CN116261624A

CN116261624A - Method for determining the closing time of an injector having a solenoid valve, computer program, controller, internal combustion engine and motor vehicle

Info

Publication number: CN116261624A
Application number: CN202180066594.4A
Authority: CN
Inventors: P·哈克曼; D·莱内韦伯; D·奥格斯特; R·维斯拉蒂
Original assignee: Volkswagen AG
Current assignee: Volkswagen AG
Priority date: 2020-10-30
Filing date: 2021-10-28
Publication date: 2023-06-13
Also published as: DE102020213706A1; WO2022090397A1; EP4237674A1

Abstract

The invention relates to a method for determining the closing time of a solenoid valve of an injector, which is determined by evaluating the logarithmic voltage ratio between a coil voltage and a coil voltage reference value, wherein the coil voltage is the voltage applied to the coil of the solenoid valve.

Description

Method for determining the closing time of an injector having a solenoid valve, computer program, controller, internal combustion engine and motor vehicle

The invention relates to a method for determining the closing time of an injector having a solenoid valve, and to a computer program, a control unit, an internal combustion engine and a motor vehicle.

In an internal combustion engine, an injector is used to directly inject fuel into a combustion chamber. An engine controller controls an on-off valve integrated in the injector to open and close the injector. The injection amount of fuel can be determined by the opening time of the on-off valve.

Electrical control of solenoid injectors may cause delays in opening and closing of these valves. The delay of the individual injectors is caused by the tolerances, as a result of which the injectors have different opening times at the same drive time. Thereby resulting in an undesirable uneven distribution of fuel mass.

It is known to evaluate the (raw) voltage signal during the driving of the injector to determine its closing moment. By the design of the injector, an inflection point coinciding in time with the injector shut-off can be observed. Thus, the inflection point in the voltage signal may be identified taking into account the first or second derivative of the voltage signal. The signal to noise ratio is small due to the second derivative. Therefore, strong filtering or using good measurement techniques must be performed to obtain a signal that is as noise free as possible.

In another approach, the voltage signal may be integrated until a threshold is reached. When the threshold value is reached, this corresponds to the closing moment of the injector.

DE 10 200 9 032 521 A1 describes a method for determining the closing time of a valve with a coil actuator. In this process, the current through the coil of the coil driver is turned off, so that the coil is currentless, and the time profile of the voltage induced in the currentless coil is detected. The induced voltage is generated by decaying eddy currents in the magnetic circuit of the coil driver and the movement of the magnet coil relative to the coil. In addition, a detection time curve of the induced voltage is evaluated, and a closing time is determined from the evaluated time curve.

The object of the present invention is to provide an improved method for determining the closing time of an injector having a solenoid valve, an improved computer program, an improved control unit, an improved internal combustion engine and an improved motor vehicle.

The problem is solved by a method according to claim 1, a computer program according to claim 12, a controller according to claim 13, an internal combustion engine according to claim 14 and a motor vehicle according to claim 15.

Further advantageous designs of the invention result from the dependent claims and the following description of preferred embodiments of the invention.

A first aspect of the invention relates to a method for determining a closing moment of a solenoid valve of an injector. The closing moment is determined by evaluating the logarithmic voltage ratio between the coil voltage and the coil voltage reference. The coil voltage is the voltage applied to the solenoid valve coil.

Injectors with electromagnetic valves (solenoid valve injectors) are used to inject fuel into the combustion chambers of internal combustion engines. The injector is electromagnetically operated. For this purpose, the injector has a coil for generating a magnetic field, so that the coil can be used as an electromagnet. In the rest state of the solenoid valve, in which the coil is not energized and therefore there is no magnetic field, the valve needle is pressed into the valve seat by a pretensioning element (for example a spring) so as to close the valve bore. Thus, the solenoid valve is squeezed or held in a closed (valve) position. To open the solenoid valve, a current (control current) may be applied to the coil, thereby generating a magnetic field. During this opening phase, the magnetic force exceeds the pretension of the pretension element. Thus, during the opening phase, the (magnet) armature driving the valve needle can be moved by the magnetic force counter to the direction of the pretension. This lifts the valve needle from the valve seat, releasing the valve bore, thereby opening the solenoid valve. To close the solenoid, the current to the coil is turned off, whereby the magnetic field is no longer present. Thus, the valve needle is pressed back again by the pretensioning element into the valve seat, the valve opening being blocked, so that the solenoid valve is again in its closed position.

