DE102012211334B4 - Method and device for determining a residual electrical charge of a piezo actuator - Google Patents

Abstract

Method for determining a residual electrical charge of a piezo actuator (12), in which after an electrical charging of the piezo actuator (12), a subsequent active electrical discharge of the piezo actuator (12), the electrical charging and the subsequent active electrical discharge of the piezo actuator ( 12) with a control current (I) with a known time profile, and - a subsequent further discharge of the piezo actuator (12) in a short-circuit operation of the piezo actuator (12), a profile of an estimated value (Q_Resi_EST) of the residual electrical charge of the piezo actuator (12) An end time (t_sc) of the short-circuit operation of the piezo actuator (12) is determined as a function of - a time period (t_charge) for the electrical charging of the piezo actuator (12) and - a time period (t_discharge_sc) for the further discharge of the piezo actuator (12) in the short-circuit operation of the piezo actuator (12).

Description

The invention relates to a method and a corresponding device for determining a residual electrical charge of a piezo actuator.

Piezo actuators are used, for example, as drives for injection valves in internal combustion engines. The piezo actuator can be actuated on the assumption that the piezo actuator is discharged. The piezo actuator is charged, for example, for opening the injection valve and discharged for closing the injection valve.

DE 10 2004 029 906 A1 discloses an injection valve with a piezo actuator, in which, after controlling a nozzle needle back into its closed position and before reaching the closed position, the piezo actuator is electrically short-circuited and reaching the closed position of the nozzle needle is recognized as a function of a significant profile of an electrical current the piezo actuator.

DE 10 2010 022 910 A1 discloses an injection valve in which a first operating phase is carried out for a closing operation of a nozzle needle in a first operating mode, during which a solid-state actuator is discharged to a predetermined partial charge. Furthermore, a second operating phase is carried out during which the solid-state actuator is operated as a sensor. An operating time of the second operating phase is predetermined in such a way that the nozzle needle reaches the closed position during the operating time. A third operating phase is carried out during which the solid-state actuator is further discharged to a predetermined reference state.

The object of the invention is to provide a method and a corresponding device for determining an electrical residual charge of a piezo actuator, which enables a precise and reliable determination of the electrical residual charge of the piezo actuator in a simple manner.

The object is achieved by the features of the independent claims. Advantageous developments of the invention are characterized in the subclaims.

The invention is characterized by a method and a corresponding device for determining a residual electrical charge of a piezo actuator. After an electrical charge of the piezo actuator, a subsequent active electrical discharge of the piezo actuator, and a subsequent further discharge of the piezo actuator in a short circuit operation of the piezo actuator, a course of an estimate of the residual electrical charge of the piezo actuator is determined depending on a period of time from an end time of the short circuit operation of the piezo actuator electrical charging of the piezo actuator and a period of further discharge of the piezo actuator in the short-circuit operation of the piezo actuator. The electrical charging and the subsequent active electrical discharge of the piezo actuator are carried out with a control current with a known time profile.

The electrical charging and the active electrical discharge of the piezo actuator with a control current is carried out with a current source. The further electrical discharge of the piezo actuator in the short-circuit operation takes place with an electrical resistor.

The invention is based on the finding that when the piezo actuator is recharged immediately after the discharge, the energy required to charge the piezo actuator is lower than when the piezo actuator is charged at a later point in time. The energy for charging the piezo actuator depends on the conditions of the previous control. The more charge that is still held in the piezo actuator, the lower the energy required to be recharged to recharge the piezo actuator. This depends on a residual charge in the piezo actuator that has not yet flowed off during the discharge process when charging is started again.

The invention has the advantage that the estimated value of the residual electrical charge of the piezo actuator can be determined precisely. A charge or energy of a subsequent charging process of the piezo actuator can thus be corrected very precisely by the residual charge still present in the piezo actuator after the previous electrical charging and discharging of the piezo actuator has been completed.

