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

Abstract

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

Description

[0001] The invention relates to a method for determining a closing time of an injector having a solenoid valve, and to a computer program, a controller, an internal combustion engine and a motor vehicle.

[0002] In internal combustion engines, injectors are used for injecting fuel directly into the combustion chamber. An engine controller controls a switching valve integrated in the injector, thereby opening and shutting the injector. By the opening time of the switching valve, the injection quantity of fuel can be determined.

[0003] The electrical control of solenoid valve injectors can lead to a delay in the opening and closing of these valves. The delay of individual injectors is caused by tolerances, as a result of which the injectors have different opening times at the same actuation time. This leads to an undesired uneven distribution of the fuel quantity.

[0004] It is known to evaluate the (raw) voltage signal during the actuation of the injector in order to determine its closing time. By the design of the injector, a point of inflection can be observed which coincides in time with the closing of the injector. Therefore, the first or second derivative of the voltage signal can be considered to identify the point of inflection in the voltage signal. With the second derivative, the signal-to-noise ratio is small. Therefore, strong filtering must be carried out or good measurement technology must be used in order to obtain a signal which is as noise-free as possible.

[0005] In another method, the voltage signal can be integrated until a threshold value is reached. When the threshold value is reached, this corresponds to the closing time of the injector.

[0006] DE 10 200 9 032 521 A1 describes a method for determining a closing time of a valve having a coil actuator. In this process, the current through the coil of the coil driver is switched off so that the coil is currentless, and a time curve of a voltage induced in the currentless coil is detected. The induced voltage is generated by a decaying eddy current in the magnetic circuit of the coil driver and the movement of the magnetic coil relative to the coil. Furthermore, the detected time curve of the induced voltage is evaluated, and the closing time is determined from the evaluated time curve.

[0007] The technical problem addressed by the invention is to provide an improved method for determining a closing time of an injector having a solenoid valve, an improved computer program, an improved controller, an improved internal combustion engine and an improved motor vehicle.

[0008] The technical problem is solved by the method of claim 1, the computer program of claim 12, the controller of claim 13, the internal combustion engine of claim 14 and the motor vehicle of claim 15.

[0009] Further advantageous designs of the invention result from the subclaims and the following description of preferred embodiments of the invention.

[0010] A first aspect of the present invention relates to a method for determining a closing instant of a solenoid of an injector. The closing instant is determined by evaluating a logarithmic voltage ratio between a coil voltage and a coil voltage reference value. The coil voltage is the voltage applied on the solenoid coil.

[0011] An injector with a solenoid (solenoid injector) is used to inject fuel into a combustion chamber of an internal combustion engine. The injector is electromagnetically operated. To this end, the injector has a coil for generating a magnetic field, so that the coil can be used as an electromagnet. In a rest state of the solenoid, in which the coil is not energized, and thus no magnetic field, the valve needle is pressed into the valve seat by a pre-tensioning element, such as a spring, so that the valve hole is closed. Thus, the solenoid is pressed or held in a closed (valve) position. In order to open the solenoid, a current (control current) can be applied to the coil, so that a magnetic field is generated. During this opening phase, the magnetic force exceeds the pre-tensioning force of the pre-tensioning element. Thus, during the opening phase, a (magnet) armature, which entrains the valve needle, can be moved against the direction of the pre-tensioning force by the magnetic force. This lifts the valve needle from the valve seat, releases the valve hole and thus opens the solenoid. In order to close the solenoid, the current connected to the coil is switched off, whereby the magnetic field no longer exists. Thus, the valve needle is pressed back into the valve seat by the pre-tensioning element again, the valve port is blocked and the solenoid is again in its closed valve position.

[0012] The closing instant of the injector is the instant at which the valve needle repositions in the valve seat and blocks the valve port after the control current (or drive current) is switched off, so that fuel cannot be injected into the combustion chamber.

[0013] The coil voltage after the control current is switched off corresponds to an 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 can be detected with suitable measurement technology. For example, the raw voltage signal is detected.

