Method for controlling a fuel injection solenoid valve and corresponding engine control unit

Abstract

Method for controlling a solenoid valve having a coil (3) and an armature (9) displaceable by magnetic force, by means of which a closure element (11) is displaceable in order to inject fuel (19) into a combustion chamber (23), the method comprising: Applying a voltage (84) according to a first voltage curve to the coil (3) in order to generate a first electrical current (81) through the coil (3); Determining a first profile (31, 37) as a function of a first magnetic flux (Ψ) and the first current (i); Detecting, in the first course, a first characteristic of at least a first displacement start (I) at which the armature (9) begins to displace the closure element (11), Generating a second voltage curve different from the first voltage curve and applying the coil according to the second voltage curve, such that in a second curve, depending on a second magnetic flux and a second current, a second characteristic of a second displacement start (I) is more similar to a reference characteristic than the first characteristic, wherein the first characteristic comprises a slope of the first curve, determined by the derivative of the first magnetic flux with respect to the first current, and the second characteristic comprises a slope of the second curve, determined by the derivative of the second magnetic flux with respect to the second current, and wherein the reference characteristic comprises at least one reference slope.

Description

[0001] The present invention relates to a method and a device for controlling a solenoid valve for injecting fuel into a combustion chamber. In particular, the present invention relates to an engine control unit configured to control a fuel injection solenoid valve.

[0002] 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. Due to a mechanical coupling (e.g. a mechanical contact), after overcoming the idle stroke, the nozzle needle or the closing element (during the working stroke or needle stroke) also moves 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 valve, the excitation voltage applied to the coil is switched off and the coil is short-circuited so that the magnetic force dissipates.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.

[0004] The time at which the needle movement begins when the solenoid valve opens can depend on the length of the idle stroke. The time at which the needle or armature hits the pole piece depends on the length of the needle stroke or working stroke. The injector-specific temporal variations in the start of the needle movement (opening) and the end of the needle movement (closing) can result in different injection quantities with identical electrical control.

[0005] After the armature has overcome the idle stroke required to open the solenoid valve (assuming an idle stroke is present in the solenoid valve in question), the armature strikes the pole piece, which prevents further movement or displacement of the armature in the direction of opening the solenoid valve. At this stop, the armature can be elastically repelled, and after the armature has been repelled a certain distance, it can again strike the pole piece. In this way, the armature can perform a bouncing movement in which it is repelled at least once by the pole piece, accelerated in a direction to close the solenoid valve, and then, due to the remaining magnetic force, accelerated and displaced in the direction to open the solenoid valve. The bouncing process can comprise one or more impact states of the armature against the pole piece.

[0006] The bouncing or bouncing movement can vary in different injectors or solenoid valves, e.g., with regard to different damping due to mechanical deviations (hydraulic gap), different materials, different elastic properties, different masses of the moving parts, especially the armature, etc. Thus, different solenoid valves or injectors can result in different flow characteristics if the injector is closed again during the bouncing process. A closing process can depend in particular on whether the armature moves toward opening the valve or toward closing it at the start of an intended closing process.

[0007] Furthermore, injector control (particularly the control of the solenoid valve to open the solenoid valve) can be difficult or inaccurate in this bounce range or during the bounce movement, since a clear dependence on the control duration (e.g., duration of the boost voltage and / or duration of a holding voltage interval) and the injection quantity may not always be present. For example, the injection quantity may decrease despite increasing control duration (particularly increasing duration of the boost voltage and / or increasing duration of the holding voltage during a voltage profile).

[0008] Thus, in conventional injection systems that use a solenoid valve, inaccuracies can arise with regard to the desired injection quantity of fuel and also with regard to the desired timing of the fuel injection.

[0009] In conventional processes, injection times exhibiting pronounced bounce behavior are avoided when controlling the solenoid valve. This allows the areas with the negative effects of bounce behavior to be excluded from the fuel flow map. However, this significantly limits the control, which can have negative effects on the operation of the combustion engine.

[0010] It is therefore an object of the present invention to provide a method and a device, in particular an engine control unit, which allows an injection process to be improved compared to the prior art, particularly with regard to an injection quantity and a timing of the injection. In particular, it is an object of the present invention to reduce inaccuracies or unreliabilities due to bouncing in a solenoid valve.

[0011] US Pat. No. 6,128,175 A discloses a method for controlling the speed of an armature of a fuel injector as the armature moves from a first position to a second position. A coil, a stator core, and an armature of the fuel injector form a magnetic circuit. The coil generates a magnetic force that causes the armature to move toward and impact the stator core. The method includes energizing the coil to allow the armature to move toward the stator core. A rate of change of the magnetic flux of the magnetic circuit is determined. Feedback control of the determined rate of change of the magnetic flux is used to regulate a rate of the magnetic flux by controlling the coil current. This allows the speed of the armature as it impacts the stator core to be controlled.