In an advantageous embodiment, an estimate of the electrical residual charge of the piezo actuator after the electrical electrical discharge of the piezo actuator is determined as a function of the charging time of the piezo actuator. The course of the estimated value of the residual electrical charge of the piezo actuator from The end time of the short circuit operation of the piezo actuator is determined as a function of the estimated value of the residual electrical charge of the piezo actuator after the electrical electrical discharge of the piezo actuator and the duration of the further discharge of the piezo actuator in the short circuit operation of the piezo actuator. This has the advantage that the estimated value of the residual electrical charge of the piezo actuator can be determined very precisely after the active electrical discharge of the piezo actuator, and thus a basis for determining the estimated value of the remaining electrical charge of the piezo actuator can be very precise at the end time of the short-circuit operation of the piezo actuator can.

In a further advantageous embodiment, the dependence of the estimated value of the residual electrical charge of the piezo actuator after the active electrical discharge of the piezo actuator on the charging duration of the piezo actuator is predetermined by means of an approximation function designed as an exponential function. This has the advantage that the estimated value of the residual electrical charge of the piezo actuator can be determined very simply and nevertheless precisely after the piezo actuator has been actively discharged electrically.

In a further advantageous embodiment, the course of the estimated value of the residual electrical charge of the piezo actuator from the end time of the short-circuit operation of the piezo actuator is predetermined by means of an approximation function designed as an exponential function. This has the advantage that the estimated value of the residual electrical charge of the piezo actuator can be determined very simply and nevertheless precisely at the end time of the short-circuit operation of the piezo actuator.

In a further advantageous embodiment, the course of the estimated value of the residual electrical charge of the piezo actuator is determined from an end time of the short-circuit operation of the piezo actuator as a function of a control duration for the electrical charging and the subsequent active electrical discharge of the piezo actuator with the control current.

In a further advantageous embodiment, the course of the estimated value of the residual electrical charge of the piezo actuator from an end time of the short-circuit operation of the piezo actuator is determined as a function of a discharge time for the active electrical discharge of the piezo actuator and the subsequent further discharge of the piezo actuator in a short-circuit operation of the piezo actuator.

In a further advantageous embodiment, the course of the estimated value of the residual electrical charge of the piezo actuator from an end time of the short circuit operation of the piezo actuator is determined as a function of a time period between the start of the electrical charging of the piezo actuator and the end of the discharge of the piezo actuator in the short circuit operation of the piezo actuator.

In a further advantageous embodiment, the piezo actuator is arranged in an injection valve with a fluid-carrying recess, and the course of the estimated value of the residual electrical charge of the piezo actuator from an end time of the short-circuit operation of the piezo actuator is determined as a function of a hydraulic pressure in the fluid-carrying recess of the injection valve. This has the advantage that forces which act on the piezo actuator from the fluid in the injection valve can be taken into account when determining the estimated value of the residual electrical charge of the piezo actuator at an end time of the short-circuit operation of the piezo actuator.

Exemplary embodiments of the invention are explained below with reference to the schematic drawings.

• 1 ein Einspritzventil und eine Vorrichtung zum Ermitteln einer elektrischen Restladung eines Piezoaktuators,
• 2 ein Schaltbild mit einem Piezoaktuator und einer Ersatzlast,
• 3 ein Diagramm zu einem Ladungsverlauf des Piezoaktuators,
• 4 ein weiteres Diagramm zu einem Ladungsverlauf des Piezoaktuators, und
• 5 ein Ablaufdiagramm eines Programms zum Ermitteln einer elektrischen Restladung des Piezoaktuators.

Show it:

• 1 an injection valve and a device for determining an electrical residual charge of a piezo actuator,
• 2nd a circuit diagram with a piezo actuator and an equivalent load,
• 3rd 1 shows a diagram of a charge profile of the piezo actuator,
• 4th another diagram of a charge profile of the piezo actuator, and
• 5 a flowchart of a program for determining an electrical residual charge of the piezo actuator.

Elements of the same construction or function are identified with the same reference symbols in all figures.

In 1 An injection valve is shown, which is preferably designed as a fuel injection valve and is suitable for injecting fuel into an internal combustion engine. If the injection valve is designed as a fuel injection valve, it is preferably arranged in a cylinder head of the internal combustion engine and measures fuel into a combustion chamber of a cylinder of the internal combustion engine.