[0014] The reference value is also a voltage value. In some embodiments, the reference value is the voltage value at the beginning of a de-energization phase of the coil. The de-energization phase starts after the control current is switched off. In other words, the reference value is the voltage value at the de-energization instant. The de-energization instant is the instant at which the control current is switched off.

[0015] 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 certain embodiments, the natural logarithm can be used.

[0016] By using the logarithmic voltage ratio instead of the coil voltage signal, the signal-to-noise ratio for the coil voltage evaluation can be improved. Thus, the inflection point in the curve of the logarithmic voltage ratio is easier to identify during the discharge process. Furthermore, the use of the logarithm enables a robust evaluation of the coil voltage with a relatively low computational effort.

[0017] In some embodiments, the derivative of the logarithmic voltage ratio can be evaluated to determine the closing instant. Here, the derivative refers to the first derivative of the time curve of the logarithmic voltage ratio.

[0018] In further embodiments, the second derivative of the logarithmic voltage ratio can be evaluated for determining the closing instant. Here, the second derivative refers to the second derivative of the time curve of the logarithmic voltage ratio. With the second derivative, the curvature properties of the time curve of the logarithmic voltage ratio can be evaluated particularly easily. Thus, now a point of inflection or the instant of the point of inflection in the voltage curve of the time (corresponding to the closing instant of the injector) can be determined.

[0019] Thus, in some embodiments, the closing instant can occur when the second derivative of the logarithmic voltage ratio first becomes zero. It is found that when the second derivative of the logarithmic voltage ratio equals zero, also a point of inflection in the voltage curve occurs. Thus, by a curve review of the time curve of the logarithmic voltage ratio, the point of inflection of the voltage curve can be determined particularly simply and computationally.

[0020] Further, in certain embodiments, the method can also comprise that the closing instant 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 can be 10 to 50 microseconds (ps). Thus, the predetermined time as debounce duration can depend on the time interval (measurement interval) of the detection of the voltage raw signal. Thus, in certain examples, the debounce duration can be greater than the time interval.

[0021] “Reaching a zero value” refers to any instant at which the second derivative of the logarithmic voltage ratio equals zero. To make the determination of the closing instant based on the evaluation of the second derivative of the logarithmic voltage ratio more robust, the closing instant is determined or identified if, after detecting such a zero point, the second derivative remains less than zero at least for a predetermined time. This can ensure that noise in the time curve of the logarithmic voltage ratio due to measurement inaccuracies is not falsely identified as a closing point.

[0022] As mentioned above, in some embodiments, the reference value can be the voltage applied on the coil at the measurement start instant or at the switch-off instant, respectively.

[0023] In further embodiments, the evaluation of the second derivative of the logarithmic voltage ratio can be performed using a helper function. The extremum point of the helper function can correspond to the closing instant of the injector. The helper function is as follows:

[0024]

[0025] wherein:

[0026] U(t) = coil voltage at instant t

[0027] U0 = reference value / coil voltage at the moment of start of measurement or at the moment of switch-off

[0028] The derivation of the auxiliary function for determining or calculating the second derivative of the logarithmic voltage ratio is described as follows.

[0029] The voltage discharge curve of the coil (injector) after the switch-off control current can be described by the following discharge function:

[0030] U(t) = U0 * e f(t) (2)

[0031] The exponential f(t) can be determined by a modification of the discharge function, so that:

[0032]

[0033] By forming the time derivative of the exponential f(t), the above auxiliary function S(t) is obtained.

[0034]

[0035] The first time derivative U'(t) of the discharge function can be approximated by a slope triangle as follows:

[0036]

[0037] where

[0038] t = time variable

[0039] Δt = time interval

[0040] U(t) = coil voltage at the moment t

[0041] U(t + Δt) = coil voltage at the moment t + Δt

[0042] The time interval Δt can be used to set the resolution of the detection of the voltage curve. The coil voltage U(t) is then detected at regular time intervals, i.e. with the time interval Δt. For example, the time interval Δt can be from 1 microsecond to 5 microseconds. Thus, the voltage signal of the injector can be recorded with high resolution and, for example, stored in the controller.