[0012] From DE 10 2004 021 366 A1 a method for assessing the opening and closing behavior of a solenoid injection valve for an internal combustion engine is known.

[0013] A high-pressure pump is known from DE 10 2010 064 048 A1. The high-pressure pump comprises a hydraulic valve having a closing body that can be actuated by an electromagnetic actuator to close the valve. The actuator is activated with a predetermined control signal at a predetermined activation time to close the valve. Furthermore, a profile of an actuator voltage is recorded during a predetermined diagnostic phase, which occurs after the predetermined activation period and includes at least one expected opening time of the valve. A first characteristic variable is determined that represents a first time or a first crankshaft angle at which the recorded actuator voltage has a local minimum in the diagnostic phase after a predetermined closing period of the valve.Furthermore, the determined first characteristic value is compared with a predefined reference characteristic value that is representative of a reference time or a reference crankshaft angle. A predefined control signal is signaled depending on the comparison.

[0014] DE 10 2005 042 110 A1 discloses a method for shortening the delay times when closing an electromagnetic actuator. In this method, the reduction of the magnetic flux is accelerated by applying a reversing current. The duration of the reversing pulse is selected to minimize the magnetic force.

[0015] This object is achieved by the subject matter of the independent claims. The dependent claims specify particular embodiments of the present invention.

[0016] According to a first aspect of the present invention, a method is provided for controlling a solenoid valve having a coil and an armature displaceable by magnetic force, by means of which a closure element is displaceable in order to inject fuel into a combustion chamber.The method comprises applying a voltage to the coil according to a first voltage curve in order to generate a first electric current through the coil, determining a first curve as a function of a first magnetic flux and the first current, detecting, in the first curve, a first characteristic of at least a first displacement start at which the armature begins to displace the closure element, generating a second voltage curve different from the first voltage curve and applying the coil according to the second voltage curve such that in a second curve as a function of a second magnetic flux and a second current, a second characteristic of a second displacement start is more similar to a reference characteristic than the first characteristic.The first characteristic comprises a gradient of the first curve, determined by the derivative of the first magnetic flux with respect to the first current, and the second characteristic comprises a gradient of the second curve, determined by the derivative of the second magnetic flux with respect to the second current. The reference characteristic comprises at least one reference gradient.

[0017] The method can be carried out by a special control unit in a workshop or a manufacturing factory, or in particular by an engine control unit that is installed and used in a vehicle for normal driving. The closure element can be designed, for example, as a needle, in particular a nozzle needle, which carries a closure ball at one end. This ball rests in a conical seat when the solenoid valve is closed and is displaced from the seat when it is open, allowing the fuel to flow into the combustion chamber through an opening in the seat.

[0018] The first voltage curve and the second voltage curve can each comprise a boost phase, for example, in which the voltage has a relatively high value, for example between 60V and 70V, in particular around 65V. The voltage curve within the boost phase can, for example, essentially have a square wave signal or a sawtooth signal. After the boost phase, both the first voltage curve and the second voltage curve can be followed by a hold phase in which the voltage is considerably lower than in the boost phase, for example between 6V and 14V. The hold phase can be longer in time (for example between four times as long and 10 times as long) than the boost phase. The hold phase can, for example, last from 1 millisecond to 2 milliseconds. The hold phase can in turn be divided into several phases, for which different average current levels are specified. When these current levels are reached, the voltage is switched on or off.switched off, so that the current oscillates around this current level. In the final phase, the injector is disconnected from the power supply and short-circuited.

[0019] The first voltage profile and the second voltage profile can differ in the magnitude of the boost phase, the duration of the boost phase, and the profile of the boost phase (e.g., the voltage profile during the boost phase, e.g., an alternating square wave signal, a sawtooth signal, or the like). Furthermore, the first and second voltage profiles can differ with respect to the voltage during the hold phase and also with respect to the duration of the hold phase.

[0020] Applying the voltage according to the first voltage curve or the second voltage curve generates a corresponding current curve in the coil. This corresponding current curve leads to a magnetic field curve, which, in addition to geometric influences, influences the relative positioning of the armature, locking element, driver, and pole piece.

[0021] The first profile as a function of a first magnetic flux and the first current can depend directly on the first magnetic flux and the first current or on quantities which are derived from the first magnetic flux and the first current, e.g. are functions of the first magnetic flux or the first current. The first profile can then be analyzed or evaluated in order to characterize the first start of displacement. The first profile can, as a function of the first magnetic flux and the first current, can, for example, contain a section in which the armature is already resting on the closure element or a driver connected to the closure element and making contact with it without displacing the driver or the closure element.Therefore, no movement is observed in this section, as an increasing magnetic force must first build up to at least equal the force counteracted by the fuel pressure. At the beginning of the displacement, a force equilibrium is just reached, where the force due to the magnetic flux is equal to the force due to the fuel pressure.

