opening are currently detected in the current waveform, and those for needle closing are detected in the voltage waveform. This is illustrated by an example of OPP1. The armature strikes the needle and carries it with it. The change in armature speed induces an eddy current, which is recognizable as an OPP1 signal in the current waveform.

[0006] Thus, for example, the time OPP1 at which the armature strikes the needle and drives it along, whereby the change in armature speed induces an eddy current and the needle movement begins, can be determined by determining a local maximum in the second time derivative of the coil current. The disadvantage here is the occurrence of multiple maxima, which is why an additional plausibility check is required to determine the correct maximum.

[0007] For example, document DE 10 2013 203 130 A1 discloses a method for controlling an injection process of a magnetic injector of an internal combustion engine, wherein the actual opening time of the magnetic injector can be determined from the temporal profile of the induction current flowing through the coil. The induction current represents a unique characteristic feature of the opening of the magnetic injector and a measure of the actual opening time of the magnetic injector.

[0008] Document DE 10 2012 216 611 A1 also discloses a method for operating a solenoid valve. In this method, a first electrical state variable of the solenoid valve is determined in a first time interval before the presumed start of movement of the valve element from the first to the second position, and a second electrical state variable of the solenoid valve is determined in a second time interval before the presumed start of movement of the valve element from the second to the first position. A comparison of the first and second electrical state variables then allows a conclusion to be drawn about the state of the solenoid valve.

[0009] Furthermore, document DE 10 2011 076 363 A1 describes a method for determining the opening behavior of a fuel injector having a coil drive for a motor vehicle's internal combustion engine. This involves applying a test voltage profile to the coil drive so that a magnet armature of the coil drive moves from a closed position to an open position, and measuring the temporal profile of the current flowing through the coil drive. Based on a characteristic feature in the measured temporal profile of the current and a time difference until this feature occurs, the temporal opening behavior of the fuel injector can be determined as a function of the determined time difference.

[0010] The other documents DE 43 22 199 C2, DE 10 2010 041 320 A1, DE 101 50 199 A1, DE 195 44 207 A1 and DE 10 2011 075 935 A1 also disclose various methods for controlling electromagnetically operated actuators and in particular valves, in which armature positions or closing or opening times can be determined by evaluating the time course of the control current or the control voltage or the measured magnetic flux of the respective electromagnet.

[0011] The present invention is based on the object of providing an improved method for determining a point in time at which a fuel injector is in a predetermined state in order to thus enable precise and reliable control of the fuel injector.

[0012] This object is achieved by the subject matter of the independent patent claims. Advantageous embodiments of the present invention are described in the dependent claims.

[0013] According to a first aspect of the invention, a method is described for determining a point in time at which a fuel injector having a solenoid drive for an internal combustion engine of a motor vehicle is in a predetermined opening state. The described method comprises the following: (a) applying a predetermined electrical voltage profile to the solenoid drive, (b) detecting the temporal profile of the current intensity of a current flowing through the coil of the solenoid drive, (c) detecting the temporal profile of the voltage across the coil, (d) determining a function based on the temporal profile of the current intensity and the temporal profile of the voltage, wherein the function represents the interlinked magnetic flux orrepresents a time derivative of the interlinked magnetic flux in the solenoid drive, and (e) determining the time as the time at which the function exhibits a characteristic feature.

[0014] The described method is based on the finding that changes in movement in the mechanical system (in particular the armature and needle) of a fuel injector lead to corresponding changes in the course of the interlinked magnetic flux in the magnetic circuit. By recording the respective temporal course of current and voltage while the fuel injector is controlled by applying a predetermined electrical voltage profile to the solenoid drive and determining a function that represents the interlinked magnetic flux or a temporal derivative (first derivative, second derivative, third derivative, etc.) of the interlinked magnetic flux in the solenoid drive, the time at which the fuel injector is in a predetermined opening state can be determined, namely as the time at which the function exhibits a characteristic feature.