In 1 is still a device 100 shown for determining a residual electrical charge of a piezo actuator. The device 100 sensors are assigned which record different measured variables and can determine the value of the measured variables. The device 100 is designed to determine values as a function of at least one of the measured variables, by means of which the residual electrical charge of a piezo actuator can be determined.

The injector has a housing 2nd . The housing 2nd of the injection valve comprises a valve body 4th with a recess 5 and a needle 6 that in the recess 5 of the valve body 4th is inserted and in the valve body 4th is led. In the case 2nd of the injection valve, the fluid can flow towards the valve body 4th be performed. Depending on the position of the needle 6 fuel flows through an injector 8th that are between an area of the tip of the needle 6 and the valve body 4th is formed. The needle is preferred 6 designed to open outwards. However, it can also be designed to open inwards. The needle 6 is by a return spring 10th biased into its closed position. The return spring 10th is with the needle 6 mechanically coupled, and exerts a force on the needle in the closing direction 6 out.

On one of the injection nozzles 8th facing away from the axial end is the needle 8th with a piezo actuator 12th coupled, and cooperates with this. The piezo actuator 12th comprises a stack with piezoelectric elements and two contact pins 14 which are electrically conductively connected to the piezoelectric elements.

2nd shows an electrical circuit with the piezo actuator 12th , a power source 16 , a replacement load 18th and a residual discharge resistor 20th . The power source 16 delivers a drive current I. . The power source 16 has an internal resistance R _i . The replacement load 18th is parallel to the piezo actuator 12th switched. The replacement load 18th is made of an electrically acting capacitor C ₁ and one in parallel with the capacitor C ₁ arranged series circuit from a mechanically acting capacitor C _m , a mechanical inductor L _m and a mechanical resistance R _m built up. The residual discharge resistance 20th is parallel to the equivalent load 18th and to the piezo actuator 12th arranged.

For switching between regulated discharging via the power source 16 and the controlled discharge via the residual discharge resistor 20th releasing heat is a residual discharge switch 22 intended. The residual discharge switch 22 enables switching between discharging the piezo actuator 12th or the equivalent load 18th about the power source 16 and the short circuit operation of the piezo actuator 12th or the equivalent load 18th via the residual discharge resistance 20th .

There is also a diverter switch 24th provided by means of between the piezo actuator 12th and the equivalent load 18th can be switched. The function and meaning of the residual discharge switch 22 and the diverter switch 24th is explained in more detail below.

The electrical circuit of the 2nd is used to determine a residual charge Q_Resi of the piezo actuator 12th used under laboratory conditions. The residual charges determined in this way for various control conditions Q_Resi of the piezo actuator 12th are stored in a map or several maps. The map or the multiple maps for different control conditions are in one 5 schematically shown program for controlling the device for determining the residual electrical charge of the piezo actuator 12th used.

The following is based on the 3rd and 4th first the determination of the remaining charge Q_Resi of the piezo actuator 12th explained in more detail.

• Eine erste Kurve zeigt Messwerte einer ersten Ladung Q1 des Piezoaktuators 12 am Ende eines Entladevorgangs über die Stromquelle 16 jeweils für verschiedene Zeitdauern t_charge des elektrischen Ladens. Zur Messung wird die Ausgangsspannung eines Integrators herangezogen, der den Strom über den Piezoaktuator 12 über die Zeit integriert.

In 3rd are measurements for different time periods t_charge of electrical charging, each for the piezo actuator 12th and the replacement load 18th . The length of time t_charge is the time from the start of charging to the start of discharging the piezo actuator 12th or the equivalent load 18th . 3rd shows four courses of charges Q depending on different values of the duration t_charge of electric charging:

• A first curve shows measured values of a first charge Q1 of the piezo actuator 12th at the end of a discharge process via the power source 16 each for different periods of time t_charge of electric charging. For the measurement, the output voltage of an integrator is used, the current through the piezo actuator 12th integrated over time.

Another curve shows measured values of a second charge Q2 the equivalent load 18th for different periods of time t_charge of electric charging.