[0022] Characterizing at least this first displacement start can allow conclusions to be drawn about the fuel pressure. Furthermore, an expected bounce behavior can be predicted from this, and the second voltage curve can be determined in such a way that the expected bounce is reduced. A second characteristic of the second displacement start can be indicative of a reduced bounce behavior or a reduced bounce amplitude. This second characteristic is more similar to a reference characteristic than the first characteristic, which reduces bounce.

[0023] To determine the respective characteristics, not only a respective displacement start can be used, but one or more sections or the entirety of the respective course, which is determined as a function of the respective magnetic flux and the respective current, in particular represented by a curve in a coordinate system which contains the current through the coil and the magnetic flux.

[0024] The solenoid valve can therefore be controlled before the solenoid valve actually opens, in order to intervene in the control as early as possible in order to be able to inject a defined amount of fuel into the combustion chamber when it opens.

[0025] According to the method according to the invention, an improvement in the bounce behavior of magnetic injectors can be achieved by evaluating the magnetic flux and current or voltage adaptation.

[0026] The first curve or the second curve can be represented by a first curve or a second curve in a coordinate system in which the current is plotted along one axis (e.g., the X-axis) and the magnetic flux is plotted along another axis (e.g., the Y-axis). The magnetic flux can be calculated, for example, from the measured voltage and the measured current, taking into account the ohmic resistance of the coil. This allows the first curve or the second curve to be easily determined and, in particular, visualized, and thus easily evaluated.

[0027] The first characteristic or the second characteristic can, for example, comprise a gradient (dΨ / di) and / or a position (i.e. position of current or magnitude of current and magnitude of the magnetic flux) on the respective curve, in particular at least at the respective start of the displacement, furthermore in particular along at least a section of an opening movement of the closure element between the start of the displacement and a contact state in which the armature abuts a pole shoe to end the opening movement (for the first time). The reference characteristic can thereby comprise at least a reference gradient and / or a reference position. The respective characteristics can thus be determined in a simple manner, for example by mathematical curve analysis. The respective contact state can thereby represent the end of the opening movement. If bouncing should occur during actuation according to the first voltage profile orIf the expected contact state is not met, the first contact state can be considered the first contact of the armature against the pole piece. It may be advantageous to determine the expected bouncing solely based on the characteristic at the beginning of the displacement, thus being able to intervene before the solenoid valve opens to shape the second voltage curve in such a way that the expected bouncing is reduced.

[0028] The respective displacement start point can be identified as a point or a region on the Ψ-i curve (magnetic flux plotted against current) where the gradient of the respective curve changes. Other ways of identifying the respective displacement start point are possible.

[0029] The respective contact state can be identified as a point or region (on the Ψ-i curve) where the slope of the respective curve changes. Other methods for identifying the contact state are possible.

[0030] This allows both the displacement start and the contact state to be reliably located.

[0031] The coil can be energized according to the second voltage curve before the first contact state, i.e. also before any bouncing. In particular, the second voltage curve can have a different, in particular extended, shortened or interrupted duration of a boost phase than the first voltage curve. The duration of the boost phase can be adjusted in such a way that bouncing, which would occur if the voltage were continued according to the first voltage curve, is reduced. In this case, for example, the first curve between the start of the displacement and the contact state can be evaluated in order to then define the second voltage curve. For example, the start of the displacement, in particular the first start of the displacement, can be detected and a predetermined control / pre-control can be carried out from or at the first start of the displacement (e.g.Current value at the start of the shift plus a defined current difference or plus an extension of the boost phase). Other modifications or adjustments of the second voltage curve are possible.

[0032] The coil can be energized according to the second voltage curve after the first contact state, in particular after the first impact but before any bouncing movement. In this case, the second voltage curve, in particular, can have a different, in particular longer or shorter, duration of a boost phase than the first voltage curve, or it can have an interrupted boost phase characterized by several partial boost phases, each interrupted by a phase of reduced voltage.

[0033] For example, the first contact point (in particular the first impact of the armature on the pole piece) can be detected while the first voltage curve is applied to the coil. After the first contact point is detected, a predetermined control / pre-control can be carried out at the first contact point (e.g. current value at the first contact point plus a defined current difference or plus an extension of the boost phase or interruption of the boost phase with subsequent continuation). Combinations of controls after the start of the displacement has been detected, between the start of the displacement and the first contact point, and an entire section between the start of the displacement and the first contact point can be used to define the second voltage curve. This can reduce bouncing, which could occur when the voltage is applied according to the first voltage curve.