[0015] In this document, "opening state" refers in particular to a state that occurs during an injection process, i.e., during the opening, injection, or closing phase of the fuel injector. Examples include (i) the start of electrical activation or the start of armature movement (also called OPP0), (ii) the onset of mechanical coupling between the armature and nozzle needle or the start of needle movement during opening (also called OPP1), (iii) the needle striking the pole piece or the end of the opening process (also called OPP2), (iv) the initiation of the closing process or the start of needle movement during closing (also called OPP3), (v) the end of the mechanical coupling between needle and armature or the end of needle movement during closing (also called OPP4), and (vi) the end of armature movement during closing (also called OPP5).

[0016] In this document, "predetermined voltage profile" refers specifically to a time-varying voltage used to control the fuel injector. The predetermined voltage profile may, for example, include a boost phase, a hold phase, and a closing phase.

[0017] In this document, "function" refers specifically to a mathematical function that can be used to calculate a corresponding value for a given point in time. The function can be stored, in particular, as a table in memory (for example, by an engine control unit), whereby values not directly derived from the table can be calculated by interpolation.

[0018] In this document, “characteristic feature” means a property of a function that can be identified by mathematical analysis of the corresponding curve, for example by means of numerical methods.

[0019] According to one embodiment of the invention, the characteristic feature is a (local or global) maximum, a (local or global) minimum, a threshold value or an inflection point.

[0020] According to a further embodiment of the invention, determining the function comprises calculating f(t)=u(t)-R*i(t), where u(t) denotes the time course of the voltage across the coil, R denotes the electrical resistance of the coil, and i(t) denotes the time course of the current intensity flowing through the coil.

[0021] This function f(t) corresponds to the time derivative of the concatenated magnetic flux Ψ (Psi), that is f(t)=dΨdt.

[0022] According to a further embodiment of the invention, the function is equal to f(t).

[0023] In other words, in this embodiment, the extremum is determined directly in the time derivative of the concatenated magnetic flux.

[0024] According to a further embodiment of the invention, determining the function comprises calculating the interlinked magnetic flux by integrating f(t) and calculating the time derivative of the interlinked magnetic flux.

[0025] This embodiment is particularly suitable if the interlinked magnetic flux is also used for other purposes or analyses (for example in the engine control unit).

[0026] According to a further embodiment of the invention, the determination of the function and / or the determination of the time are carried out using numerical methods.

[0027] In particular, a modern motor control system can be set up or programmed relatively easily so that the calculations for determining the function and the extremum can be carried out based on the measured voltage and current.

[0028] According to a further embodiment of the invention, the extremum is a maximum, in particular a local or global maximum.

[0029] According to a further embodiment of the invention, the predetermined opening state of the fuel injector is the beginning of an opening phase, the end of the opening phase, the beginning of a closing phase or the end of the closing phase.

[0030] In other words, the method according to the invention can be used to carry out a simple and precise determination of the times corresponding to the opening states OPP1, OPP2, OPP3 and OPP4.

[0031] According to a second aspect of the invention, a method for controlling a fuel injector having a solenoid drive is described. The described method comprises the following: (a) performing a method for determining a time at which the fuel injector is in a predetermined opening state, according to the first aspect or one of the above embodiments, and (b) controlling the fuel injector based on the determined time, wherein, in particular, a duration between the application of a boost voltage for opening the fuel injector and the application of a voltage for closing the fuel injector is reduced or increased if it is determined that the time occurs later or earlier than a reference time.

[0032] With this method, precise control of the exact injection quantity can be achieved in a simple and reliable manner by using the method according to the first aspect. In particular, the actual start (or end) of the hydraulic duration of the injection can be determined and corrected by adjusting the control of the fuel injector so that the desired injection quantity is achieved.

[0033] According to a third aspect of the invention, an engine control for a vehicle is described for using a method according to the first / second aspect and / or one of the above embodiments.

[0034] This engine control makes it possible, by using the method according to the first aspect, to achieve precise control of the exact injection quantities of the individual fuel injectors in a simple and reliable manner.

[0035] According to a fourth aspect of the invention, a computer program is described which, when executed by a processor, is configured to carry out the method according to the first / second aspect and / or one of the above embodiments.