Another curve shows values of a third charge Q3 for different periods of time t_charge of electric charging. The values of the third charge Q3 are difference values between the first load Q1 on the piezo actuator 12th and the second charge Q2 at the replacement load 18th . The third charge Q3 corresponds to that of the piezo actuator 12th stored charge at the end of each discharge process via the power source 16 .

Another curve shows the course of values of a fourth charge Q4 depending on the length of time t_charge of electric charging. The curve of the fourth charge Q4 represents an exponential approximation of the course of the values of the third charge Q3 The curve of the fourth charge Q4 corresponds to a function of an estimate Q_Resi_1_EST the residual electrical charge of the piezo actuator 12th after active electrical discharge of the piezo actuator 12th depending on the charging time t_charge of the piezo actuator 12th . The estimate Q_Resi_1_EST the residual electrical charge of the piezo actuator 12th after active electrical discharge of the piezo actuator 12th results preferably according to the formula: $$\begin{array}{l}\text{<figure-callout id="1" label="Q\_Resi\_" filenames="DE102012211334B4\_0004.png,DE102012211334B4\_0005.png" state="{{state}}">Q\_Resi\_</figure-callout>}1\text{\_EST}=\text{Q}\left(\text{I.}\right)*\left(\text{t\_charge}+\text{t\_delta\_charge\_ofs}\right)*\text{FacUnit}*\text{Funct}\\ \text{ResiInc}\end{array}$$

The time t_delta_charge_ofs means that the piezo actuator is still charged due to previous charging processes 12th considered. The FacUnit size takes into account a suitable choice of unit. The size FunctResiInc takes into account a residual charge build-up of the piezo actuator 12th .

Values of this function can be stored in a map.

In 4th is an application example for discharging the piezo actuator 12th shown. The application example is a period of time t_charge the electrical charging of the piezo actuator 12th of 0.237 ms.
4th shows four courses of charges Q . These contain the discharge via the residual discharge resistor 20th and another self-discharge after switching to the high impedance power source 16 . The start of charging at t = 0 ms and the end of the charging process are outside the range shown. The phase of electrical discharge of the piezo actuator 12th ranges from t = 0.237 ms to a point in time t_sc one end of the short-circuit operation. Short-circuit operation via the residual discharge resistor 20th takes place between t = 0.55 ms until the time t sc = 0.65 ms of the end of the short-circuit operation. In short-circuit operation, the residual discharge switch is used 22 a discharge of the piezo actuator 12th or the equivalent load 18th via the residual discharge resistance 20th . After the time t_sc At the end of short-circuit operation, the piezo actuator discharges 12th continues and returns to its original state.

A curve of a charge Q11 makes a measurement on the piezo actuator 12th represents.

The course of the curve of the cargo Q12 shows the measured load on the equivalent load 18th .

The course of the curve of the cargo Q13 is the difference between the cargo Q11 on the piezo actuator 12th and the cargo Q12 at the replacement load 18th , and corresponds to that of the piezo actuator 12th stored cargo.

The course of the cargo Q14 shows an approximation of the shape of the charge curve Q13 by means of an exponential function after the active electrical discharge of the piezo actuator 12th at the time t_sc the end of the short-circuit operation. The course of the estimate Q_Resi_EST the residual electrical charge of the piezo actuator 12th from the end time t_sc the short-circuit operation of the piezo actuator 12th results preferably according to the formula: $$\text{Q\_Resi\_EST}=\text{Q\_Resi\_1\_EST}*\text{FunctResiDec}$$

The size FunctResiDec takes into account a residual charge reduction of the piezo actuator 12th after the end time t_sc the short-circuit operation of the piezo actuator 12th .

Values of this function can be stored in a map.

In a time span t_discharge_sc by the time t_sc At the end of the short-circuit operation, the piezo actuator is discharged 12th in the short circuit operation. Then find in the piezo actuator 12th Discharge processes until a return to the initial state of the piezo actuator 12th instead of.

