DE10320285A1 - Method for operating an piezoelectric actuator especially for motor vehicle fuel-injection device, requires detecting at least one characteristic of actuator for use in identifying its property class - Google Patents

Abstract

A method for operating a piezoelectric actuator, especially for a fuel injection device (16) of a combustion engine (10), and which comprises a capacitive element and an ohmic resistor connected across it, in which at least one characteristic (dt,V) of the actuator is detected and is used to identify a property class (K1,K2,K3) to which the actuator belongs. The capacitive element is discharged across the ohmic resistance and the voltage during discharge, and at least the time duration (dt) between two given voltage values (V1,V2), is ascertained and used to identify the property class (K1,K2,K3) of the actuator. Independent claims are included for (a) a computer program, for (b) an electric storage medium for control- and/or regulating-device, for (c) a control- and/or regulating device and for (d) a combustion engine, especially for a motor vehicle.

Description

State of technology

The The invention relates initially a method for operating an actuator, in particular for a fuel injection device an internal combustion engine, which has a capacitive element and a includes ohmic resistance parallel to the capacitive element, wherein at least one characteristic of the actuator is detected and on identified a property class based on the recorded characteristic to which the actuator belongs.

The The invention also relates to a corresponding computer program electrical storage medium for a control and / or regulating device an internal combustion engine, such a control and / or regulating device, and one Internal combustion engine.

A method of the type mentioned is from DE 199 58 406 A1 known. A piezo actuator is described there, which can be used, for example, to actuate fuel injectors in internal combustion engines. From the DE 199 58406 A1 it is known that, with the same type of construction, deviations in the properties of one piezo actuator (and / or a fuel injection device) from another can occur. For this reason, the piezo actuators are measured after production and assigned to certain property classes according to their properties. Then an ohmic resistance corresponding to the respective property class is connected to the capacitive element of the piezo actuator in a rigid and non-detachable manner.

To the installation of the injector in an internal combustion engine and its connection via two Lines to a control unit is from the control unit the individual resistance value of the built in the piezo actuator Resistance recorded and from this the corresponding property class of the actuator. The determination of the resistance is correct complex, because initially over a logarithmic interpolation method the decay time of the one hand a capacitive element and on the other hand comprising an ohmic resistance Piezo actuator must be determined. As a result, the Control of the injector or the piezo actuator on the respective property class coordinated control signal are generated, so that the injector, despite the principle-related manufacturing tolerances, with high precision can be operated.

The The present invention has the task of a method of the beginning mentioned type in such a way that it is as easy as possible can be operated.

This In a method of the type mentioned at the outset, the task becomes solved, that the capacitive element over discharge the ohmic resistance, the voltage during the discharge and at least the time period between two specific voltage values is recorded, and based on the captured. Duration the property class of the actuator is identified.

at the task becomes a computer program mentioned at the beginning solved, that it is programmed for use in a method of the type above is.

at An electrical storage medium becomes the task mentioned at the beginning solved by that on it a computer program for use in a process of the above type is stored.

at a control and / or regulating device for one Internal combustion engine solves the problem by using it in a method of the above type is programmed.

at an internal combustion engine, the object is achieved in that it is a control and / or regulating device comprises, which for use in a method of the above Art is programmed.

Advantages of invention

A first advantage of the method according to the invention is that the relatively complex and computationally complex determination of the decay time of the RC element, which is formed by the capacitive element and the ohmic resistance connected in parallel with it, is no longer necessary. Instead, the voltage present is detected during the discharge process of the piezo actuator and the time measured between the passage of two defined voltage thresholds (“trigger thresholds”). This time is characteristic of the property class of a piezo actuator taking into account a tolerance to be determined. The corresponding software can be stored in a central control unit. To increase the accuracy, the number of voltage thresholds, ie the number of time periods to be determined, can be increased and / or several discharge processes can be carried out with corresponding evaluations.

On Another advantage of the method according to the invention is that that with him a tension dependence of capacity of the capacitive element is implicitly taken into account, because the time recording takes place at defined tension ratios. Thus the Classification of the piezo actuator with high accuracy. All in all allows the inventive method on the one hand, the determination of the property class of a piezo actuator or the injector equipped with this on simple and fast way and secondly with great precision.

advantageous Developments of the invention are specified in the subclaims.