[0043] If equation (4) is inserted into equation (1), the auxiliary function S(t) can be represented as follows:

[0044]

[0045] The (absolute) maximum of the auxiliary function S(t) corresponds to the closing time of the injector. Furthermore, the auxiliary function S(t) is monotonically increasing until the maximum. Thus, the closing time can be determined by an extremum search in the function S(t). For the extremum search, the first time derivative S'(t) of the auxiliary function S(t) is used, which is related as follows:

[0046]

[0047] 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.

[0048] The derivative S'(t) can also be approximated with a slope triangle:

[0049]

[0050] In other embodiments, a sliding average can be used on the detected coil voltage. This means that a sliding average is formed for the detected coil voltage measurements, and the above evaluation is carried out on the basis of the sliding average of the voltage values. For a sliding average for a sliding time series or data series, a new data point set is created, which comprises the average values of equal subsets of the original data point set. With the sliding average, it is possible to produce a voltage signal that is less noisy than the original voltage signal detected by the detection device. This makes the evaluation, and thus the method of determining the closing time, more robust.

[0051] In some embodiments, as described above with respect to equation (6), the first derivative S'(t) of the auxiliary function S(t) can correspond to the second derivative of the logarithmic voltage ratio.

[0052] In other embodiments, the first derivative of the auxiliary function can be approximated or approached according to equation (7).

[0053] In some embodiments, if the first derivative of the auxiliary function is equal to or less than zero, there can be a closing time of the injector. The auxiliary function S(t) has the property of being a monotonically increasing function until the closing time. Thus, in order to determine the closing time, one can look for an end point of the slope of the curve of the auxiliary function. The end point can be determined particularly easily by taking the first derivative of the auxiliary function S'(t). In some embodiments, the closing time is present when the first derivative of the auxiliary function first becomes equal to or less than zero.

[0054] In further embodiments, the evaluation of the logarithmic voltage ratio can be carried out over the entire measurement period during the discharge of the coil. Thus, the auxiliary function can also be evaluated over the entire measurement period. In some embodiments, the measurement period can correspond to the period of the coil discharge.

[0055] A second aspect of the application relates to a computer program comprising commands which, when the program is executed by a computer, cause it to carry out the method according to one of the preceding claims. The computer program can be stored on an electronic storage medium.

[0056] A third aspect of the application relates to a controller arranged to carry out one of the above methods.

[0057] A fourth aspect of the application relates to an internal combustion engine. The internal combustion engine can have the above-described injector and can be controlled by the above-described controller. The internal combustion engine is arranged and trained to carry out one of the above-described methods.

[0058] A fifth aspect of the application relates to a motor vehicle having the above-described controller. The motor vehicle is arranged and trained to carry out one of the above-described methods.

[0059] Embodiments of the application will now be described in an exemplary manner and with reference to the accompanying drawings. In the drawings:

[0060] Figure 1a 、 1b A schematic diagram of an electromagnetic valve injector is shown;

[0061] Figure 2 A schematic diagram of the voltage curve in the coil and the control current curve is shown;

[0062] Figure 3 The voltage curve in the coil after the control current has been switched off and the curve of the auxiliary function are shown schematically;

[0063] Figure 4 A method according to a first embodiment is shown;

[0064] Figure 5 A method according to a second embodiment is shown; and

[0065] Figure 6 A motor vehicle having a controller according to an embodiment is shown schematically.

[0066] Figure 1a An exemplary electromagnetic valve injector (injector) 100 in the closed valve position is shown schematically, Figure 1b The injector 100 in the open valve position is shown. The injector 100 has an electromagnetic valve which comprises a valve needle 5 and a valve seat 15. The injector 100 has an electromagnetic actuator for operating the electromagnetic valve, which comprises a coil 1, an armature 11 and a pre-tensioning element 13.