Takes place in the in the 4th application example shown from a point in time t_ch_2 a new electrical charging of the piezo actuator 12th (in the example at 1.237 ms), at the beginning of this new charging process, it can correspond to the course of the charging Q13 that of the piezo actuator 12th stored charge still a residual charge of about 2.8 µAs in the piezo actuator 12th from the previous loading process. The exponential approximation with the course of the charge Q14 gives an estimate on this point Q_Resi_EST the remaining charge of the piezo actuator 12th of approximately 3 µAs.

An in 5 schematically illustrated program for operating the device for determining the electrical residual charge of the piezo actuator 12th is preferably on a storage medium of the device 100 saved.

The program is preferably in one step S10 started, in which variables are initialized if necessary. This is preferably done when the piezo actuator is started up 12th .

In one step S12 becomes the duration t_charge the electrical charging of the piezo actuator 12th determined. The program is then processed in one step S14 continued.

In one step S14 becomes the estimate Q_Resi_1_EST the residual electrical charge of the piezo actuator 12th after active electrical discharge of the piezo actuator 12th depending on the length of time t_charge the electrical charging of the piezo actuator 12th determined. The program is then processed in one step S16 continued.

In the step S16 becomes the duration t_discharge_sc further discharging the piezo actuator 12th in the short circuit operation of the piezo actuator 12th determined. The program is then processed in one step S18 continued.

In the step S18 becomes the estimate Q_Resi_EST the residual electrical charge of the piezo actuator 12th determined depending on the estimated value Q_Resi_1_EST the residual electrical charge of the piezo actuator 12th after active electrical discharge of the piezo actuator and the time period t_discharge_sc further discharging the piezo actuator 12th in the short circuit operation of the piezo actuator 12th . The estimate Q_Resi_EST the residual electrical charge of the piezo actuator 12th at the time t_ch_2 is used to control a subsequent charging process or several subsequent charging processes Q_ch of the piezo actuator 12th . For this purpose, the amount of the subsequent loading of the piezo actuator 12th energy to be used is reduced by the estimated value Q_Resi_EST the residual electrical charge of the piezo actuator 12th . The processing of the program is then in the step S20 continued.

In the step S20 the program is ended. However, the program is preferably during the operation of the piezo actuator 12th processed regularly.

The advantage of the presented invention is that a precise correction of the charge or energy of a subsequent charging process of the piezo actuator 12th around which is still in the piezo actuator 12th remaining charge is possible after completing a previous completed unloading process. Are the conditions of the control of the piezo actuator 12th known, such as the drive current I. , the activation duration, the duration t_charge of electric charging, the discharge time, the time interval between the charging processes and, if the piezo actuator is used 12th in the injector the hydraulic pressure in the injector, the courses of the estimates Q_Resi_EST the remaining charge can be described via the charging and discharging processes using exponential functions.

Reference list

2nd

casing

4th

Valve body

5

Recess of 4th

6

needle

8th

Injector

10th

Return spring

12th

Piezo actuator

14

Contact pins

16

Power source

18th

Replacement load

20th

Residual discharge resistance

22

Residual discharge switch

24th

Diverter switch

100

Device for determining a residual electrical charge of a piezo actuator

I.

Control current

t_sc

Time of the end of the short-circuit operation

t_charge

Duration of electrical charging

t_ch_2

Time of beginning of another

Charging

gangs

t_discharge_sc

Duration of further unloading

Q

charge

Q1, Q2, Q3, Q4

charge

Q11, Q12, Q13, Q14

charge

Q_Resi

Residual charge

Q_Resi_EST

Estimated residual charge after short-circuit operation

Q_Resi_1_EST

Estimated residual charge at the end of short-circuit operation

R _i

Internal resistance of 16

C ₁

electrically acting capacitor

C _m

mechanically acting capacitor

L _m

mechanical inductance

R _m

mechanical resistance

Claims (9)