[0034] Furthermore, the respective characteristic can be determined depending on at least one section of the respective curve beyond the contact state (in particular beyond a respective first impact of the armature against the pole piece), wherein the second voltage curve is configured such that the section has fewer alternating gradients. This allows a bouncing process to be at least shortened by controlling the bouncing process after it begins.

[0035] To locate or define the second voltage curve, a simulation or testing of the operation of the solenoid valve can be performed. In particular, training data can be recorded based on various voltage curves, and the voltage curves or the test voltage curves can be characterized with regard to the occurrence of bouncing. In particular, an analysis of sections of the various curves thus obtained can determine a relationship between a characteristic of certain sections of the curve and a (later occurring) bouncing. In particular, a prediction of possible bouncing can thus be made based on an analysis of certain sections of the curve before the bouncing.

[0036] Furthermore, the method may comprise providing at least one reference data set, wherein the reference data set may comprise a reference curve of current and magnetic flux with sufficiently low bouncing of the armature against the pole piece. The second voltage curve may then be configured such that a curve obtained based on the second voltage curve is relatively similar to or close to the reference curve.

[0037] Of course, the voltage according to the first voltage curve does not have to be applied for the entire time interval defined by the first voltage curve. Instead, the application of the voltage according to the first voltage curve can be interrupted at the respective point (e.g., at the first start of displacement, between the first start of displacement and the first contact state) or even beforehand, and the voltage can be continued according to the second voltage curve, starting at the point at which the first voltage curve was interrupted. In other embodiments, the first voltage curve is passed through completely, and for a further opening process of the valve, a voltage according to the second voltage curve is applied to the coil.

[0038] According to a second aspect of the present invention, a device, in particular an engine control unit, is provided for controlling a solenoid valve having a coil and an armature displaceable by magnetic force, by means of which a closure element is displaceable in order to inject fuel into a combustion chamber.The device comprises a driver for applying a voltage to the coil according to a first voltage curve in order to generate a first electric current through the coil, and a determination module which is designed to determine a first curve as a function of a first magnetic flux and the first current and to detect, in the first curve, a first characteristic of at least a first displacement start at which the armature begins to displace the closure element, wherein the driver is further designed to generate a second voltage curve which is different from the first voltage curve and to apply a voltage to the coil according to the second voltage curve such that in a second curve as a function of a second magnetic flux and a second current, a second characteristic of a second displacement start is more similar to a reference characteristic than the first characteristic.The first characteristic comprises a gradient of the first curve, determined by the derivative of the first magnetic flux with respect to the first current, and the second characteristic comprises a gradient of the second curve, determined by the derivative of the second magnetic flux with respect to the second current. The reference characteristic comprises at least one reference gradient.

[0039] The determination module can comprise, for example, an arithmetic / logic unit, an electronic memory, and a communication connection to the driver. The device can be configured to carry out a method according to embodiments of the present invention. The method can be carried out during normal driving operation. The magnetic flux can pass through the armature and partially through the pole piece, which is fixed relative to the coil, and also through parts of the closure element or at least parts of a driver, which is fixedly connected to the closure element.

[0040] According to embodiments of the present invention, a method is proposed in which the injector movement (in particular movement of the closure element) is detected with the aid of the Ψ-i curve and the control is modified (from the first voltage profile to the second voltage profile) in such a way that the bouncing behavior is reduced. In this case, the needle movement, e.g. state I (start of displacement) and / or state II (contact state), can be determined in the Ψ-i curve and the associated control can be optimized with regard to bouncing reduction, e.g. by modifying the peak current level (or boost voltage level) or interrupting the control voltage (e.g. in the boost phase). For example, the entire needle movement between state I (start of displacement) and the contact state orState II can be detected, and the control can be adjusted so that the gradients dΨ / di are the same for different injectors during the movement (adaptation to the setpoint or reference curve). If state I (start of displacement) is included in the detection, then the needle movement can be brought to a bounce-minimized path immediately after the start of the movement by suitable control, i.e., control intervention can take place before the bounce process.

[0041] In order to be able to measure the Ψ-i curves even with standard control of the solenoid valve, a design of an injector (or solenoid valve, in particular an armature) is proposed in which no or reduced eddy currents occur. In such an injector with reduced eddy currents, the curve progressions during the stroke movements are more pronounced, so that identification of state I (start of displacement) and state II (contact state) can be simplified. In this case, the materials and / or geometries can be adapted. In particular, a slotted armature or an armature constructed from ferromagnetic layers that are electrically insulated from one another can be used. Embodiments of the present invention can determine the armature stop on the pole piece and make a corresponding modification of the control profile to reduce / avoid bounce.It is advantageous to use an injector with no or low eddy current so that the Ψ-i curves can be determined under standard control, i.e. especially during normal driving operation.

[0042] Embodiments of the present invention provide individual injector control to prevent bounce and associated deficiencies in fuel flow characteristics. This enables the adjustment of fuel flow characteristics for rail injectors.

