EP1450028A2 - Method and apparatus for monitoring a piezoelectric actuator - Google Patents

Abstract

The method involves determining (140) a characteristic of the actuator, comparing (150) the determined characteristic with an expected characteristic and identifying a fault in the injector if there is a deviation between the determined and anticipated characteristics. It involves detecting charging values and associated voltage values during a charging process and/or a discharging process. Independent claims are also included for the following: (a) an arrangement for implementing the inventive method (b) and a method monitoring a piezoelectric actuator (c) a computer program for implementing the inventive method (d) a computer program product for implementing the inventive method (e) and a digital storage medium for interaction with a programmable computer system.

Description

The invention relates to a method and a device for monitoring a piezoelectric actuator according to the preambles of the independent claims.

A method and an apparatus for measuring the voltage of a piezoelectric Actuator is known from EP 11 38 902. Such actuators are used in particular Control of an injector used, in particular to control the Serve fuel metering in an internal combustion engine.

In the area of such an injector or such a piezoelectric actuator a variety of errors occur. For example, due to various Causes such as wear and tear, increased mechanical friction occur. This can go so far that individual components of the injector are no longer move. Furthermore, it can occur that leaks occur or that Flows of liquids to be controlled are prevented or made more difficult. Further can occur as an error that individual layers of the piezo actuator are damaged or not are more functional. Furthermore, the case may occur that the actuator is faulty is electrically contacted.

Advantages of the invention

According to the invention, it is provided that a characteristic curve of the actuator is determined and this is compared with an expected characteristic. The determined characteristic deviates from the expected characteristic, an error is recognized according to the invention. With one Procedure can cause numerous errors in the area of the actuator or in the area of the Injector can be reliably recognized.

A force-displacement characteristic is preferably determined. This is with little effort determinable. Certain errors lead to characteristic courses. From these It is possible to reliably identify various errors over the course of the course. The force-displacement characteristic can be done easily by capturing pairs of values for the cargo and the voltage can be determined.

According to the invention, the method and the device are tested as part of the test At regular intervals, for example at Maintenance work and / or carried out continuously while the injector is in operation.

Realizations in the form of a are of particular importance Computer program with program code means and in the form of a Computer program product with program code means. The invention Computer program has program code means to complete all steps of the perform the inventive method when the program on a Computer, in particular a control unit for an internal combustion engine Motor vehicle is running. In this case, the invention is in one Control unit stored program realized so that this with the program provided control unit represents the invention in the same way as the method whose execution the program is suitable. The invention Computer program product has program code means which are based on a computer-readable data carriers are stored by the method according to the invention perform when the program product on a computer, especially a Control unit for an internal combustion engine of a motor vehicle is executed. In this In this case, the invention is implemented by a data carrier, so that the The inventive method can be carried out if the program product or the data carrier in a control unit for an internal combustion engine, in particular one Motor vehicle is integrated. As a data carrier or as a computer program product in particular an electrical storage medium can be used, for example a read-only memory (ROM), an EPROM or an electrical one Permanent storage such as a CD-ROM or DVD.

Advantageous and expedient refinements and developments of the invention are characterized in the subclaims.

drawing

The invention is described below with reference to the drawing Embodiments explained.

Figur 1 ein Blockdiagramm der erfindungsgemäßen Vorrichtung,

Figur 2 ein Flussdiagramm der erfindungsgemäßen Vorrichtung,

Figuren 3 bis 7 verschiedene Kennfelder, die charakteristisch für verschiedene Fehler sind und

Figur 8 ein Injektor.

Show it

FIG. 1 shows a block diagram of the device according to the invention,

FIG. 2 shows a flow diagram of the device according to the invention,

Figures 3 to 7 different maps that are characteristic of different errors and

Figure 8 is an injector.

Description of the embodiments

The procedure according to the invention is described below using the example of a So-called common rail system, in which a piezoelectric actuator by one The injector controls the amount of fuel that is described.