Method for determining a residual electrical charge of a piezo actuator (12), in which after - an electrical charge of the piezo actuator (12), - a subsequent active electrical discharge of the piezo actuator (12), the electrical charging and the subsequent active electrical discharge of the piezo actuator ( 12) with a control current (I) with a known time profile, and - a subsequent further discharge of the piezo actuator (12) in a short-circuit operation of the piezo actuator (12), a profile of an estimated value (Q_Resi_EST) of the residual electrical charge of the piezo actuator (12) an end time (t_sc) of the short-circuit operation of the piezo actuator (12) is determined depending on - a time period (t_charge) for the electrical charging of the piezo actuator (12) and - a time period (t_discharge_sc) for the further discharge of the piezo actuator (12) in the short-circuit operation of the piezo actuator (12). Procedure according to Claim 1 , in which - an estimated value (Q_Resi_1_EST) of the residual electrical charge of the piezo actuator (12) after the active electrical discharge of the piezo actuator (12) is determined as a function of the duration (t_charge) of the electrical charging of the piezo actuator (12), and - the course of the Estimated value (Q_Resi_EST) of the residual electrical charge of the piezo actuator (12) from the end time (t_sc) of the short-circuit operation of the piezo actuator (12) is determined depending on the estimated value (Q_Resi_1_EST) of the remaining electrical charge of the piezo actuator (12) after the electrical electrical discharge of the piezo actuator and the duration (t_discharge_sc) of further discharging the piezo actuator (12) in the short-circuit operation of the piezo actuator (12). Procedure according to Claim 2 , in which the dependency of the estimated value (Q_Resi_1_EST) of the residual electrical charge of the piezo actuator (12) after the active electrical discharge of the piezo actuator (12) on the duration (t_charge) of the electrical charging of the piezo actuator (12) is predetermined by means of an approximation function designed as an exponential function . Procedure according to Claim 2 or 3rd , in which the course of the estimated value (Q_Resi_EST) of the residual electrical charge of the piezo actuator (12) from the end time (t_sc) of the short-circuit operation of the piezo actuator (12) is predetermined by means of an approximation function designed as an exponential function. Method according to one of the preceding claims, in which the course of the estimated value (Q_Resi_EST) of the residual electrical charge of the piezo actuator (12) from the end time (t_sc) of the short-circuit operation of the piezo actuator (12) is determined as a function of a control duration for the electrical charging and the subsequent one active electrical discharge of the piezo actuator (12) with the control current (I). Method according to one of the preceding claims, in which the course of the estimated value (Q_Resi_EST) of the residual electrical charge of the piezo actuator (12) is determined from an end time (t_sc) of the short-circuit operation of the piezo actuator (12) as a function of a discharge duration for the active electrical discharge of the piezo actuator (12) and the subsequent further discharge of the piezo actuator (12) in a short-circuit operation of the piezo actuator (12). Method according to one of the preceding claims, in which the course of the estimated value (Q_Resi_EST) of the residual electrical charge of the piezo actuator (12) from an end time (t_sc) of the short-circuit operation of the piezo actuator (12) is determined as a function of a time period between the start of electrical charging of the Piezo actuator (12) until the end of the discharge of the piezo actuator (12) in the short-circuit operation of the piezo actuator (12). Method according to one of the preceding claims, in which the piezo actuator (12) is arranged in an injection valve with a fluid-carrying recess (5), and the course of the estimated value (Q_Resi_EST) of the electrical residual charge of the piezo actuator (12) from an end time (t_sc) the short-circuit operation of the piezo actuator (12) is determined as a function of a hydraulic pressure in the fluid-carrying recess (5) of the injection valve. Device for determining a residual electrical charge of a piezo actuator (12), which is designed after - an electrical charge of the piezo actuator (12), - a subsequent active electrical discharge of the piezo actuator (12), the electrical charging and the subsequent active electrical discharge of the piezo actuator (12) with a control current (I) with a known time profile, and - a subsequent further discharge of the piezo actuator (12) in short-circuit operation of the piezo actuator (12) a profile of an estimated value (Q_Resi_EST) of the residual electrical charge of the piezo actuator (12) to be determined from an end time (t_sc) of the short-circuit operation of the piezo actuator (12) as a function of - a time period (t_charge) for the electrical charging of the piezo actuator (12) and - a time period (t_discharge_sc) of further discharging the piezo actuator (12) in the short-circuit operation of the piezo actuator (12).

Images