[0036] For the purposes of this document, the mention of such a computer program is synonymous with the term "a program element, a computer program product and / or a computer-readable medium containing instructions for controlling a computer system in order to coordinate the operation of a system or a method in a suitable manner in order to achieve the effects associated with the method according to the invention.

[0037] The computer program can be implemented as computer-readable instruction code in any suitable programming language, such as JAVA, C++, etc. The computer program can be stored on a computer-readable storage medium (CD-ROM, DVD, Blu-ray disk, removable drive, volatile or non-volatile memory, built-in memory / processor, etc.). The instruction code can program a computer or other programmable devices, such as, in particular, a control unit for a motor vehicle engine, to perform the desired functions. Furthermore, the computer program can be provided on a network, such as the Internet, from which it can be downloaded by a user as needed.

[0038] The invention can be implemented both by means of a computer program, ie software, and by means of one or more special electrical circuits, ie in hardware, or in any hybrid form, ie by means of software components and hardware components.

[0039] It should be noted that embodiments of the invention have been described with reference to different subject matter. In particular, some embodiments of the invention are described with method claims, and other embodiments of the invention are described with apparatus claims. However, it will immediately become clear to those skilled in the art upon reading this application that, unless explicitly stated otherwise, in addition to a combination of features belonging to one type of subject matter, any combination of features belonging to different types of subject matter is also possible.

[0040] Further advantages and features of the present invention will become apparent from the following exemplary description of a preferred embodiment. Fig. 1 shows a fuel injector with solenoid drive. Fig. Figure 2 shows plots of current, voltage, injection rate, and armature and needle position as functions of time when controlling a fuel injector. Fig. 3 shows a figure of the second time derivative of the Fig. 1 shown current. Fig. Figure 4 shows a plot of the interlinked magnetic flux as a function of time when controlling a fuel injector. Fig. Figure 5 shows a diagram of the time derivative of the Fig. 4 shown concatenated magnetic flux as a function of time. Fig. 6 shows an enlarged section of the Fig. Figure 5 shown. Fig. 7 shows a flowchart of a method according to the invention.

[0041] It should be noted that the embodiments described below represent only a limited selection of possible embodiments of the invention.

[0042] The Fig. 1 shows a sectional view of a fuel injector 100 with a solenoid drive (solenoid injector). In particular, the injector 100 has a solenoid drive with coil 102 and armature 104. When a voltage pulse is applied to coil 102, the magnetic armature 104 moves toward the wide part of the nozzle needle 106 and then, after overcoming the idle stroke 114 (against the force of spring 110), pushes it upward against the spring forces exerted by springs 110 and 132 until the armature 104 strikes the pole piece 112. After the end of the voltage pulse, the armature 104 and nozzle needle 106 move back down to their starting position on the hydrodisc 108.

[0043] The one in the Fig. The solenoid injector 100 shown in Figure 1 includes several features that are known per se and are of only minor importance to the present invention and therefore will not be described in detail. These features include, in particular, valve body 116, integrated seat guide 118, ball 120, seal 122, housing 124, plastic 126, disc 128, metal filter 130, and calibration spring 132.

[0044] The Fig. Figure 2 shows images of current 210, voltage 220, injection rate 230 and armature and needle position 240 as functions of time when controlling a fuel injector, such as the fuel injector 100 described above. In particular, the Fig. a (predetermined) voltage profile with a boost phase 222 (in which an increased voltage of approximately 65V is used), a hold phase 224 (in which a voltage of approximately 12V is used) and a closing phase 226, 228 (in which first a reversal of the voltage occurs, after which the voltage increases towards 0V). The Fig. shows the corresponding current intensity curve, where the current intensity increases during the boost phase 212 to the peak value (peak current) 213, remains relatively constant in the hold phase 214 and then drops rapidly in the closing phase 216. The Fig. shows the corresponding course of the injection rate, which is greater than zero from the beginning (t≈0.55ms) to the end (t≈1.95ms) of the injection phase 235. Finally, the Fig. the corresponding curves of the armature position or armature stroke 241 and needle position or needle stroke 242. From the Fig. it can be seen that the movement of the needle starts at t≈0.55ms (OPP1) and ends at t≈1.95ms (OPP4).