The closing time of the injector is the time when the valve needle is rearranged in the valve seat after the control current (or driving current) is turned off and blocks the valve port, so that the fuel cannot be injected into the combustion chamber.

The coil voltage after switching off the control current corresponds to the induced voltage in the coil, which is additionally generated by the elimination of the magnetic field and the movement of the armature relative to the coil. The coil voltage may be detected using suitable measurement techniques. For example detecting the raw voltage signal.

The reference value is also a voltage value. In some embodiments, the reference value is a voltage value at a measurement start time within one off phase of the coil. The off phase starts after the control current is turned off. In other words, the reference value is the voltage value at the off-time. The off-time is the time at which the control current is turned off.

The "logarithmic voltage ratio between the coil voltage and the reference value" refers to the logarithm of the quotient of the coil voltage divided by the reference value. In some embodiments, natural logarithms may be used.

By using a logarithmic voltage ratio instead of the coil voltage signal, the signal-to-noise ratio for the coil voltage evaluation can be improved. Therefore, the inflection point in the curve of the logarithmic voltage ratio is more easily recognized during discharge. Furthermore, the use of logarithms enables a robust evaluation of the coil voltage with a relatively low computational effort.

In some embodiments, the derivative of the logarithmic voltage ratio may be evaluated to determine the closing time. Wherein the derivative refers to the time derivative of the time curve of the logarithmic voltage ratio.

In a further embodiment, the second derivative of the logarithmic voltage ratio may be evaluated for determining the closing moment. The second derivative here refers to the second derivative of the time curve of the logarithmic voltage ratio. With the second derivative, the curvature characteristic of the time curve of the logarithmic voltage ratio can be evaluated particularly easily. Thus, it is now possible to determine the inflection point or the moment of inflection in the voltage curve (corresponding to the injector closing moment) over time.

Thus, in some embodiments, the closing moment may occur when the second derivative of the logarithmic voltage ratio becomes zero for the first time. It was found that inflection points also occur in the voltage curve when the second derivative of the logarithmic voltage ratio is equal to zero. Thus, by means of a curve interrogation of the logarithmic voltage versus time curve, the inflection point of the voltage curve can be determined particularly simply and computationally.

Furthermore, in certain embodiments, the method may further comprise: the closing moment occurs when the second derivative of the logarithmic voltage ratio remains less than zero for a predetermined time (debounce duration) after reaching a zero value. The predetermined time may be 10 to 50 microseconds (μs). Thus, the predetermined time as the debounce duration may depend on the time interval (measurement interval) of the detection of the voltage raw signal. Thus, in some examples, the debounce duration may be greater than the time interval.

"reach zero" refers to any instant when the second derivative of the logarithmic voltage ratio is equal to zero. In order to make the determination of the closing moment based on the evaluation of the second derivative of the logarithmic voltage ratio more robust, the closing moment is determined or identified as the closing moment if the second derivative remains smaller than zero at least for a predetermined time after such zero point is detected. This ensures that noise generated due to inaccurate measurement is not erroneously identified as a closing point in the time curve of the logarithmic voltage ratio.

As described above, in some embodiments, the reference value may be the voltage applied to the coil at the measurement start time or the off time, respectively.

In a further embodiment, the evaluation of the second derivative of the logarithmic voltage ratio may be performed using an auxiliary function. The extreme points of the auxiliary function may correspond to the closing moments of the injector. The auxiliary functions are as follows:

wherein:

u (t) =coil voltage at time t

U0=reference value/coil voltage at measurement start time or off time

The derivation of the auxiliary function for determining or calculating the second derivative of the logarithmic voltage ratio is as follows.