In A first further development proposes that the method is applied to a group of actuators, their capacitive Unload elements one after the other and the respective time periods between two voltage values are captured, and being the property class of each actuator based on the time period recorded is identified. This method comes from a Multi-cylinder internal combustion engine used in which the fuel injected directly into the combustion chambers assigned to them by injectors becomes. With the method according to the invention can property classes after installing the injectors in the internal combustion engine of all injectors or the capacitive built into them Elements can be easily determined.

Advantageous is also when the voltage of the actuator is measured via a freewheeling diode becomes. In this case there is a special control of a switch for the Recording of the unloading process is not necessary. The freewheeling diode can also be an integral or intrinsic part of the switch with which the injector is controlled in normal work becomes.

Desirable is also if a decay time of the actuator is chosen to be so long, that dynamic effects of the capacitive element the recorded time can not influence or not significantly. By the cooldown the duration of the unloading process is influenced. This will make the Accuracy of the method according to the invention and thus further improved the classification result.

A particularly advantageous embodiment of the method according to the invention is characterized by the fact that a correction is made, which by a determined temperature or / or an absolutely measured voltage depends and that the correction in identifying the property class of an actuator considered becomes. This allows a particularly high level of identification of property classes, so the differences in resistance values of the ohmic resistance connected in parallel to the capacitive element from one property class to another property class can be smaller. This in turn allows a finer gradation between the property classes and thus ultimately an even more precise control of the actuator. Basis for this is the fact that the temperature of the capacitive element and of the ohmic resistance connected in parallel with this if necessary also the absolute level of the applied voltage can have an impact on the length of time between two Tension levels during of the discharge of the capacitive element passes.

there it is particularly preferred that the actuator in an internal combustion engine is used and the determined temperature is a cooling water temperature and / or a cylinder head temperature and / or an intake air temperature is. At least one of these temperature values is at normal Internal combustion engines recorded anyway, so the high accuracy of the method according to the invention can be achieved without additional components in the Internal combustion engine must be installed.

Around the tension during of being able to detect the unloading with the required precision, it is proposed that the voltage on the actuator during of unloading over a voltage divider is measured, its series resistance value in total at least twice, preferably at least ten times of the resistance value of the ohmic resistance, which is Is part of the actuator. This also makes the precision of a property class elevated, which is smaller gradations between those corresponding to a property class ohmic resistors and thus the overall consideration a larger number property classes.

drawing

following becomes a particularly preferred embodiment of the present Invention with reference to the accompanying drawings in detail explained in more detail. In the drawing shows:

1 is a schematic representation of an internal combustion engine with several fuel injection devices;

2 a simplified circuit diagram showing the control of piezo actuators with which the fuel injectors from 1 be operated; and

3a - 3c a flowchart of a method for identifying property classes of the piezo actuators or fuel injection devices of 1 ,

description of the embodiment

In 1 an internal combustion engine bears the overall reference number 10 , She drives a motor vehicle 12 at which in 1 is only symbolically indicated by a dash-dotted line. The internal combustion engine 10 comprises several combustion chambers 14 , into the fuel injectors associated directly above them 16 is injected. The fuel injectors 16 are on a fuel rail 18 ("Rail") connected. The fuel is stored under high pressure. The fuel manifold 18 is powered by a high pressure fuel supply system 20 fed. The fuel injectors are activated 16 from a control and regulating device 22 , A cylinder head temperature is measured by a sensor 23 detected.

An injection of fuel using a fuel injector 16 into a combustion chamber 14 takes place in that a valve element (not shown) directly or indirectly from a piezo actuator (in 1 not shown) is operated from a closed to an open position and back. In 2 carry the piezo actuators of the individual fuel injection devices 16-1 to 16-m the reference numerals 24-1 to 24 m , They are indicated by a dashed line. However, in 2 for reasons of clarity, only the components of the fuel injection device 16-1 provided with reference numerals.