[0043] The invention will now be explained with reference to the accompanying drawings. The invention is not limited to the illustrated or described embodiments. Fig. 1 illustrates, in a schematic sectional view, a solenoid valve that can be controlled according to a method according to embodiments of the present invention; Fig. 2 illustrates graphs of reference data or state trajectories or measurement data of a solenoid valve to be controlled according to embodiments of the present invention; Fig. 3 illustrates graphs of reference data or state trajectories or measurement data of a solenoid valve to be controlled according to embodiments of the present invention; Fig. 4 illustrates flow characteristics for injectors with and without bouncing according to the state of the art; Fig. Figure 5 illustrates graphs of state trajectories obtained by different drive voltage profiles; Fig. 6 illustrates graphs illustrating a solenoid valve control or injector control; and Fig. 7A, B, C, D show graphs according to embodiments of the invention.

[0044] The Fig. The solenoid valve 1, illustrated in a schematic sectional view in Figure 1, has a coil 3 to which a voltage can be applied, so that a current flows through the coil 3 to generate a magnetic field. The magnetic field essentially points in a longitudinal direction 5 of a guide cylinder 7. The magnetic field acts on a ferromagnetic armature 9, which is displaceable within the guide cylinder 7. By displacing the armature 9, a nozzle needle 11 or a closure element of the solenoid valve 1 can be displaced in the longitudinal direction 5, in particular by contacting the armature 9 with an annular driver 13, which is firmly connected to the closure element 11.

[0045] In the Fig. In the open state illustrated in Figure 1, a closure ball 15 is retracted from a conical seat 17, allowing fuel 19 to flow through an opening 21 in the seat into a combustion chamber 23 for combustion. In the fully open state, the armature 9 rests against a pole piece 27 and thus cannot be displaced further upward.

[0046] In a Fig. 1, the armature 9 is displaced downwards by a return spring 25 when there is no current flow through the coil 3, so that the driver 13 together with the closure element 11 is also displaced downwards in such a way that the closure ball 15 lies sealingly against the conical seat 17, so that fuel 19 cannot get into the combustion chamber 23. In this downwardly displaced state of the armature 9, the driver 13 or likewise the armature 9 has covered at least one working stroke 12 (during which the armature 9 and the driver 13 are in contact) and optionally also an additional idle stroke 10, in which a gap exists between the armature 9 and the driver 13.

[0047] Fig. 1 further shows a device 2 for controlling the solenoid valve 1 according to an embodiment of the present invention. For this purpose, the device 2 has a driver 4, which is designed via a measuring and control line 8 to apply a voltage to the coil 3 according to various voltage curves in order to generate a respective electric current through the coil 3. For this purpose, the device 2 has a determination module 6, which is designed to determine curves or curves depending on a respective magnetic flux and a current flowing through the coil 3, such as the Ψ-i curves, which are shown, for example, in the Fig. 2, Fig. 3 and Fig. 5. Furthermore, the determination module 6 is configured to detect, in the first profile, a first characteristic of at least one first displacement start at which the armature begins to displace the closure element. The determination module 6 is further configured, together with the driver 4, to modify the original or first voltage profile or to determine a second voltage profile, such that a characteristic of the respective displacement start is more similar to a reference characteristic than the original or first characteristic.

[0048] In particular, the device 2 is designed to carry out a method for controlling a solenoid valve according to an embodiment of the present invention.

[0049] At the end of the opening process, the armature 9 bounces against the pole piece 27 upon impact. This allows the armature to be elastically repelled, and the impact and repelling can occur repeatedly, so that a bouncing motion can be performed by the armature. This bouncing motion leads to uncertainties and inaccuracies in the injection quantity of fuel 19 into the combustion chamber 23.

[0050] Embodiments of the present invention are aimed at reducing bouncing by making control interventions in a voltage curve or in a voltage profile according to which the coil 3 is controlled. In this case, the interlinked magnetic flux Ψ is measured and analyzed. For this purpose, the interlinked magnetic flux Ψ can be calculated from the current flowing through the coil 3, the voltage applied to the coil 3, and the ohmic resistance of the coil 3. The measured voltage u(t) consists of an ohmic component (i(t) * R) and an inductive component (u int (t)). The inductive voltage is calculated from the time derivative of the interlinked magnetic flux, where Ψ depends on the current change i(t) and the air gap x(t). u(t)=i(t)R+uind=i(t)R+dΨ(i, x)dt=i(t)R+(dΨ(i, x)dididt+dΨ(i, x)dxdxdt)

[0051] When driving slowly, the “magnetic” component of the induction due to current change is small. uind1=dΨ(i, x)dididt

[0052] The “mechanical part of the induction through the armature movement then describes the strokes (idle stroke and / or working stroke) of the solenoid valve. uind2=dΨ(i, x)dxdxdt