In Figure 1, the essential elements of a device for controlling a Piezo actuator shown. An output stage is labeled 100. This power amp applies voltage to the actuator (not shown) and charges it to one certain time by energizing to predetermined values. Accordingly the actuator by energizing in opposite directions from the output stage to a predetermined one Unload time again. The output stage 100 comprises a current detection 110 and a Voltage detection 120. With these, the current I, which when charging in the Actuator and flows out of the actuator during unloading, measured. Furthermore, the Voltage detection 120 is the voltage U, which characterizes the voltage at the actuator. A corresponding output stage is described for example in EP 11 38 902.

The output signal I of the current detection 110 reaches an integrator 130. Am The output of integrator 130 has signal Q, which characterizes the amount of charge, with which the actuator was charged.

The output signal Q of the integrator and the output signal U der Voltage detection 120 arrive at a map 140. Starting from the Parameters Q and U determine the characteristic diagram determination 140 the current force-displacement characteristic. The force-displacement characteristic curve determined in this way arrives at the map evaluation 150, which it includes compares a given characteristic curve. Detects the map evaluation 150 a corresponding deviation, this is reported back to the output stage 100 or alternatively or additionally displayed to the driver by means of an error display 160. Of it can also be provided that an error of a higher-level control system Influenced fuel metering, for example, is also signaled.

The mode of operation of this device is described below using the flow diagram of Figure 2 described. The method described below is preferred used in the ongoing operation of the internal combustion engine. With all controls one Piezo actuator, or only with a predetermined number of controls that will The method described below is used. Alternatively or in addition, it can also be provided that the procedure during maintenance or before the first start-up of the actuator is carried out. That means the process is both in operation, as well as during maintenance or before or when the actuator is started up for the first time used.

In a first step 200, the rail pressure P is measured at the beginning of the method. This pressure is the pressure against which the actuator works. With The start of the charging process is at fixed intervals or at fixed intervals Crankshaft revolution in a step 210, the voltage U on the actuator, and the Charge Q that is loaded into the actuator is recorded. The subsequent query 220 checks whether the actuator is fully charged. That it is checked whether the loading process is completed. If this is not the case, step 210 takes place again. This means that during the entire charging process in discrete measuring points, which are preferred are equidistant, the charge Q that flows into the actuator and the one applied to the actuator Voltage U is detected.

If the charging process has ended, the force-displacement characteristic is determined in step 230. In the subsequent step 240, the force-displacement characteristic curve determined with a expected course compared. The subsequent query 250 checks whether a There is a deviation. If this is not the case, the program ends in step 260 if this is the case, an error is recognized in step 270. Such a detected error will preferably displayed to the driver or there is a corresponding emergency operation initiated and / or performed an emergency shutdown.

Three phases are usually used to control an actuator during an injection distinguished. In a first phase, the actuator is charged and moves from it first position to a second position, in a second phase the actuator remains charged and remains in its position, in a third phase it is unloaded and taken thus reverting to its original first position.

The described measurement of the charge Q and the voltage U takes place at a preferred embodiment over all three phases. Various mistakes can already be made be recognized at the end of the charging process. Other errors, however, can only after Completion of the second phase and / or detected after the end of the discharge process become.

The force-displacement characteristic is plotted in FIG. The power is with F and the way with X denotes. The force-displacement characteristic of an actuator is for a lower one Rail pressure P1 dashed and a higher rail pressure P2 with a solid line applied. In addition, the lines in this diagram are of constant voltage dashed and the lines of constant charge dotted. With increasing The corresponding lines shift with voltage U or with increasing charge Q. constant voltage and / or constant charge to the right.

Each point of the force-displacement characteristic clearly corresponds to a pair of values consisting of voltage U and charge Q. The value for charge Q and voltage measured in step 210 U each result in a point in the force-displacement characteristic. By measuring several Value pairs for the charge Q and the voltage U during the charging process and / or the force-displacement characteristic curve is determined in step during the unloading process 230th

As long as the force on the actuator due to the rail pressure is greater than that for the Coupler applied actuator force, the control valve remains closed. The control valve is located in its lower seat US. The actuator force only works against the elasticity of the individual elements of the injector. According to what is happening The actuator executes a corresponding stroke without balancing the forces Control valve opens. This causes the force-displacement characteristic to be almost linear History. If the actuator force applied via the coupler is greater than that of Rail pressure applied force, so the sealing element detaches from the sealing seat and the actuator expands. This point is shown in the force-displacement characteristic as separation point A1 or referred to as A2 at increased pressure. Up to this point is the force-displacement characteristic almost linear.