The voltage discharge curve of the coil (injector) after switching off the control current can be described by the following discharge function:

U(t)＝U ₀ *e ^f(t) (2)

the index f (t) can be determined by variations of the discharge function, resulting in:

the above auxiliary function S (t) is obtained by forming the time derivative of the index f (t).

The first time derivative U' (t) of the discharge function can be approximated by a slope triangle as follows:

wherein the method comprises the steps of

t=time/time variable

Δt=time interval

U (t) =coil voltage at time t

Coil voltage of U (t+Δt) =time t+Δt

The time interval Δt can be used to set the resolution of the detected voltage curve. The coil voltage U (t) is then correspondingly detected at regular time intervals, i.e. at time intervals Δt. For example, the time interval Δt may be from 1 microsecond to 5 microseconds. Thus, the voltage signal of the injector may be recorded with high resolution and stored, for example, in the controller.

If equation (4) is substituted into equation (1), the auxiliary function S (t) can be expressed as follows:

the (absolute) maximum value of the auxiliary function S (t) corresponds to the closing moment of the injector. Furthermore, the auxiliary function S (t) monotonically increases up to a maximum. Thus, the closing moment can be determined by extremum searching in the function S (t). For extremum searching, the first time derivative S' (t) of the auxiliary function S (t) is used, which is related as follows:

equation (6) shows that the first derivative S' (t) of the auxiliary function S (t) corresponds to the second derivative of the logarithmic voltage ratio.

The derivative S' (t) can also be approximated by a slope triangle:

in other embodiments, a sliding average may be used for the detected coil voltage. This means that a running average is formed for the detected coil voltage measurement values, and the above-described evaluation is performed based on the running average of the voltage values. For a sliding time series or a sliding average of the data series, a new set of data points is created, which comprises an average of an equal subset of the original set of data points. With the sliding average value, a voltage signal having less noise than the original voltage signal detected by the detecting device can be generated. This makes the method of evaluating, and thus determining, the closing moment more robust.

In some embodiments, as described above with respect to equation (6), the first derivative S' (t) of the auxiliary function S (t) may correspond to the second derivative of the logarithmic voltage ratio.

In other embodiments, the first derivative of the auxiliary function may be approximated or approximated according to equation (7).

In some embodiments, if the first derivative of the assist function is equal to or less than zero, then there may be a closing time of the injector. The auxiliary function S (t) has the property of being a monotonically increasing function up to the closing moment. Thus, to determine the closing moment, an ending (time) point of the slope of the curve of the auxiliary function can be found. The end point can be determined particularly easily by determining the first derivative of the auxiliary function S' (t). In some embodiments, a closing time exists when the first derivative of the auxiliary function first becomes equal to or less than zero.

In a further embodiment, the evaluation of the logarithmic voltage ratio may be performed during the discharge of the coil throughout the measurement period. Thus, the auxiliary function can also be evaluated over the entire measurement period. In some embodiments, the measurement period may correspond to a period of coil discharge.

A second aspect of the invention relates to a computer program comprising instructions which, when executed by a computer, cause the program to perform the method according to one of the preceding claims. The computer program may be stored on a dielectric storage medium.

A third aspect of the invention relates to a controller arranged to perform one of the above methods.

A fourth aspect of the invention relates to an internal combustion engine. The internal combustion engine may have the above-described injector, and may be controlled by the above-described controller. The internal combustion engine is arranged and trained to perform one of the above methods.

A fifth aspect of the invention relates to a motor vehicle having a controller as described above. The motor vehicle is arranged and trained to perform one of the above methods.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings. In the accompanying drawings:

FIGS. 1a, 1b show solenoid injector schematic diagrams;

FIG. 2 shows a schematic diagram of a voltage curve and a control current curve in a coil;

fig. 3 schematically shows the voltage curve in the coil after the control current is turned off and the curve of the auxiliary function;

fig. 4 shows a method according to a first embodiment;

fig. 5 shows a method according to a second embodiment; and

fig. 6 schematically illustrates a motor vehicle having a controller according to one embodiment.