Any piezo actuator 24 includes as the actual actuator a "piezo stack", which forms a capacitive element and the reference symbol 26 wearing. Parallel to this is every capacitive element 26 an ohmic resistance 28 interconnected, which is also part of the piezo actuator 24 is. A connection 29 of the piezo actuator 24 can via a switch 30 and via a freewheeling diode connected in parallel to this 31 with mass 32 get connected. The other port 33 of the piezo actuator 24 can via a switch 34 with a power supply 36 get connected. A switch 38 enables the connection to be made 33 also with mass 32 ,

Parallel to the connections 29 and 33 is a voltage divider 40 provided, which consists of individual ohmic resistors 42 and 44 exists, which are connected in series. One between the two ohmic resistors 42 and 44 located connection 46 is via an A / D converter (without reference number) with a microcontroller 48 connected. This is also grounded and stands with the control and regulating device 22 in connection. The latter controls the switches 30 . 34 , and 38 on.

For the presence of ohmic resistance 28 there are two reasons: With a piezo actuator 24 it can happen, for example in the event of a cable break, that the valve element actuated by him, without countermeasures, remains in a position in which continuous injection takes place. However, such continuous injection can cause serious damage to the internal combustion engine 10 to lead. To prevent this, the ohmic resistance 28 provided that it also leads to a discharge of the capacitive element in the case of the cable break mentioned above 26 and thus to a return of the piezo actuator 24 in a safe starting position.

Another reason for the presence of ohmic resistance 28 is the way through this ohmic resistance 28 the piezo actuator 24 to "mark" with regard to its belonging to a certain property class. The reason for this is the fact that on the one hand the fuel injectors 16 and on the other hand the capacitive elements 26 Due to their mechanical manufacturing tolerances, the piezo actuators may have different operating behavior from one specimen to another with the same design. This means that without taking appropriate countermeasures men, despite an electrically precise control in the operation of a copy of a fuel injector 16 different amounts of fuel in the combustion chamber 14 the internal combustion engine 10 would arrive.

However, in order to achieve the lowest possible fuel consumption in compliance with strict exhaust gas standards, it is necessary that the fuel injection devices 16 the fuel with the highest possible precision into the combustion chambers assigned to them 14 can bring. As a reduction in the mechanical manufacturing tolerances, the manufacturing cost of the fuel injectors 16 would in an unacceptable manner increase the fuel injectors instead 16 measured after production at certain characteristic operating points with regard to their injection quantity and assigned to a certain property class depending on the measurement result.

After installing the fuel injectors 16 into the internal combustion engine 10 then the property classes of these fuel injectors 16 from the control unit 22 be recognized in the simplest possible way. Then the drive signals with which the fuel injectors 16 or the piezo actuators 24 from the control unit 22 can be controlled, adjusted according to the property classes so that the fuel, despite the manufacturing tolerances, ultimately with very high precision in the individual fuel injection devices 16 assigned combustion chambers 14 can be injected.

The ohmic resistors serve to achieve this goal 28 as the front control and regulating device 22 recognizable "marking" with which the control and regulating device 22 the property class of a fuel injector 16 can recognize. Depending on the property class, there is an ohmic resistance 28 installed with a specific resistance value.

With the piezo actuator 24 , so it's a capacitive element 26 and ohmic resistance 28 comprehensive group, it is an RC link. The course of the voltage during the discharge follows in good approximation the following law:

The relationship for V (T) applies if a diode forward voltage V _{F_Diode is neglected} , if the coupling is only via the diode 31 he follows. In practice, V _{N is} about 100 to 200 times larger than V _{F diode} .