[0067] The electromagnetic valve is a normally closed valve. That is to say, in the de-energized state of the coil 1, the valve needle 5 is arranged on the valve seat 15 in such a way that the injection opening 17 is closed by the valve needle 5.

[0068] The pre-tensioning element 13 is designed to keep the solenoid valve in the closed position. To this end, the pre-tensioning element 13 exerts a pre-tensioning force on the valve needle 5, which moves in the direction of the valve seat 15, thus in the closing direction. In the example shown, the pre-tensioning element 13 is configured as a spring.

[0069] The valve needle 5 has a fixed seat 7 and an armature stop 9 for the armature 11, between which the armature 11 can move. The fixed seat 7 and the armature stop 9 thus define an armature stroke or armature free stroke of the armature 11 relative to the valve needle 5. In addition, the injector 1 has a stroke stop 3 which limits a stroke of the valve needle 5 (valve stroke). In the closed valve position, the armature 11 is located on the fixed seat 7, in the open valve position the armature 11 is connected to the armature stop 9 and the stroke stop 3. By applying a magnetic force on the coil 1, the current I can be moved from the fixed seat 7 to the armature stop 9. By means of the magnetic force, the armature 11 is held on the armature stop 9, so that the armature 11 carries the valve needle 5 against the pre-tensioning force of the pre-tensioning element 13, thus lifting the valve needle 5 from the valve seat 15 until the armature 11 stops on the stroke stop 3. As a result, the injection opening 17 is exposed, so that fuel can be injected through the injection opening 17 into the combustion chamber of the internal combustion engine.

[0070] Figure 2 A coil voltage diagram 20 for the time profile of the coil voltage U at the coil 1 and a control current diagram 30 for the time profile of the control current I at the coil 1 are shown. The diagrams 20, 30 represent the time profiles very schematically, wherein time is plotted on the horizontal axis and the voltage or the control current I on the vertical axis.

[0071] The control current diagram 30 shows the application of the control current I for the control time t1 for opening the solenoid valve. In this case, the time profile immediately after the control time t1 has a steep edge, so that the control current I reaches the value of the boost current 31 relatively quickly at the time t2. The time between t1 and t2 is also referred to as boost phase. At the time t2, the control current I is at its maximum and the voltage U is at its minimum and falls into the negative range. In addition, the solenoid valve is in the open valve position at the time t2, in which the valve lift of the solenoid valve is at its maximum.

[0072] In the boost phase, after the initially 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, so that the valve needle 6 is lifted from the valve seat 15 and the solenoid valve is opened. In addition to the boost voltage 21 for achieving the steep edge, a boost voltage 21 is applied to the injector 100 in the boost phase, so that the control current I increases faster than when the battery voltage is applied. The boost voltage 21 can be generated, for example, in a controller and stored in a boost voltage store, for example, a capacitor.

[0073] After the boost phase, from the time of the catch t2, the control current I is reduced to a catch current value 33. In the catch current phase, which extends from the time t2 to the hold time t3, the battery voltage is supplied to the injector 100. From the hold time t3, a hold current phase is started, in which the control current I is reduced to a hold current 35. In the example shown, during the hold current phase, which extends from the hold time t3 to the switch-off time t4, a hysteresis 37 can be observed in the current course.

[0074] The control current I is switched off at the switch-off time t4, so that it reaches a value of zero. As a result, the voltage U falls to a switch-off voltage 25, which corresponds to the negative maximum value of the voltage U. It is known that in the discharge curve of the voltage U, which exists after the switch-off time t4, an inflection point 27 in the discharge curve indicates the closing time of the injector 100.

[0075] Figure 3 A diagram 40 is shown, in which the time curve of the voltage U on the coil 1 is shown from the switch-off time t4. In addition, a curve S is also plotted for the auxiliary function S(t), by means of which the voltage curve U can be evaluated.