Fig. 1a schematically shows an exemplary solenoid valve injector (injector) 100 in a shut-off valve position, and fig. 1b shows the injector 100 in an open valve position. The injector 100 has a solenoid valve comprising a valve needle 5 and a valve seat 15. The injector 100 has an electromagnetic actuator for operating a solenoid valve, which comprises a coil 1, an armature 11 and a pretensioning element 13.

The solenoid valve is a normally closed valve. That is, in the unenergized state of the coil 1, the valve needle 5 is arranged on the valve seat 15 in such a manner that the injection ports 17 are shut off by the valve needle 5.

Wherein the pretensioning element 13 is designed to keep the solenoid valve in the off position. For this purpose, the pretensioning element 13 applies a pretensioning force to the valve needle, so that the valve needle 5 is moved in the direction of the valve seat 15 and thus in the closing direction. In the example shown, the pretensioning element 13 is configured as a spring.

The valve needle 5 has a fixed seat 7 and an armature stop 9 for an armature 11, between which the armature 11 is movable. The holder 7 and the armature stop 9 thus define an armature stroke or an armature free stroke relative to the armature 11 of the valve needle 5. Furthermore, the injector 1 has a stroke stop 3 which limits one stroke (valve stroke) of the valve needle 5. In the off-valve position, the armature 11 is located on the fixed seat 7, and in the open-valve position, the armature 11 is connected to the armature stop 9 and the travel stop 3. By applying a magnetic control current I to the coil 1, the armature 11 can be moved from the fixed seat 7 to the armature stop 9. By means of magnetic force, the armature 11 is held on the armature stop 9 such that the armature 11 carries the valve needle 5 against the pretensioning force of the pretensioning element 13, thereby lifting the valve needle 5 off the valve seat 15 until the armature 11 stops on the travel stop 3. Thereby, the injection ports 17 are exposed so that the fuel can be injected into the combustion chamber of the internal combustion engine through the injection ports 17.

Fig. 2 shows a coil voltage diagram 20 for a time profile of the coil voltage U at the coil 1 and a control current diagram 30 for a time profile of the control current I at the coil 1. Fig. 20, 30 very schematically show time curves, in which time is plotted on the horizontal axis and voltage or control current I is plotted on the vertical axis.

Wherein the control current diagram 30 shows the control time t for opening the solenoid valve ₁ Control the application of current I. In this case, immediately after the control time t ₁ The later time curve has steep edges, so that the control current I is at time t ₂ The value of the boost current 31 is reached relatively quickly. t is t ₁ And t ₂ The time between which is also called the boost phase. At time t ₂ The control current I is maximum and the voltage ubinium drops to within the negative range. In addition, the solenoid valve is at the momentt ₂ In an open valve position, wherein the valve lift of the solenoid valve is maximized.

In the boost phase, after an initial steep rise, a flattening of the slope of the control current I can be detected. This is due to the impact of the armature 9 on the valve needle 5, causing the valve needle 6 to lift off the valve seat 15 and the solenoid valve to open. The boost voltage 21 for reaching a steep edge is additionally applied to the injector 100 in the boost stage so that the control current I increases faster than when the battery voltage is applied. The boost voltage 21 may be generated, for example, in a controller and stored in a boost voltage memory, such as a capacitor.

After the boosting phase, from the suction time t ₂ Initially, the control current I is reduced to the holding current value 33. At the slave time t ₂ Extending to a holding time t ₃ Is provided to the injector 100 with the battery voltage. From the holding time t ₃ The hold current phase begins in which the control current I decreases to the hold current 35. In the example shown, at the slave hold time t ₃ Extending to the off time t ₄ Hysteresis 37 may be observed during the current flow during the hold-in current phase.

Control current I at turn-off time t ₄ Shut off, thus reaching a zero value. Thus, the voltage U drops to the off-voltage 25 corresponding to the negative maximum value of the voltage U. As is known, at the switch-off time t ₄ In the discharge curve of the voltage U that then exists, the inflection point 27 in the discharge curve indicates the closing moment of the injector 100.