It can be seen that the decay behavior of the voltage V depends on a decay time τ, which in turn depends on the capacitance C of the capacitive element 26 , but above all from the resistance value R _{28 of} the ohmic resistance 28 is dependent. One could now measure the voltage at different times during the decay process and determine the decay duration τ from this by means of logarithmic interpolation. With known capacitance of the capacitive element 26 and known resistance values R ₄₂ and R _{44 of} the ohmic resistors 42 and 44 could be the resistance value R _{28 of} the ohmic resistance 28 determine and thereby the property class of the injector 16 identify. However, this requires a certain amount of computation, and moreover, the capacitance of the capacitive element 26 dependent on the current voltage V and the current temperature T. This makes it difficult to precisely determine the resistance value R _{28 of} the ohmic resistance 28 , In the following with reference to the 3a to 3c The method described is therefore used as an identification criterion for the property class of the injector 16 a period dt is used that elapses between the passage of two voltage thresholds V1 and V2. This is done as follows:
After a starting block 50 is in a block 52 queried whether such operating conditions of the internal combustion engine 10 are available in which the detection of the property classes of the piezo actuators 24-1 to 24 m is possible. Such operating conditions exist, for example, when the speed of the internal combustion engine 10 is zero when the pressure in the fuel rail 18 is equal to the ambient pressure when the control device 22 is on when all switches 30 . 34 and 38 are open when all capacitive elements 26 are discharged and if the control device 22 is in a special learning mode.

In the block 54 all switches are again safe 30 of the piezo actuators 24-1 to 24 m in controlled the open position, as well as the switches 34 and 38 , In the block 56 i is set to 1. Therefore, in the block 58 only the switch 30 of the first piezo actuator 24-1 closed. Then in the block 60 the desk 34 closed and in the block 62 opened again. This will make the capacitive element 26 briefly with the power supply 36 connected and loaded in this way. In the block 64 it is checked whether the voltage V of the capacitive element 26 is charged to the nominal voltage VN. If this is not yet the case, you will be returned to the block 60 , In this way, the capacitive element 26 of the piezo actuator 24-1 by clocked switching of the switch 34 charged to the nominal voltage VN. The switch remains at the end of the charging process 34 open.

About ohmic resistance 28 as well as slightly over the voltage divider 40 the capacitive element begins 26 unload now. The corresponding voltage V on the capacitive element 26 is about the connection 46 and the microcomputer 48 determined. In 66 (See. 3b ) is queried whether the current voltage V has dropped at least to a first voltage threshold V1. This query is repeated until the answer in the block 66 "yes" is. Then in the block 68 a timer started. In the block 70 a query is made as to whether the current voltage V has dropped at least to a second voltage threshold V2. This query is repeated until the answer in the block 70 "yes" is. As long as the answer is in the block 70 is "no", the timer continues to run. When the voltage threshold V2 is reached, the block 72 the time counter is stopped again and the corresponding time value dt is saved.

Then in the block 74 the desk 38 temporarily closed and in the block 76 opened again. As a result, the remaining charge of the capacitive element 26 dissipated. Then in a block 77 corrected the value dt of the time counter based on the signal from the temperature sensor 23 , The absolutely measured voltage V is also in this correction block 77 processed. This makes the temperature dependence of the decay behavior of the voltage on the piezo actuator 24 considered. The result is a corrected time value dtk.

In 78 becomes the switch 30 of the piezo actuator 24-1 reopened (compare 3c ).

In 80 it is queried whether the corrected time value dtk elapsed between the two voltage thresholds V1 and V2 is less than a limit value G1. If this is the case, the piezo actuator 24-1 or the fuel injector 16 assigned property class K1. If this is not the case, the block 82 queried whether the corrected time value dtk is less than a limit value G2, the limit value G2 being greater than the limit value G1. The answer is in the block 82 "Yes," is the piezo actuator 24-1 or the fuel injector L6-1 assigned the property class K2. The answer is in the block 82 "No" is the piezo actuator 24-1 or the fuel injector 16-1 assigned property class K3.

Then in a block 84 queried whether the value i is equal to the maximum value m (the value m corresponds to the number of cylinders of the internal combustion engine 10 or the number of in the internal combustion engine 10 built-in fuel injectors 16 ). The answer is in the block 84 "No" is in the block 86 the value i is increased by 1, and there is a return to the block 58 (see 3a ). This means that the property class is now identified for the cylinder i = 2, i.e. for the piezo actuator 24-2 or the injector 16-2 he follows. The answer is in the block 84 "yes", it means that all piezo actuators 24 or fuel injectors 16 Appropriate property classes have been assigned and the program ends in the block 88 ,

It it should be noted that in an embodiment not shown to increase not only two voltage thresholds V1 and V2 are provided for accuracy are, but a higher one Number of voltage thresholds monitored and / or the process is repeated several times.