[0045] The Fig. 3 shows a map of the second time derivative 310 of the Fig. 1. As described in the introduction, the time of the opening state OPP1 (t≈0.55 ms) can be identified as the local maximum 312. However, as can also be seen, the curve has many extremes, which complicates the determination and, in particular, necessitates a plausibility check process that involves additional effort.

[0046] The Fig. 4 shows a diagram of the linked magnetic flux 410 as a function of time at the Fig. 2. The curve 410 falls into three main sections: a first section 412 (boost phase), in which the flow increases steeply, a second section 414 (injection phase), in which the flow increases less steeply, and a third section 416 (closing phase), in which the flow decreases again.

[0047] The Fig. 5 shows a map of the time derivative 510 of the Fig. 4 as a function of time. Curve sections 512, 514 and 516 correspond to curve sections 412, 414 and 416 in the Fig. 4. Furthermore, the point 519 corresponding to the opening state OPP1 (at t≈0.55ms) is marked in the curve 510.

[0048] The Fig. 6 shows an enlarged section 610 of the Fig. 5 shown Fig. . In the section 610, the point 619 corresponding to the opening state OPP1 (at t≈0.55 ms) is again marked and it can be seen that the time derivative 614 of the concatenated magnetic flux here has a local maximum that is not surrounded by many other local maxima and is therefore relatively easy to determine.

[0049] The Fig. Figure 7 shows a flowchart of a method according to the invention for determining a point in time at which a fuel injector having a solenoid drive is in a predetermined opening state. The first predetermined state can be OPP1, for example.

[0050] In step 710, the solenoid drive of fuel injector 100 is subjected to a predetermined electrical voltage profile. The predetermined voltage profile corresponds to a normal control of fuel injector 100 and includes, for example, a boost phase, a hold phase, and a closing phase. For short injections, particularly in conjunction with multiple injections in which the nozzle needle follows a ballistic trajectory, the predetermined voltage profile may only include a boost phase and a closing phase (i.e., no hold phase).

[0051] In step 720, the temporal progression of the current flowing through the coil of the solenoid drive is recorded. Specifically, current values are measured or sampled at short intervals and stored as digital values in memory, for example, in the engine control unit.

[0052] Similarly, in step 730, the time course of the voltage across the coil is recorded. Specifically, voltage values are measured or sampled at short time intervals and stored as digital values in memory, for example, in the engine control unit.

[0053] In step 740, a function is determined based on the time course of the current intensity and the time course of the voltage, wherein the function represents the interlinked magnetic flux or a time derivative of the interlinked magnetic flux in the solenoid drive.

[0054] A function that represents the time derivative of the interlinked magnetic flux is particularly advantageous here. If the engine control unit records the interlinked magnetic flux for other purposes, the function can then be determined by deriving it. Alternatively, the function can be determined as f(t) = u(t) - R*i(t), where u(t) denotes the time course of the voltage across the coil, R denotes the electrical resistance of the coil, and i(t) denotes the time course of the current flowing through the coil.

[0055] The above-mentioned function f(t) is – except for an integration constant, which is irrelevant for the occurrence of a characteristic feature, for example, an extremum – equal to the time derivative of the linked magnetic flux. The measured voltage u(t) consists of an ohmic component (R*i(t)) and an inductive component (u ind(t)). The inductive voltage is calculated from the time derivative of the linked magnetic flux dΨ / dt, where Ψ depends on the current change i(t) and the air gap x(t). u(t)=i(t)R+uind(t)=i(t)R+dΨ(i,x)dt=i(t)R+(dΨ(i,x)dididt+dΨ(i,x)dxdxdt)

[0056] When driving slowly, the “magnetic” component of the induction due to current change is small. uind1=dΨ(i,x)dididt

[0057] The “mechanical part of the induction through the armature movement then describes the strokes (idle stroke and / or working stroke) of the fuel injector. uind2=dΨ(i,x)dxdxdt

[0058] By rearranging and integrating, the linked mechanical flow can be calculated as follows: Ψ=∫(u(t)−i(t)R)dt

[0059] From this it can also be seen that f(t) ≈ dΨ / dt.

