JP4130840B2 - Method and apparatus for determining the charging edge of a piezoelectric actuator - Google Patents

Description

The present invention relates to a method and apparatus for determining the charging edge of a piezoelectric actuator of at least one injector used to inject a liquid volume into a cavity at high pressure. Said cavity is in particular a combustion chamber of an internal combustion engine.

  From DE 10032022A1, a method for determining the drive control voltage of a piezoelectric actuator of an injection valve is known. Here, the pressure in the hydraulic coupler is first measured indirectly before the next injection process. This pressure is measured by mechanically coupling the piezoelectric actuator to a hydraulic coupler and the pressure induces a corresponding voltage on the piezoelectric actuator. This induced voltage is used to correct the drive control voltage of the piezoelectric actuator before the next injection process. Such injectors are used, for example, in common rail systems. Since the pressure in the hydraulic coupler depends on the rail pressure, the drive control voltage varies depending on the rail pressure. The required voltage of the piezoelectric actuator depends primarily on the pressure in the valve space and the longitudinal expansion of the piezoelectric actuator. The voltage necessary for normal operation of the injector at the operating point is the so-called required voltage, that is, the relationship between the voltage and stroke at a predetermined force proportional to the rail pressure. It is known, for example from DE 103 15815.4, to derive the current required voltage of the injector from the voltage difference between the maximum actuator voltage and the static final voltage.

  It is also known to measure the actuator voltage just before the start of the discharge process and adjust it to a target value to determine the charge edge. A so-called cutoff voltage is used as an adjustment amount for that purpose. This cut-off voltage is the voltage at which the charging process is interrupted when this is reached. In addition, the duration of the charging edge is additionally set to a predetermined target value, usually adjusted to a target value of 100 microseconds.

  Furthermore, it is known from DE 10340137.6 which has not been published before the filing of the present application that the target value of the actuator voltage is adapted to the required voltage of each injector individually for each injector immediately before the start of the discharge process. Yes.

  The problem of the present invention is that the charging edge can be adjusted for each injector so that the effect of parameter tolerances affecting the valve motion can be kept as low as possible, especially compared to the methods known from the prior art. Is to be able to do it.

Advantages of the invention In the method and apparatus of the type described at the outset for determining the filling edge of a piezoelectric actuator, the problem is solved by the following arrangement. That is, the problem is solved by a configuration in which the difference between the cut-off voltage threshold and the steady final voltage is detected and adjusted to a settable target value. According to it, the basic idea of the present invention is that the difference between the cut-off voltage threshold, i.e. the voltage at which the charging process is interrupted when reached, and the steady final voltage, i.e. the voltage of the actuator just before the start of the discharge process, is It is maintained constant by the control circuit. The difference between the cut-off voltage threshold and the actuator voltage just before the start of the discharge process represents a measure of the actuator length change after the end of the charging edge, and thus until the switching valve reaches the stroke stopper after the end of the charging edge. It is also a measure of the distance that must be moved. If this difference is adjusted to be constant, the switching valves of all injectors will have a uniform spacing from each stroke stop at the end of the charging edge.

  In an advantageous embodiment, this difference is arranged to be adjusted to a predetermined target value by changing the charging current at predetermined intervals of the charging time. By maintaining the charging process time constant, it is ensured that the interval between the switching valve and the stroke stopper becomes uniform each time at a predetermined time after the start of the drive control. By doing this, the stroke movement of the switching valve does not actually depend on parameters such as the stroke when the actuator is under no load, the rigidity of the actuator, the rigidity of the actuator-switching valve transmission chain, the valve seat diameter of the switching valve, etc. In addition, the same course characteristic is adjusted for each injector. In addition, in order to do this, it is not necessary to know the parameters. This also allows for implicit injector voltage matching and nominal voltage calibration.

  In yet another embodiment, the difference between the cut-off voltage threshold and the voltage of the actuator immediately before the start of the discharge process is adjusted to a predetermined target value by changing the cut-off voltage threshold. This embodiment is particularly suitable when the setting of the charging current is not quantized with sufficient accuracy or is not set individually for the injector. It is also advantageous here to vary the amount that is known and therefore does not need to be detected additionally.

  Here, advantageously, the charging time is also adjusted to the target value by changing the charging current. Thus, the duration of the charging process is adjusted to the target value by changing the current threshold. In this case, only the accuracy of the charging time to be adjusted depends on how accurately the current threshold is set and whether this can be done individually for the injectors and thus for each cylinder.

Further advantages and configurations from the drawings are described in the following description and illustrated in the figures of the embodiments of the present invention.

  FIG. 1 shows a schematic configuration of an injection valve known from the prior art.