In the following, the actuator continues to expand until there is a balance of forces again between actuator force and the force due to the rail pressure on the control valve. The new balance of forces is formed when the control valve is in the OS point reached the upper seat. Due to the sensory effect of the piezo actuator, one leads greater force on the actuator leads to greater voltage on the actuator. With the same charge you get a higher voltage U with the same stroke X as a result of higher rail pressure.

If the sealing element of the control valve is stuck, the actuator only works against it Elasticity of the injector parts. Such clamping of the sealing element can, for example caused by contamination and / or a mechanical defect his. A corresponding defect has the effect that the separation point is along of the straight line drawn in dash-dot lines in FIG.

With a control valve jammed in the closed seat, this results in comparison to Faultless operation with the same charge a higher voltage U, since the actuator only works against the elasticity of the injector parts and realizes a smaller expansion, than in error-free operation. This allows a simple measurement on a few Detect operating points a corresponding defect. According to the invention sticking valve detected when a combination of voltage and charge values occurs that lies on the straight line shown and not with the measured rail pressure is plausible, i.e. at a pressure P1 an error is detected when the measuring pressure at correspondingly larger voltages and / or charges.

According to the invention, in step 240, a jamming valve is identified checks whether the straight line exceeds the permissible separation point, which depends on the rail pressure, goes out, or it is checked whether a corresponding control Characteristic point, i.e. a pair of values for the voltage and the charge, above the expected separation point occurs.

Another mistake is that the hydraulic coupler between the Actuating piston of the actuator and the piston of the control valve between two meterings is only filled incompletely. Such an incompletely filled hydraulic coupler has the consequence that the distance between the actuating piston of the actuator and the piston of the control valve is smaller than that of a fully filled hydraulic coupler. As a result, the actuator has the shorter distance with a larger stroke compensate. The cause of an unfilled coupler are, for example, a too low filling pressure, or that the control valve remains open and not closes.

In the case of an incompletely filled coupler, compared to the error-free one Operation an offset to the right on the stroke axis X, since the piezo actuator is a so-called Makes empty travel before a corresponding actuator force builds up. This causes in the Force-displacement curve an area in which the slope of the force-displacement curve is clear is smaller than expected. The slope preferably takes a value of almost zero on. A corresponding course is shown by dash-dotted lines in FIG. 4 as an example. If a corresponding characteristic curve curve is recognized in step 240, the curve recognizes Setup on an insufficiently filled coupler.

The detection takes place, for example, in that a smaller one with the same charge Voltage is present or that, in order to achieve the same voltage, more charge in the Actor must be invited. The gradient of the force-displacement characteristic is preferred determined and detected for errors when the slope is almost zero assumes that is less than a certain value. The certain value corresponds the slope in perfect condition.

If individual layers of the piezo ceramic of the piezo actuator fail, the result is a changed course of the straight line with constant charge or the straight line with constant voltage. These changed straight lines with constant charge and / or Voltage are shown in Figure 5. Such failures of actuator layers are in the Essentially due to cracks in the layer or drop in the contacting electrode caused. The straight lines of constant tension are steeper with constant ones Force axis section, since more tension is required to achieve the same stroke as in to realize flawless case. The straight lines of constant charge are steeper constant expansion, since there are fewer layers for charge absorption. This leads to the consumption of the force-displacement characteristic. In the event of a shift failure compared to fault-free operation with the same charge, a higher one Actuator voltage, since the piezo actuator requires more voltage to achieve the same stroke realize. For this purpose, the expected course of the force-displacement characteristic with the determined characteristic curve compared. Based on the determined deviations then the error is recognized.

The likelihood that a shift failure immediately after installation on Band end at the customer is very low. Because of this, the same can be done Procedure a polarity reversed actuator can be recognized. Reverse polarity of the actuator leads to a re-polarization of the ceramic, which in turn leads to a lower capacity of the Actuator.