[0076] The discharge curve of the voltage U can be described by the following function:

[0077] U(t) = U0 * e f(t) (2)

[0078] It is known that by determining the inflection point 27 in the voltage curve U, the closing time can be determined.

[0079] According to the present disclosure, an alternative method is proposed. Instead of the voltage signal, an auxiliary function S(t) is used. The auxiliary function S(t) is as follows:

[0080]

[0081] Measurement experiments have shown 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 time of the maximum 41 corresponds to the inflection point of the voltage curve U. Thus, the closing time of the injector can be inferred by an extremum search in the auxiliary function S(t). For the extremum search, the first derivative S'(t) of the auxiliary function S(t) can be determined approximately by the following method:

[0082]

[0083] Figure 4 A method 200 for determining the closing time of the injector 100 according to a first embodiment is shown, which uses the above equations (5) and (7). The method can be performed by the controller 70.

[0084] The method 200 starts with a switched-off control current I at the switch-off time t4.

[0085] In 201, the time instant t (time variable) is set to the switch-off time instant t4. This corresponds to the time at which the program starts. Furthermore, 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 can extend from the switch-off time instant t4to the end time instant t5, wherein the end time instant t5corresponds to the last detection time instant of the voltage U(t). The voltage curve U of the measurement period is determined by detecting the voltage values U(t) in the time interval (resolution) At using appropriate measurement techniques. Furthermore, for the voltage values U(t), also a sliding average from the detected voltage values can be used.

[0086] In 202, the value of the auxiliary function S(t) at the time instant t is determined using equation (5). As mentioned above, the voltage values U(t) and U(t+At) at the respective time instants t and t+At can be detected by appropriate measurement techniques.

[0087] In 203, the value of the derivative S'(t) at the time instant t is determined using equation (7). By inserting the first derivative S'(t) of the auxiliary function S(t) into equation (7), the following relation is obtained:

[0088]

[0089] 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.

[0090] In 204, the function value of the first derivative S'(t) is stored at the respective time instant, e.g. in the controller 70.

[0091] In 205, it is inquired whether there are further measurement points of the voltage curve. This can be achieved, for example, by checking whether the time instant t (optionally plus a predetermined time length At) is before the end time instant t E

[0092] If the inquiry from 205 indicates that there are further measurement points, the method proceeds to 206, wherein the time instant t is incremented to the next measurement time instant t+At, thus:

[0093] t = t + At (9)

[0094] After 206, the method 200 undergoes a loop 210, which comprises 202, 203, 204, 205 and 206. With the loop 210, the first derivative S'(t) of the auxiliary function S(t) is determined iteratively over the entire measurement period.

[0095] In 207, the closure time instant t CT ​In one embodiment, a first maximum of the auxiliary function S'(t) can be determined for this purpose. Thus, it is determined when the first derivative S'(t) of the auxiliary function S(t) first equals or is less than zero. This time corresponds to the closing time t CT Optionally, a further de-bounce condition can be checked, in which the first derivative S'(t) of the auxiliary function S(t) must equal or be less than zero for a predetermined de-bounce duration At6. By this de-bounce condition, errors due to measurement inaccuracies and / or noise can be reduced, making the method of determining the closing time t CT more robust. When the de-bounce condition is not fulfilled, i.e. the first derivative S'(t) of the auxiliary function S(t) is equal or less than zero for less than the predetermined de-bounce duration At6, the next maximum in the auxiliary function S(t) is searched for which fulfills the de-bounce condition. Thus, the closing time t CT corresponds to the time at which the first derivative S'(t) of the auxiliary function S(t) first equals or is less than zero and (optionally) fulfills the de-bounce condition. Thus, if the closing time t CT is determined, the evaluation of the auxiliary function S(t) ends. Thereby, this method can be performed in a resource-efficient manner in the control unit 70.