[0053] By rearranging and integrating, the linked mechanical flow can be calculated as follows: Ψ=∫(u(t)−i(t)R)dt

[0054] Fig. 2 illustrates a graph 29 with a state trajectory 31 during a pull-in (i.e., during an opening process) or a trajectory 33 during a release (i.e., during a closing process) of the solenoid valve 1 (here for the case with idle stroke). The current i flowing through the coil 3 is plotted on an abscissa 30, and the magnetic flux Ψ calculated according to the above equation is plotted on the ordinate 32. The trajectory 31 can, for example, be determined during a method for controlling the solenoid valve, for example by measuring current, voltage, and calculating the magnetic flux as explained above. From a comparison with Fig. 2 reference data or reference trajectories (not illustrated) can be used to determine a suitable voltage curve to reduce bounce. Points I', II', I, II are Fig. Two characteristic states during the opening process are described. Between points I' and II', the idle stroke ranges from 134 µm to 90 µm, i.e., the pull of armature 9 during the idle stroke. Between points I (start of displacement) and II (contact state), the working stroke ranges from 90 µm to 0 µm, i.e., the pull of armature 9 during the working stroke. In the range II'-I, the armature rests against the driver 13.

[0055] According to embodiments of the present invention, for a solenoid valve without idle stroke (see Fig. 3 below) or with idle stroke ( Fig. 2) The area of ​​trajectory 31 at point I and / or up to point II is evaluated. In the area I'-II', the gradient of trajectory 31 changes compared to the sections before or after it. Furthermore, in the section between points I and II, the gradient changes from a positive value to a negative value.

[0056] In Fig. 2, for example, for a solenoid valve with idle stroke in a region 34 after the second state II, at which the armature 9 first strikes the pole piece 27, a wavy line can be seen, which may indicate bouncing. According to embodiments of the present invention, different voltages (e.g., according to the voltages described below with reference to Fig. 6) and the Ψ-I curves can be determined and evaluated. Voltage curves which do not bounce, i.e. in particular do not have any wavy lines in the area 34, can be marked as advantageous and can be used to actually control the solenoid valve. Other voltage curves which give rise to serpentine lines or wavy lines or disturbances in the area 34 can be excluded from serving as control voltage curves for the solenoid valve 1. From a set of training data, predictions can be made based on a specific voltage curve (e.g. boost voltage level, boost voltage duration, hold voltage level, hold voltage duration), which could predict any bouncing that may occur.

[0057] Fig. Figure 3 illustrates a graph 35 illustrating trajectories 37 and 39 during a pull-in and a release of the armature 9 of the solenoid valve 1, respectively, in the case where the solenoid valve 1 has no idle stroke. Since the idle stroke in the Fig. 3 illustrated trajectory 37 is missing, the characteristic points I' and II' are missing, which are shown in Fig. 2. Between points I and II, the working stroke ranges from 50 µm to 0 µm. At point I, trajectory 37 exhibits a kink where a positive gradient reverses into a negative gradient.

[0058] Fig. Figure 4 illustrates a graph where the injection time TI in milliseconds is plotted on the abscissa 60 and the injection quantity MF in milligrams is plotted on the ordinate 62. The injection time indicates the duration for which the injector is open. Curve 63 illustrates the quantity characteristic for a solenoid valve exhibiting bounce, and curve 65 illustrates the case of an injector exhibiting no or only very slight bounce.

[0059] For the injection valve which exhibits only very slight bouncing (curve 65), there is an almost linear relationship between the injection time and the injection quantity, at least for injection times which are greater than a threshold value (approximately 0.3 ms), which is identified by reference numeral 67. For the solenoid valve which exhibits bouncing (curve 63), there is a strong deviation from linear behavior in a range 69 of short injection times, i.e. from a linear relationship between the injection time and the injection quantity. According to conventional methods, an injection time in range 69 is avoided for such solenoid valves. This would make it impossible in the prior art to implement or execute relatively short injection times, in particular in a range between approximately 0.3 ms and 0.4 ms, since a monotonic gradient is not present.

[0060] Embodiments of the present invention determine the magnetic flux at an early stage during an opening movement or during an opening process of the solenoid valve and intervene in an early controlling manner by adjusting the voltage applied to the coil in such a way that any bouncing that is likely to occur is reduced.

[0061] The characteristics of the Ψ-I curve at different control voltages (3V ... 18V) are shown in the Fig. 5 by trajectories 47 (excitation voltage 18V), 49 (excitation voltage 6V), 51 (excitation voltage 12V) and 53 (excitation voltage 3V). Fig. As can be seen in Figure 5, it is increasingly difficult to reliably detect states I and II at higher voltages, since only small slope changes occur. For example, at an excitation voltage of 18V, it may be difficult to reliably detect state I. Therefore, a measurement of reference curves or a measurement to determine a stroke can be carried out at relatively low excitation voltages, e.g., between 3V and 12V. Fig. 5 illustrated curves 47, 49, 51 and 53 can represent measured data or reference data.