  FIG. 2 is a schematic diagram in which actuator voltage and actuator current during drive control are plotted over time.

  FIG. 3 is a schematic block circuit diagram of a closed loop control device using the method according to the invention.

  FIG. 4 is a schematic block circuit diagram of another closed-loop controller using the method according to the invention.

The illustration 1, a known injection valve 1 from the prior art is shown schematically. This known injection valve 1 is provided with a central bore. In the upper part, an adjustment piston 3 having a piezoelectric actuator 2 is inserted into a central bore, and this adjustment piston 3 is fixedly coupled to the piezoelectric actuator 2. The adjustment piston 3 encloses the hydraulic coupler 4 upward, and an opening having a connection passage to the first seat 6 is provided below. A piston 5 having a valve closing member 12 is disposed on the first seat 6. In this embodiment, the valve closing member 12 is configured as a double-closed control valve. However, the valve closing member 12 may be configured as a single-closed control valve. When the piezoelectric actuator 2 is in the stationary phase, the valve closing member 12 seals the first seat 6. When the actuator 2 is operated, that is, when the drive control voltage U is applied to the terminals + and −, the actuator 2 operates the adjustment piston 3 and the adjustment piston 5 together with the sealing member 12 through the hydraulic coupler 4. Press in the direction of the second sheet 7. Below the second sheet, a nozzle needle 11 is arranged in a corresponding passage. The nozzle needle 11 closes or opens the outlet of the high-pressure channel (common rail pressure) 13 depending on what drive control voltage U is applied. The high pressure is supplied by the injection medium, for example, by the fuel for the internal combustion engine through the supply unit 9, and the supply amount of the injection medium through the supply throttle 8 and the outflow throttle 10 is reduced by the nozzle needle 11 and the hydraulic coupler 4. Controlled by direction. Here, the hydraulic coupler 4 has a function of amplifying the stroke of the adjusting piston 5 and a function of separating the control valve from the static temperature expansion of the actuator 2. The refilling of the hydraulic coupler 4 is not shown here.

  The function of this injection valve will be described in detail below. The adjustment piston 3 moves in the direction of the hydraulic coupler 4 each time drive control of the actuator 2 is performed. At that time, the adjustment piston 5 is moved in the direction of the second sheet 7 together with the sealing member 12, and a part of the medium existing in the hydraulic coupler 4, for example, fuel is pressed out through the gap. Therefore, in order to maintain the reliability of the operation of the hydraulic coupler 4, the hydraulic coupler 4 must be refilled between two injections.

There is a high pressure across the supply flow path 9, which is, for example, between 200 and 2000 bar in the case of a common rail system. This pressure acts on the nozzle needle 11, and the nozzle needle 11 is maintained in a closed state, so that no fuel flows out. Here, when the actuator 2 is operated according to the drive control voltage U and the sealing member 12 moves in the direction of the second sheet, the pressure in the high pressure region disappears, and the nozzle needle 11 opens the injection flow path. What is indicated by P ₁ is the so-called coupler pressure, which is the same as that present in the hydraulic coupler 4. In the hydraulic coupler 4, when there is no drive control U, a static pressure P ₁ is generated. After the actuator 2 is discharged, the coupler pressure P ₁ becomes approximately 0 and is increased again by refilling.

  Here, the stroke and force of the actuator 2 are correlated with the voltage at which the actuator 2 is charged. Since this force is proportional to the rail pressure, the voltage must be adapted to the actuator stroke required to reach the seat 7 reliably depending on the rail pressure. The voltage required for normal operation of the injection valve or injector 1 at the operating point is the so-called required voltage. That is, the relationship between voltage and stroke at a predetermined force proportional to the rail pressure. DE 103 15815.4 discloses how to derive the current individual required voltage of the injector from the voltage difference between the maximum actuator voltage and the static final voltage.

  FIG. 2 schematically illustrates a plot of actuator voltage and actuator current plotted over time.

In the charging edge determination method known from the prior art, the voltage U _{Regel of the} actuator 2 is measured immediately before the start of the discharging process and adjusted to a target value. As an adjustment amount therefor, the so-called cut-off voltage threshold U _abschalt , ie the voltage at which the charging process is interrupted when reached, is used. In addition, the duration of the charging edge is adjusted to a target value Δt _L which is typically 100 microseconds. To make this adjustment, perform open loop control or closed-loop control of the switching threshold I _s of the charging current. Therefore, this switching threshold is used as the adjustment amount. Therefore, in order to change the charging time Δt _L , the charging current I is changed.