Fig. 3 shows fig. 40, in which the voltage U across the coil 1 is shown from the off-time t ₄ A starting time profile. Furthermore, a curve S is also plotted for the auxiliary function S (t), by means of which the voltage curve U can be evaluated.

The discharge curve of the voltage U can be described by the following function:

U(t)＝U ₀ *e ^f(t) (2)

as is known, by determining the inflection point 27 in the voltage curve U, the closing moment can be determined.

In accordance with the present disclosure, an alternative method is presented. An auxiliary function S (t) is used instead of the voltage signal. The auxiliary function S (t) is as follows:

measurement experiments show that the maximum 41 of the auxiliary function S (t) corresponds to the inflection point 27 of the voltage curve U. In other words, the instant of maximum 41 corresponds to the inflection point of voltage curve U. The closing moment of the injector can thus be deduced by means of an extremum search in the auxiliary function S (t). For extremum searching, the first derivative S' (t) of the auxiliary function S (t) can be approximately determined by:

fig. 4 shows a method 200 for determining the closing moment of the injector 100 according to the first embodiment, which uses equations (5) and (7) above. The method may be performed by the controller 70.

The method 200 starts with switching off the control current I at a switching off instant t 4.

In 201, a time t (time variable) is set as an off time t ₄ . This corresponds to the time at which the program starts. Further, in 201, the voltage measurement value U (t) or the voltage curve U of the measurement period is retrieved, respectively. In some embodiments, the measurement period may extend from the off-time t4 to the end-time t ₅ Wherein the end time t ₅ Corresponding to the last detection instant of the voltage U (t). The voltage curve U of the measurement period is determined by detecting the voltage value U (t) in a time interval (resolution) Δt using an appropriate measurement technique. Further, as the voltage value U (t), a sliding average value from the detected voltage value may be used.

In 202, the value of the auxiliary function S (t) at time t is determined using equation (5). As described above, the voltage values U (t) and U (t+Δt) at the respective times t and t+Δt can be detected by an appropriate measurement technique.

In 203, the value of the derivative S' (t) of time t is determined using equation (7). The following relationship is obtained by inserting equation (5) into equation (7) of the first derivative S' (t) of the auxiliary function S (t):

as can be seen from equation (6), the first derivative S' (t) of the auxiliary function S (t) corresponds to the second derivative of the logarithmic voltage ratio.

In 204, the function value of the first derivative S' (t) is stored at the corresponding time, for example in the controller 70.

In 205, it is queried whether there are additional measurement points in the voltage curve. This may be done, for example, by checking whether the time t (optionally plus a predetermined time period deltat) is at the end time t _E Previously implemented.

If the query from 205 indicates that there are more measurement points, the method proceeds to 206 where time t is incremented to the next measurement time t+Δt, thus:

t＝t+Δt (9)

after 206, method 200 goes through loop 210, which includes 202, 203, 204, 205, and 206. With the loop 210, the first derivative S' (t) of the auxiliary function S (t) is determined iteratively throughout the measurement period.

At 207, a closing time t of the injector 100 is determined _CT . In one embodiment, a first maximum value of the auxiliary function S' (t) may be determined for this purpose. Thus, it is determined when the first derivative S' (t) of the auxiliary function S (t) is equal to or less than zero for the first time. This moment corresponds to the closing moment t of the injector 100 _CT . Alternatively, a debounce condition may be additionally checked, wherein the first derivative S' (t) of the auxiliary function S (t) is at a predetermined debounce duration Δt ₆ And must be equal to or less than zero. By means of the debounce condition, errors due to measurement inaccuracy and/or noise can be reduced, such that the closing moment t is determined _CT Is more robust. When the debounce condition is not met, i.e. the first derivative S' (t) of the auxiliary function S (t) is shorter than the predetermined debounce duration Deltat ₆ Equal to or less than zero, the next maximum in the auxiliary function S (t) satisfying the debounce condition is searched. Thus, it is closedTime t _CT Corresponding to the moment when the first derivative S' (t) of the auxiliary function S (t) is equal to or smaller than zero for the first time and (optionally) the debounce condition is fulfilled. Thus, if the closing time t is determined _CT The evaluation of the auxiliary function S (t) ends. Thus, the method may be performed in a resource efficient manner in the control unit 70.