[0096] In another embodiment, in 207, the closing time t CT may be determined by searching for a global maximum of the auxiliary function S(t). The respective time of the global maximum of the auxiliary function S'(t) corresponds to the closing time t CT The extremum search is also based on an evaluation of the first derivative of the auxiliary function S(t), which is performed over 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 entire measurement period.

[0097] Figure 5 A method 300 for determining the closing time of the injector 100 according to the second embodiment is shown, which uses the above equations (5) and (7). This method can be performed by the controller 70.

[0098] The method 300 starts with the shut-off control current I at the shut-off time t4.

[0099] In the method 300, 301, 302 and 303 perform the same operations as 201, 202 and 203 from the method 200.

[0100] In 304, it is checked whether the first derivative of the auxiliary function S'(t) is less than or equal to zero at the time t.

[0101] 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 the time instant t, the method proceeds to 305. As in 206 of the method 200, in 305 the time instant t is incremented to the next measurement time instant t + At.

[0102] After 305, the method 300 undergoes a loop 310 comprising 302, 303, 304 and 305. The loop 310 serves to determine at which time instant t the first derivative of the auxiliary function S'(t) first becomes equal to or less than zero.

[0103] If it is known from 304 that the first derivative of the auxiliary function S'(t) is less than or equal to zero at the time instant t, the method 300 proceeds to 306.

[0104] In 306, the closing time instant t CT is set to the time instant t. In other words, the closing time instant t CT is the time instant at which the first derivative of the auxiliary function S'(t) is equal to or less than zero for the first time.

[0105] In 307, the trustworthiness time instant t7is retrieved. The trustworthiness time instant t7indicates the latest possible trustworthiness closing time instant at which the deactivation of the injector 100 is allowed to occur. The trustworthiness time instant t7depends on the design of the injector 100 and can thus for example be between 1200 microseconds and 1800 microseconds after the driving time instant tl. The trustworthiness time instant t7is exemplarily shown in Figure 3 at 1500 microseconds after the driving time instant tl. In some embodiments, the time span of the closing time instant t CT (set in 306) and the trustworthiness time instant t7may form a de-bounce duration At6.

[0106] In 308, it is determined whether there is another maximum in the auxiliary function S(t) between the closing time instant t CT (set by 306) and the trustworthiness time instant t7that is larger than the maximum of the auxiliary function S(t) at the closing time instant t CT . If there is no larger maximum in the auxiliary function S(t) between the closing time instant t CT and the trustworthiness time instant t7(as shown in Figure 3 ), the closing time instant t CT is determined or determined to be the final closing time instant t CT . However, if there is a larger maximum, the time instant t at which the maximum is larger than the final closing time instant t CT is explicitly or determined.

[0107] Figure 6An exemplary controller 70, which is configured to execute the above-described method / model, is shown schematically. The controller 70 is arranged in a motor vehicle 80 of the schematic drawing and can control an internal combustion engine 79, which is also shown schematically. The controller 70 comprises a processor 72, a memory (electronic storage medium) 74 and an interface 78. Furthermore, a software (computer program) 76, which is designed to execute the above-described method, is also stored in the memory 74. The processor 72 is designed to execute the program instructions of the software 76. The interface 78 is further designed to receive and send data. For example, it can be an interface to the CAN bus of the motor vehicle 80, through which the control unit 70 receives signals and sends control commands.

[0108] List of reference signs

[0109] 1 coil

[0110] 3 stroke stop

[0111] 5 valve needle

[0112] 7 fixing seat

[0113] 9 armature stop

[0114] 11 armature

[0115] 13 pre-tensioning element

[0116] 15 valve seat

[0117] 17 injection opening

[0118] 20 coil voltage diagram

[0119] 21 boost voltage

[0120] 23 battery voltage

[0121] 25 cut-off voltage

[0122] 27 inflection point

[0123] 30 control current diagram

[0124] 31 boost current

[0125] 33 inhalation current

[0126] 35 maintenance current

[0127] 37 hysteresis

[0128] 40 diagram of discharge voltage and auxiliary function

[0129] 41 maximum value of auxiliary function

[0130] 50 cycle

[0131] 70 controller

[0132] 72 processor

[0133] 74 memory (electronic storage medium)