In order to be able to use the finest possible gradation of property classes, such ohmic resistances are used in the present exemplary embodiment 28 . 42 , and 44 used, which have only very small tolerances of their resistance values. Furthermore, the series resistance value is R ₄₂ + R _{44 of} the ohmic resistors 42 and 44 about ten times higher than the resistance values R _{28 of} the ohmic resistors 28 of the piezo actuators 24 , In addition, the resistance values R _{28 of} the ohmic resistors 28 chosen so that, on the one hand, the decay time τ is so great that there are significant dynamic effects in the piezo actuator 24 on the same are negligible and the actual injection process is not affected, but on the other hand the capacitive element 26 through the ohmic resistance 28 discharged quickly enough so that the injector closes sufficiently quickly 16 in the event of a line break to the injector 16 is possible.

The freewheeling diode 31 which are parallel to the switch 30 is arranged, can be integrated in an electronic semiconductor switch, specifically intrinsically or in addition to protect the component (for example IGBT). However, the capacitive element can also be used via them 26 also discharged and thus the actuator voltage can be measured, so that the method described above even when the switch is open 30 could be done.

Claims (11)

Method for operating an actuator ( 24 ), in particular for a fuel injection device ( 16 ) an internal combustion engine ( 10 ), which is a capacitive element ( 26 ) and one to the capacitive element ( 26 ) parallel ohmic resistance ( 28 ), wherein at least one characteristic (dt, V) of the actuator ( 24 ) is recorded and on the basis of the recorded characteristic (dt, V) a property class (K1, K2, K3) is identified for which the actuator 24 belongs, characterized in that the capacitive element ( 26 ) via ohmic resistance ( 28 ) discharged, the voltage (V) during the discharge and at least the time period (dt) between two specific voltage values (V1, V2), and on the basis of the recorded time period (dt) the property class (K1, K2, K3) of the actuator ( 24 ) is identified. A method according to claim 1, characterized in that the method for a group of actuators ( 24-1 . 24-2 , ..., 24 m ) is used, the capacitive elements ( 26 ) discharged one after the other and the respective time periods (dt) between two voltage values (V1, V2) are recorded, and the property class (K1, K2, K3) of each actuator ( 24-1 . 24-2 , ..., 24 m ) is identified on the basis of the time period (dt) recorded in each case. Method according to one of the preceding claims, characterized in that the voltage of the actuator ( 24 ) via a free-wheeling diode ( 31 ) is measured. Method according to one of the preceding claims, characterized in that a decay period (τ) of the actuator ( 24 ) is chosen so large that dynamic effects of the capacitive element ( 26 ) cannot influence the recorded time period (dt) or not significantly. Method according to one of the preceding claims, characterized in that a correction is carried out ( 77 ), which depends on a determined temperature and / or an absolutely measured voltage, and that the correction when identifying the property class (K1, K2, K3) of an actuator ( 24 ) is taken into account. A method according to claim 5, characterized in that the actuator ( 24 ) in an internal combustion engine ( 10 ) is used and the determined temperature is a cooling water temperature and / or a cylinder head temperature and / or an intake air temperature. Method according to one of the preceding claims, characterized in that the voltage (V) on the actuator ( 24 ) during discharge via a voltage divider ( 42 . 44 ) is measured, the series resistance value (R ₄₂ , R ₄₄ ) of which is at least twice, preferably at least ten times the resistance value (R ₂₈ ) of the ohmic resistance ( 28 ) which part of the actuator ( 24 ) is. Computer program, characterized in that it programmed for use in a method according to any one of the preceding claims is. Electrical storage medium for a control and / or regulating device ( 22 ) an internal combustion engine ( 10 ), characterized in that a computer program for use in a method of claims 1 to 7 is stored on it. Control and / or regulating device ( 22 ) for an internal combustion engine ( 10 ), characterized in that it is programmed for use in a method according to one of claims 1 to 7. Internal combustion engine ( 10 ), especially for a motor vehicle ( 12 ), with a control and / or regulating device ( 22 ), which is programmed for use in a method according to one of claims 1 to 7.