[0062] Fig. 6 illustrates three graphs 70, 72 and 74 illustrating control of a solenoid valve according to embodiments of the present invention.

[0063] The time in microseconds is plotted on the abscissas 76. The magnitude of the voltage applied to coil 3 is plotted on the ordinate 78 of graph 70, the magnitude of the current through coil 3 is plotted on the ordinate 80 of graph 72, and the injection rate (i.e., injection quantity per unit of time) of the fuel is plotted on the ordinate 82 of graph 74 when the solenoid valve is controlled according to the voltage profile of graph 70.

[0064] The voltage curve 84 in the graph 70 of the Fig. 6 comprises a boost phase 85, a hold phase 87, and a ramp-down phase 91. During the boost phase 85, a boost voltage of approximately 50V or up to 65V is applied to coil 3 to open valve 1. The boost voltage is maintained for a period of between 300 µs and 600 µs. In particular, the boost voltage is maintained until a defined current value or a maximum time duration is reached. During this boost phase 85, the armature or needle movement occurs, and thus the stroke signal in the Ψ-I curve is weak. This can be particularly the case when a conventional armature is used, which generates very high eddy currents at relatively high boost voltages.

[0065] In the conventional method, needle bounce can only be detected unclearly and adapting the electrical control to the needle movement to reduce bounce can be difficult.

[0066] Graph 72 shows, with a curve 81, the current curve resulting from the voltage profile 84 in the coil. At the beginning of the boost phase 85, the current 81 rises sharply and reaches a maximum at the end of the boost phase. During the hold phase 87, the current decreases; however, the valve is held open during this phase and is essentially controlled to a zero value after completion of the shut-off phase 91. Beyond phase 91, the solenoid valve is closed.

[0067] Curve 83 of graph 74 shows the injection rate as a function of time. After completion of the boost phase 85, the injection rate has increased to a certain value, which is maintained except for minor fluctuations during the hold phase 87. The point in time marked with reference numeral 90 represents the point in time at which the injector is fully opened.

[0068] The injection rate curve 83 can have a high degree of agreement or correlation with the needle movement. Despite the injector being fully opened (armature touching the pole piece), the control voltage is maintained and thus the accelerating magnetic force continues to increase, which conventionally leads to increased bouncing. The bouncing processes between the individual injectors can vary, since the injectors open at different times and thus the force curves after full opening can be different. Furthermore, the damping properties of the injectors can vary due to the respective geometry of the damping gap. Embodiments of the present invention allow for control intervention by modifying the voltage curves, such as the voltage curve 84, which is shown in graph 70 of the Fig. 6 is illustrated. With the aid of a recorded Ψ-I curve, according to one embodiment of the present invention, the injector movement is detected (in particular also online during operation of a vehicle) and the control is modified such that the bouncing behavior is reduced. For this purpose, for example, the needle movement (state I and / or state II) can be determined in the Ψ-I curve and the associated control can be optimized with regard to bouncing, e.g. by modifying the peak current level (of current 81) or interrupting the control voltage (voltage 84, e.g. during the boost phase 85, during the hold phase 87 or a combination of the two).

[0069] For example, the entire needle movement between the first state I and the second state II can be detected (see e.g. Fig. 2 or Fig. 3) and the control can be adjusted so that the gradients dΨ / di are the same for different injectors during the movement (adaptation to the setpoint or reference curve). If the first state I is included in the detection, the needle movement can be brought onto a bounce-minimized path by suitable control after the start of the movement, i.e. control intervention can already take place before the bounce process. Such control intervention before the bounce can, for example, comprise detecting the first state I and executing a predetermined control / pre-control before or at the first state I (e.g. the current value in the first state I can be adjusted or set plus a defined current difference or plus an extension of the boost phase).

[0070] Alternatively or in combination, a control intervention can also take place after the armature has struck the pole shoe, e.g. by detecting the second state II and executing a predetermined control / pre-control in the second state II (e.g. the current value in the second state plus a defined current difference or plus an extension of the boost phase or interruption of the boost phase with subsequent continuation).

[0071] The Fig. 7A, B, C, D show graphs illustrating the anchor behavior for different cases when controlling according to embodiments of the invention: without bouncing (solid, curves marked with 'a'), with bouncing (dotted, curves marked with 'b') and with soft landing (dashed, curves marked with 'c').

[0072] The bouncing is shown in the PSI-I curve 92a, 92b, or 92c in Fig. 7A. To minimize the bounce, the duration of the boost phase 85 of the control profile 84a, 84b, 84c is extended for the following activations and thus the force on the armature during the stop is increased (see Fig. 7D).