The basic idea of the present invention is that instead of the voltage of the actuator 2 just before the start of the discharge process, the difference between the cut-off voltage threshold U _abschalt and the voltage U _Regel of the actuator 2 just before the start of the discharge process is constant by the control circuit. And maintaining it constant by open loop control or closed loop control of the filling edge duration. The difference between the cutoff voltage threshold U _abschalt and the voltage U _Regel of the actuator 2 just before the start of the discharge process is a measure of how the length change of the actuator 2 takes place after the end of the charging edge, In turn, it is also a measure of how far the control valve 12 moves until it reaches the stroke stopper after the end of the shut-off edge. When this difference is adjusted to a constant value, all injector switching valves will have a uniform spacing from the stroke stopper at the end of the charging edge. Furthermore, keeping the charging process time constant also ensures that each of these uniform intervals is achieved at a defined time after the start of drive control. In this way, the stroke motion of the switching valve 12 does not actually depend on parameters such as actuator no-load stroke, actuator stiffness, actuator-valve transmission chain stiffness, valve seat diameter, and the like. Alternatively, the switching valves can be extruded differently so that the movement of the switching valves of the different injectors can each be adjusted to an equal course, and these parameters need not be known.

In the first embodiment shown in FIG. 3, the difference between the voltage of the actuator 2 immediately before the start of the cut-off voltage and the discharge process is adjusted by changing the adjustment amount I _s. The duration of the charging edge is fixedly adjusted by terminating the charging process after a configurable time Δt _L has elapsed. To this, the adjustment amount and the circuit unit 310 is provided for the previous control for I _s, where the rail pressure P _Rail is supplied as an input variable. Furthermore, a circuit module 320 is provided which forms a control circuit for the difference between the cut-off voltage U _abschalt and the voltage U _Regel of the actuator 2 just before the start of the discharge process, which can be set Target value is supplied as an input quantity. The outputs of the circuit units 310 and 320 are added and supplied to the drive control module 330. The drive control module 330 drives and controls the piezoelectric output stage 335, and the piezoelectric output stage 335 supplies the actuator voltage U and the actuator current I of the actuator 2. The piezoelectric output stage 335 further _supplies the cut-off voltage U _abschalt and the voltage U _Regel of the actuator 2 just before the start of the discharge process, and the difference between these is formed at the switching point 340. This difference is supplied to the circuit unit 320, the closed-loop control is performed by changing the adjustment amount I _s. When the current adjustment amount increases, the voltage when the actuator 2 is charged increases, the distance of the valve remaining after the end of the charging process is reduced, and the voltage difference to be adjusted is also reduced. In this case, cut-off voltage U _Abschalt is not set externally, because they are adjusted based on the charge current I _s and the charging time Delta] t _L, the voltage measured at the end of the charging process, cut-off voltage threshold this measurement Must be used as Furthermore, the closed-loop control of the adjustment amount I _s is quantized with sufficient precision, is assumed to be an injector individual turn cylinder individually set.

In another embodiment shown in FIG. 4, the voltage difference to be adjusted between the cut-off voltage threshold U _abschalt and the voltage U _Regel of the actuator 2 just before the start of the discharge process is such that the known cut-off voltage threshold U _abschalt itself This is done by changing. In order to change the cut-off voltage threshold U _abschalt , the charging process must be changed. Therefore, the circuit unit shown in FIG. 4 has a control circuit 410 for charging time, and a settable target value is supplied. Also this device has the circuit unit 420 is provided for pre-controlling the current threshold I _s, the current threshold I _s is supplied to the rail pressure P _Rail as an input variable. The device further includes a circuit unit 430 including a control circuit for the difference between the cut-off voltage threshold U _abschalt and the voltage U _Regel of the actuator 2 just before the start of the discharge process, and for pre-controlling the cut-off voltage threshold U _abschalt A circuit unit 440 is provided. In the circuit point 450, the value _{U Abschalt} output from front control unit 440 for the output value and the cut-off voltage from the control circuit 430 is added, the value of the cut-off voltage threshold _{U Abschalt} is supplied to the drive control module 460 The drive control module 460 controls the drive of the actuator 2 via the piezoelectric output stage 465. That is, the drive control module 460 supplies the actuator voltage U and the actuator current I. The piezoelectric output stage 465 further outputs a signal relating to the duration of the charging process, which is supplied to a circuit unit 410 which forms a control circuit for the charging time. Furthermore, as already described in connection with FIG. 3, the cut-off voltage threshold U _abschalt and the voltage U _Regel of the actuator 2 just before the start of the discharge process are subtracted from each other at circuit point 470, this difference being the cut-off voltage _Supplyed to a circuit unit 430 that includes a control circuit for the difference between the threshold and the voltage U _Regel just before the start of the discharge process. Such duration Delta] t _L of the charging process in the, by changing the current threshold I _s by circuit unit 410 is adjusted to a configurable target value. In this case, only the accuracy of the charging time to be adjusted, and that how exactly it can set the current threshold I _s, this depends on whether it is possible to individually injector individually turn the cylinder. However, this does not adversely affect the accuracy of the control circuit due to the voltage difference.