In another embodiment, in 207, the closing time t may be determined by searching for a global maximum of the auxiliary function S (t) _CT . The corresponding instant of the global maximum of the auxiliary function S' (t) corresponds to the closing instant t _CT . The extremum search is also based on the evaluation of the first derivative of the auxiliary function S (t), which is performed during the entire measurement period. This method allows a relatively robust determination of the closing time t _CT Because the auxiliary function S' (t) is evaluated over the whole measurement period.

Fig. 5 shows a method 300 for determining the closing moment of the injector 100 according to a second embodiment, which uses equations (5) and (7) above. The method may be performed by the controller 70.

The method 300 starts to switch off the control current I at the switch-off instant t 4.

In

method

300, 301, 302, and 303 perform the same operations as 201, 202, and 203 from method 200.

In 304 it is checked whether the first derivative of the auxiliary function S' (t) is less than or equal to zero at time t.

If it is known from 304 that the first derivative of the auxiliary function S' (t) is not less than or equal to zero at time t, the method proceeds to 305. As with 206 of method 200, in 305, time t is incremented to the next measurement time t+Δt.

After 305, method 300 goes through loop 310, which includes 302, 303, 304, and 305. Loop 310 is used to determine when t first becomes equal to or less than zero for the first time the first derivative of the auxiliary function S' (t).

If it is known from 304 that the first derivative of the auxiliary function S' (t) is less than or equal to zero at time t, the method 300 continues to 306.

At 306, closing time t _CT Is set to time t. In other words, closedTime t _CT Is the moment when the first derivative of the auxiliary function S' (t) is equal to or smaller than zero for the first time.

In 307, the trusted time t is retrieved ₇ . Trusted time t ₇ Indicating the latest possible trusted closing moment at which the shut-off of the injector 100 is allowed to occur. Trusted time t ₇ Depending on the design of the injector 100, it is thus possible, for example, at the driving instant t ₁ Followed by 1200 microseconds to 1800 microseconds. Trusted time t ₇ At the driving time t ₁ And is shown exemplarily in fig. 3 at 1500 microseconds thereafter. In some embodiments, the closing time t (set in 306) _CT And a trusted time t ₇ Can form the debounce duration Δt ₆ 。

In 308, it is determined at the closing time t (set by 306) _CT And between the time of trustworthiness t7, whether there is a greater auxiliary function S (t) in the auxiliary function S (t) than at the closing time t _CT Another one of the maximum values of (a). If (as shown in fig. 3) the closing moment t in the auxiliary function S (t) _CT Without a larger maximum between the time of trustworthiness t7, then in 308 the closing time t is determined or established _CT For the final closing time t _CT . However, if a large maximum exists, it is clear or determined that the maximum is greater than the final closing time t _CT Is a time t of (a).

Fig. 6 schematically illustrates an exemplary controller 70 arranged to perform the above-described method/model. The controller 70 is disposed in a schematic motor vehicle 80 and can control a schematically illustrated internal combustion engine 79. The controller 70 includes a processor 72, a memory (electronic storage medium) 74, and an interface 78. In addition, software (computer program) 76 designed to perform the above-described method is also stored in the memory 74. The processor 72 is designed to execute program instructions of the software 76. The interface 78 is further designed to receive and transmit data. For example, it may be an interface with the CAN bus of the motor vehicle 80, through which the control unit 70 receives signals and sends control commands.