[0073] Another solution is a so-called 'soft landing'. Here, the armature is decelerated before reaching the pole piece by shortening the duration of the boost phase, thus impacting with reduced momentum, which in turn reduces or even prevents bouncing.

[0074] The armature stroke is in Fig. 7B versus time for the different cases as curves 94a, 94b, 94c.

[0075] The current is in Fig. 7C versus time for the different cases as curves 96a, 96b, 96c.

[0076] According to a particular embodiment of the invention, the use of an injector with no or reduced eddy currents is proposed. In such a case, it may be possible to perform the Ψ-I curves even with a standard control (e.g., with a 65V boost voltage).

Claims

[1] Method for controlling a solenoid valve having a coil (3) and an armature (9) displaceable by magnetic force, by means of which a closure element (11) is displaceable in order to inject fuel (19) into a combustion chamber (23), the method comprising: Applying a voltage (84) according to a first voltage curve to the coil (3) in order to generate a first electrical current (81) through the coil (3); Determining a first profile (31, 37) as a function of a first magnetic flux (Ψ) and the first current (i); Detecting, in the first course, a first characteristic of at least a first displacement start (I) at which the armature (9) begins to displace the closure element (11), Generating a second voltage curve different from the first voltage curve and applying the coil according to the second voltage curve, such that in a second curve, depending on a second magnetic flux and a second current, a second characteristic of a second displacement start (I) is more similar to a reference characteristic than the first characteristic, wherein the first characteristic comprises a slope of the first curve, determined by the derivative of the first magnetic flux with respect to the first current, and the second characteristic comprises a slope of the second curve, determined by the derivative of the second magnetic flux with respect to the second current, and wherein the reference characteristic comprises at least one reference slope. [2] Method according to claim 1, wherein the first profile and the second profile are represented by a first curve (31, 37) and a second curve, respectively, in a coordinate system in which the current (i) is plotted along one axis and the magnetic flux (Ψ) is plotted along another axis. [3] Method according to claim 2, wherein the gradient on the respective curve is determined at least at the respective displacement start (I) and / or along at least a portion of an opening movement of the closure element between the displacement start (I) and a contact state (II) in which the armature abuts a pole shoe to terminate the opening movement. [4] Method according to claim 2 or 3, wherein the respective displacement start (I) is identified as a point or region at which a slope of the respective curve changes. [5] Method according to one of claims 3 to 4, wherein the respective contact state (II) is identified as a point or region at which a slope of the respective curve changes. [6] Method according to one of the preceding claims 3 to 5, wherein the loading of the coil according to the second voltage curve takes place before the first contact state (II) and wherein in particular the second voltage curve has a different, in particular extended, shortened or interrupted duration of a boost phase (85) than the first voltage curve. [7] Method according to one of the preceding claims 3 to 5, wherein the loading of the coil according to the second voltage curve takes place after the first contact state (II), wherein in particular the second voltage curve has a different, in particular extended or shortened, duration of a boost phase (85) than the first voltage curve or an interrupted boost phase (85). [8] Method according to one of the preceding claims 3 to 7, wherein the respective characteristic is further determined as a function of at least one section of the respective curve beyond the contact state (II), wherein the second voltage curve is selected such that the section (34) has fewer alternating gradients. [9] Method according to the preceding claim, wherein in order to find the second voltage curve, in particular simulation or testing of the operation of the solenoid valve is carried out, wherein the method in particular further comprises: Providing at least one reference data set (31, 37) comprising a reference curve of current and magnetic flux with sufficiently low bouncing of the armature onto the pole piece. [10] Device (2), in particular engine control unit, for controlling a solenoid valve (1) having a coil (3) and an armature (9) displaceable by magnetic force, by means of which a closure element (11) is displaceable in order to inject fuel (19) into a combustion chamber (23), the device comprising: a driver (4) for applying a voltage (84) according to a first voltage curve to the coil (3) in order to generate a first electrical current (81) through the coil (3); a determination module (6), which for determining a first profile as a function of a first magnetic flux and the first current; and designed to detect, in the first course, a first characteristic of at least one first displacement start (I) at which the armature (9) begins to displace the closure element (11), wherein the driver (4) is further designed to generate a second voltage curve different from the first voltage curve and to apply the coil according to the second voltage curve, such that in a second curve, depending on a second magnetic flux and a second current, a second characteristic of a second displacement start is more similar to a reference characteristic than the first characteristic, wherein the first characteristic comprises a slope of the first curve, determined by the derivative of the first magnetic flux with respect to the first current, and the second characteristic comprises a slope of the second curve, determined by the derivative of the second magnetic flux with respect to the second current, and wherein the reference characteristic comprises at least one reference slope.

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