In a development of the embodiment shown in FIGS. 3 and 4, the control circuit for the difference U _abschalt −U _Regel is switched active only if the control conditions are met. If the control condition is not satisfied, the value of the adjustment amount that was effective when the control condition was finally satisfied in the rail pressure region at that time and the internal combustion engine was operating is the adjustment amount of the control circuit. used. This control condition is, for example, an inspection of whether or not the drive control duration has exceeded a threshold, or whether or not the target value of the injection amount has exceeded the injection amount threshold. When the control circuit is inactive, the adjustment amount is “fixed” as a function of the rail pressure present at that time. By doing so, it is avoided that the control section responds to the falling vibration of the actuator 2 that lasts several hundred microseconds after the end of the charging process, and this falling vibration is reflected in the voltage course of the actuator.

Furthermore, a diagnostic threshold dependent on the rail pressure can be used for the current adjustment amount for adjusting the difference U _abschalt −U _Regel . When the diagnosis threshold value is reached, the associated injector is identified as having a defect. This information is read via the diagnostic interface, for example during maintenance of the internal combustion engine, which greatly simplifies the error search.

1 shows a schematic configuration of an injection valve known from the prior art. FIG. 4 is a schematic diagram in which actuator voltage and actuator current during drive control are plotted over time. Fig. 2 is a schematic block circuit diagram of a closed loop control device using the method according to the invention. FIG. 3 is a schematic block circuit diagram of another closed loop control device using the method according to the present invention.

Claims (10)

A method for determining a charging edge of a piezoelectric actuator (2), comprising:
The piezoelectric actuator (2) is a piezoelectric actuator of at least one injector for injecting an amount of liquid into the cavity at high pressure;
For example, the cavity is a combustion chamber of an internal combustion engine,
A method, characterized in that the difference between the cut-off voltage threshold (U _abschalt ) and the voltage (U _Regel ) of the piezoelectric actuator (2) just before the start of the discharge process is adjusted to a settable target value. In order to adjust the difference between the cut-off voltage threshold (U _abschalt ) and the voltage (U _Regel ) of the piezoelectric actuator (2) just before the start of the discharge process to a settable target value, the charging time (Δt _L ) The method according to claim 1, wherein the charging current threshold (I _s ) is varied at a configurable interval. In order to adjust the difference between the cut-off voltage threshold (U _abschalt ) and the voltage (U _Regel ) of the piezoelectric actuator (2) just before the start of the discharge process to a settable target value, the cut-off voltage threshold (U _abschalt) ) Is varied. The method according to claim 3, wherein the charging time (Δt _L ) is changed by changing a charging current threshold (I _s ) or adjusted to a target value. _{Comparing the} charging current threshold (I _s ) and / or the charging time (Δt _L ) and / or the blocking voltage threshold (U _abschalt ) with a configurable diagnostic threshold;
The method according to any one of claims 1 to 4, wherein the diagnostic threshold is a threshold that, when the diagnostic threshold is reached, is identified as having a defect in the injector. The adjustment of the difference between the cut-off voltage threshold and the voltage immediately before the start of the discharge process is performed only when the control condition is satisfied,
When the control condition is not satisfied, the adjustment that was effective when the internal combustion engine was last operated in the rail pressure region at that time as the control condition was satisfied when the control condition was not satisfied. 6. A method according to any one of claims 1 to 5, wherein a quantity value is used. The method of claim 6 , wherein the control condition is satisfied if a drive control time is greater than a drive control time threshold.   The method according to claim 6, wherein a result of comparison between the target injection amount and the injection amount threshold is used as the control condition. The method according to claim 8 , wherein the control condition is satisfied when an injection amount target value is greater than an injection amount threshold. An apparatus for determining a charging edge of a piezoelectric actuator (2), comprising:
The piezoelectric actuator (2) is a piezoelectric actuator of at least one injector for injecting an amount of liquid into the cavity at high pressure;
For example, the cavity is a combustion chamber of an internal combustion engine.
An apparatus comprising a circuit unit for adjusting a difference between a cut-off voltage threshold (U _abschalt ) and a voltage of the piezoelectric actuator (2) immediately before the start of a discharge process to a settable target value.

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