[0134] 76 interface

[0135] 78 interface

[0136] 79 internal combustion engine

[0137] 80 motor vehicle

[0138] 100 injector

[0139] 200 method

[0140] 201 setting a time variable and retrieving voltage measurement values

[0141] 202 determining an auxiliary function at time t

[0142] 203 determining a first derivative of the auxiliary function at time t

[0143] 204 storing a function value of the first derivative

[0144] 205 querying for more measurement points

[0145] 206 incrementing time t to the next measurement time

[0146] 207 determining a closing time

[0147] 210 loop

[0148] 300 method

[0149] 301 setting a time variable and retrieving voltage measurement values

[0150] 302 determining an auxiliary function at time t

[0151] 303 determining a first derivative of the auxiliary function at time t

[0152] 304 querying whether the first derivative of the auxiliary function is equal to or less than zero

[0153] 305 incrementing time t to the next measurement time

[0154] 306 setting a closing time

[0155] 307 retrieving a plausibility time

[0156] 309 explicitly or determining a closing time

[0157] I control current

[0158] S auxiliary function

[0159] Δt time interval / predetermined duration

[0160] Δt6 de-bounce duration

[0161] t1 control instant

[0162] t2 instant

[0163] t3 hold instant

[0164] t4 turn-off instant

[0165] t5 end of voltage detection instant

[0166] t CT closing instant

[0167] t7 trustworthiness instant

[0168] U coil voltage

Claims

1. A method for determining a closing instant (t CT ) of a solenoid of an injector (100), the closing instant (t CT ) being 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, wherein, The second derivative of the log voltage ratio (S'(t)) is evaluated to determine the closing time (t CT ).

2. The method of claim 1, wherein, The closing time (t CT ) occurs when the second derivative of the logarithmic voltage ratio (S'(t)) first becomes zero.

3. The method according to claim 1 or 2, characterized in that, The method further comprises: When the second derivative of the logarithmic voltage ratio (S'(t)) remains less than zero for a predetermined time (Δt6) after reaching zero, the closing time (t CT ) is determined to have occurred.

4. The method of claim 1, wherein, The coil voltage reference value (U0) is the voltage applied on the coil at the beginning of the measurement instant (t4).

5. The method of claim 1, wherein, The evaluation of the second derivative of the logarithmic voltage ratio (S'(t)) is performed with the help of an auxiliary function (S(t)), wherein the extreme points of the auxiliary function correspond to the closing instant (tCT) of the injector (100) and the auxiliary function (S(t)) is as follows: wherein U(t) = coil voltage at instant t U0 = coil voltage at instant t0.

6. The method of claim 5, wherein, The first derivative of the auxiliary function (S'(t)) corresponds to the second derivative of the logarithmic voltage ratio.

7. The method of claim 6, wherein, The first derivative of the auxiliary function (S'(t)) is approximated as follows: wherein S(t) = auxiliary function t = instant Δt = time interval.

8. The method according to claim 6 or 7, characterized in that, The closing time (t CT ) occurs when the first derivative of the auxiliary function (S'(t)) is equal to or less than zero.

9. The method of claim 1, wherein, A sliding average of the coil voltage (U) for the detection is used.

10. A computer program product (76) comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method according to any one of the preceding claims.

11. A controller (70) arranged to carry out the method according to any one of claims 1 to 9.

12. An internal combustion engine (79) having a controller (70) according to claim 11, wherein the internal combustion engine is arranged and designed to carry out the method according to any one of claims 1 to 9.

13. A motor vehicle (80) having an internal combustion engine according to claim 12, wherein the motor vehicle (80) is arranged and designed to carry out the method according to any one of claims 1 to 9.

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