If a shift failure is detected, an entry is made in the error memory of the control unit and / or the error is signaled to the driver and causes him to service visit. As a rule, a larger shift loss means that through the Control valve in the associated cylinder no fuel is injected.

If there is an error, there is increased friction in the knitting chain between Actuator and control valve, so a higher actuator force is used to overcome the frictional force needed. This manifests itself in the fact that compared to faultless operation with the same Charge a higher actuator voltage is required because the actuator is also against the additional frictional force works and realizes a smaller stroke.

If the friction and the stroke loss become too great, the control valve will not open more and there is no injection.

With an additional frictional force, the result is in comparison to faultless operation same charge, a lower actuator voltage when charging, because the piezo actuator is additional works against the additional friction and follows with a larger expansion. In an extreme case, the control valve would no longer close and would therefore become Continuous injection and possibly unwanted acceleration of the vehicle come.

If one looks at the loading and unloading process, the result is in comparison to faultless operation of the injector with the same charge, a larger voltage hysteresis, which is also expressed in a larger electrical power loss of the piezo actuator. In Figure 6 is a corresponding displacement-force diagram of an actuator with increased frictional force applied. When charging, the force increases significantly steeper than on one faultless actuator. That means the slope of the force-displacement characteristic is greater than one expected value. This error is recognized if the slope of the Force-displacement characteristic exceeds a certain value. The certain value corresponds the slope when in perfect condition.

If an impermissibly high frictional force is recognized, an entry is preferably made in the Control unit fault memory. Signaling to the driver can also be carried out by a signal lamp and / or other measures, such as torque limitation, respectively. This can prevent a total failure of the injector in good time. That it can be timely due to the possibly increasing friction force long-term injections or misfires can be avoided in good time. By reducing the available torque, the driver forced to go to a workshop. With a slightly increased friction within permissible limits it can be provided that the changed opening and Injector closing behavior by correcting the electrical activation starts and / or the electrical activation duration and / or the charging time and / or the Actuator target voltage is corrected.

The characteristic curve which results in the case of a leaky coupler is plotted in FIG. is If the coupler leaks, this means that the actuator will also leak when the charge is constant continues to move and the stroke increases until it regains its balance of forces comes. In the force-displacement characteristic of the actuator, this means that at constant permanent charge the actuator voltage along the straight line for constant charge sinks. The temporal change in the actuator voltage depends on the size of the Leakage. As the actuator stroke continues to increase, however, the actuator force also decreases until the force due to rail pressure increases and the sealing element extends to the equilibrium of forces moved back. This closes the nozzle needle again. According to the invention it was recognized that in the case of a leaky coupler compared to the faultless case a falling actuator voltage at the working point results in an open seat. With a recognized leaky coupler, an entry is made in the fault memory of the control unit. Furthermore, signals the error to the driver so that he can have the error rectified. This is provided that the characteristic curve over the entire injection, that is over the Charging and unloading is detected.

8 shows a schematic illustration of an injector 1 with a central one Drilling. In the upper part is an actuating piston 3 with a piezoelectric actuator 2 in the introduced central bore, the actuating piston 3 is firmly connected to the actuator 2 is. The actuating piston 3 closes off a hydraulic coupler 4 while downward an opening with a connecting channel to a first seat 6 is provided is in which a piston 5 is arranged with a valve closing member 12. The Valve closing member 12 is designed as a double closing control valve. It closes the first seat 6 when the actuator 2 is at rest. When actuating actuator 2, the means when a control voltage Ua is applied to terminals +, -, the actuator actuates 2 the actuating piston 3 and presses the piston 5 with the hydraulic coupler 4 Closure member 12 in the direction of a second seat 7. Below the second seat In a corresponding channel, a nozzle needle 11 is arranged, which the outlet in one High-pressure duct (common rail pressure) 13 closes or opens, depending on which one Control voltage Ua is present. The high pressure is caused by the medium to be injected, for example fuel for an internal combustion engine, supplied via an inlet 9, The inflow amount of the medium is via an inlet throttle 8 and an outlet throttle 10 controlled in the direction of the nozzle needle 11 and the hydraulic coupler 4. The Hydraulic coupler 4 has the task, on the one hand, of increasing the stroke of the piston 5 amplify and on the other hand the control valve from the static temperature expansion of the Decouple actuator 2. The refilling of the coupler 4 is not shown here.