List of reference numerals

1. Coil

3. Travel stop

5. Valve needle

7. Fixing seat

9. Armature stop

11 armature

13. Pretensioning element

15. Valve seat

17. Jet orifice

20. Coil voltage diagram

21. Boost voltage

23. Battery voltage

25. Off voltage

27. Inflection point

30. Control current diagram

31. Boost current

33. To draw in current

35. Holding current

37. Hysteresis of

40 discharge voltage and auxiliary function

41 auxiliary function maximum

50. Circulation

70. Controller for controlling a power supply

72. Processor and method for controlling the same

74 memory (electronic storage medium)

76. Interface

78. Interface

79. Internal combustion engine

80. Motor vehicle

100. Ejector device

200. Method of

201 setting time/time variables and retrieving voltage measurements

202 determining an auxiliary function at time t

203 determining the first derivative of the auxiliary function at time t

204. Storing the function value of the first derivative

205. Querying more measurement points

206 increment time t to the next measurement time

207. Determining closing time

210. Circulation

300. Method of

301 setting time/time variables and retrieving voltage measurements

302 determines an auxiliary function at time t

303 determining the first derivative of the auxiliary function at time t

304 query whether the first derivative of the auxiliary function is equal to or less than zero

305 increment time t to the next measurement time

306. Setting the closing time

307. Retrieval trusted time

309. Determining or defining closing moments

I control current

S auxiliary function

Δt time interval/predetermined duration

Duration of Deltat 6 debounce

t ₁ Control time

t ₂ Time of day

t ₃ Holding time

t ₄ Time of turn-off

t ₅ End time of voltage detection

t _CT Closing time

t7 trusted time instant

U coil voltage

Claims

1. A method for determining the closing time (t) of a solenoid valve of an injector (100) _CT ) The closing time (t _CT ) Is determined by evaluating a logarithmic voltage ratio between a coil voltage and a coil voltage reference value, wherein the coil voltage (U) is a voltage applied to a coil (1) of the solenoid valve.

2. Method according to claim 1, wherein the derivative of the logarithmic voltage ratio (S' (t)) is evaluated to determine the closing moment (t) _CT )。

3. A method according to any preceding claim, wherein the assessment is performedEstimating the second derivative of the logarithmic voltage ratio (S' (t)) to determine the closing moment (t) _CT )。

4. A method according to claim 3, wherein the closing moment (t) occurs when the second derivative (S' (t)) of the logarithmic voltage ratio becomes zero for the first time _CT )。

5. The method of any of the preceding claims, further comprising:

when the second derivative (S' (t)) of the logarithmic voltage ratio reaches zero, it is at a predetermined time (Δt) ₆ ) When the internal hold is less than zero, the closing time (t _CT )。

6. Method according to any one of the preceding claims, wherein the reference value (U0) is the voltage applied to the coil at the moment of measurement start (t 4).

7. Method according to any of the preceding claims, the evaluation of the second derivative (S' (t)) of the logarithmic voltage ratio being performed with an auxiliary function (S (t)), wherein the extreme points of the auxiliary function correspond to the closing moments (tCT) of the injector (100), and the auxiliary function (S (t)) is as follows:

wherein, the liquid crystal display device comprises a liquid crystal display device,

u (t) =coil voltage at time t

U0=time t ₀ Is set to the coil voltage of (2)

8. The method of claim 7, wherein the first derivative of the auxiliary function (S' (t)) corresponds to the second derivative of the logarithmic voltage ratio.

9. A method according to claim 8, wherein the first derivative of the auxiliary function (S' (t)) is approximated as follows:

wherein the method comprises the steps of

S (t) =auxiliary function

t=time instant

Δt=time interval

10. Method according to claim 8 or 9, wherein the closing moment (t) occurs when the first derivative of the auxiliary function (S' (t)) is equal to or smaller than zero _CT )。

11. A method according to any one of the preceding claims, wherein a running average of the coil voltage (U) for detection is used.

12. A computer program (76) comprising instructions which, when executed by a computer, cause it to perform the method according to any of the preceding claims.

13. A controller (70) arranged to perform the method according to any of claims 1 to 11.

14. An internal combustion engine (79) having a controller (70) according to claim 13, wherein the internal combustion engine is arranged and designed for performing the method of any one of claims 1 to 11.

15. A motor vehicle (80) having an internal combustion engine according to claim 14, wherein the motor vehicle (80) is provided and designed for carrying out the method according to any one of claims 1 to 11.