[0060] Finally, in step 750, the time point corresponding to the predetermined opening state (e.g., OPP1) is determined as the time point at which the function exhibits a characteristic feature, in particular an extremum. This feature can be determined, in particular, using numerical methods known per se.

[0061] With the method according to the invention, the point in time at which a fuel injector is in a predetermined opening state (e.g., OPP1) can be determined precisely and easily (based on current and voltage measurements). The determined point in time can be used, for example, by the engine control unit, in particular to adjust the voltage profile used to control the fuel injector in order to achieve or approach a predetermined injection quantity. List of reference symbols 100 fuel injector 102 coil 104 anchors 106 jet needle 108 Hydro-Disc 110 spring 112 Pole piece 114 idle stroke 116 valve body 118 Integrated seat guide 120 balls 122 Seal 124 housings 126 plastic 128 disc 130 metal filters 132 Calibration spring 210 Illustration of current intensity 212 Boost phase 213 Peak current 214 Holding phase 216 Closing phase 220 Illustration of voltage 222 Boost phase 224 Holding phase 226 Closing phase 228 Closing phase 230 Illustration of injection rate 235 Injection phase 240 Illustration of anchor and needle position 241 Anchor position 242 Needle position 310 Illustration of second derivative of current 312 Opening state OPP1 410 Illustration of linked magnetic flux 412 Boost phase 414 Holding phase 416 Closing phase 510 Illustration of the time derivative of the concatenated magnetic flux 512 Boost phase 514 Holding phase 516 Closing phase 519 Opening state OPP1 610 Illustration of a section of the time derivative of the concatenated magnetic flux 614 Holding phase 619 Opening state OPP1 710 Process step 720 process step 730 process step 740 process step 750 process steps

Claims

[1] Method for determining a time at which a fuel injector having a solenoid drive for an internal combustion engine of a motor vehicle is in a predetermined opening state, the method comprising Applying (710) a predetermined electrical voltage profile to the solenoid drive, detecting (720) the time course of the current intensity of a current flowing through the coil of the solenoid drive, Detecting (730) the time course of the voltage across the coil, Determining (740) a function based on the time course of the current intensity and the time course of the voltage, wherein the function represents the linked magnetic flux or a time derivative of the linked magnetic flux in the solenoid drive, and Determining (750) the time as the time at which the function has a characteristic feature. [2] Method according to the preceding claim, wherein the characteristic feature is a maximum, a minimum, a threshold or an inflection point. [3] Method according to one of the preceding claims, wherein determining the function comprises calculating f(t)=u(t)-R*i(t), where u(t) denotes the time course of the voltage across the coil, R denotes the electrical resistance of the coil and i(t) denotes the time course of the current intensity of the current flowing through the coil. [4] Method according to the preceding claim, wherein the function is equal to f(t). [5] The method of claim 3, wherein determining the function comprises calculating the interlinked magnetic flux by integrating f(t) and calculating the time derivative of the interlinked magnetic flux. [6] Method according to one of the preceding claims, wherein the determination of the function and / or the determination of the time are carried out using numerical methods. [7] Method according to one of the preceding claims, wherein the predetermined opening state of the fuel injector is the beginning of an opening phase, the end of the opening phase, the beginning of a closing phase or the end of the closing phase. [8] Method for controlling a fuel injector having a solenoid drive, the method comprising Carrying out a method for determining a time at which the fuel injector is in a predetermined opening state according to one of the preceding claims and Controlling the fuel injector based on the determined time, wherein in particular a duration between the application of a boost voltage for opening the fuel injector and the application of a voltage for closing the fuel injector is reduced or increased if it is determined that the time occurs later or earlier than a reference time. [9] Engine control for a vehicle, arranged to use a method according to any one of the preceding claims. [10] A computer program which, when executed by a processor, is arranged to carry out the method according to any one of claims 1 to 8.

Images