The mode of operation of this injector is explained in more detail below. With everyone Actuator 2 is actuated by actuating piston 3 in the direction of the hydraulic coupler 4 moves. The piston 5 with the closing member 12 also moves in the direction towards the second seat 7. Part of the hydraulic Coupler 4 sensitive medium, such as the fuel, pressed out.

The hydraulic coupler 4 must therefore be refilled between two injections to maintain its functional reliability.

A high pressure prevails over the inlet channel 9, that in the common rail system for example, can be between 200 and 2000 bar. This pressure works against the Nozzle needle 11 and keeps it closed so that no fuel can escape. Now due to the control voltage Ua, the actuator 2 is actuated and thus the closure member 12 is moved in the direction of the second seat, the pressure in the high pressure area decreases and the nozzle needle 11 releases the injection channel. With P1 is the so-called Coupler pressure denotes how it is measured in the hydraulic coupler 4. In the coupler sets a stationary pressure P1 without control Ua, which is 1/10 of the Pressure in the high pressure part. After the actuator 2 has been discharged, the coupler pressure is P1 approximately 0 and is raised again by refilling.

According to the invention, in the course of the control of an injector in fixed Periods of time or at fixed angular intervals pairs of measured values for the voltage on the Injector is present, and the charge that is loaded into the injector is detected. The The charge is detected by a current measurement, the current value is integrated. These pairs of values are entered in a map in the control unit. This map determined in this way is then compared with an expected map. If the measured map deviates from the expected map, an error occurs recognized. Different errors are identified based on the type of deviation.

The map in which the expected course of the force-displacement characteristic is stored is preferably before the first start-up and / or the first start-up of the Injector determined. It is particularly advantageous if this reference map is applied stored and learned during operation. This means whenever that Map is measured again, the map values with the old map compared. If the deviation is smaller than a threshold value, the old and new values a new mean is determined. Alternatively, it can also be provided that that if there is a small deviation, the new value is used immediately. give way the old and the new value pairs differ significantly from each other, i.e. by more than one Threshold, so it is recognized for errors.

Claims (12)

Method for monitoring a piezoelectric actuator for controlling a Injector, wherein a characteristic curve of the actuator is determined, the characteristic curve determined is compared with an expected characteristic curve and if the a characteristic of the injector was identified from the expected characteristic becomes. A method according to claim 1, characterized in that charge values and associated voltage values are recorded during a charging process and / or an unloading process. Method according to claim 2, characterized in that a force-displacement characteristic is determined on the basis of the charge values and assigned voltage values. Method according to one of the preceding claims, characterized in that a mechanical blockage is detected when the force-displacement characteristic has a largely linear course. Method according to one of the preceding claims, characterized in that an incompletely filled coupler is detected when the force-displacement characteristic curve does not rise linearly at the beginning of the charging process. Method according to one of the preceding claims, characterized in that a leaky coupler is detected when the force-displacement characteristic curve drops at the end of the charging process. Method according to one of the preceding claims, characterized in that an increased internal friction is detected when the force-displacement characteristic increases more than expected. Method according to one of the preceding claims, characterized in that a layer failure and / or polarity reversal is detected when the force-displacement characteristic curve has been consumed. Device for monitoring a piezoelectric actuator for controlling a Injector, with means that determine a characteristic curve of the actuator, the determined Compare the characteristic curve with an expected characteristic curve and if there is a deviation an error of the injector in the determined characteristic from the expected characteristic detect. Computer program with program code means to do all the steps of everyone perform any of claims 1 to 11 when the program is on a Computers, in particular a control device for an internal combustion engine, is performed. Computer program product with program code means based on a Computer readable disks are saved to the procedure after each perform any of claims 1 to 11 when the program product is on a computer, in particular a control device for an internal combustion engine, is performed. Digital storage medium, in particular floppy disk, with electronically readable Control signals so with a programmable computer system can cooperate that a method according to one of claims 1 to 11 is performed.

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