EP1697633B1 - Method for diagnosis in a fuel injection device comprising a piezoactuator - Google Patents

Description

State of the art

The invention initially relates to a method for the diagnosis of a fuel injection device, which has a piezoelectric actuator for actuating a valve element.

In particular, in internal combustion engines with direct fuel injection fuel injectors are used whose valve elements are not actuated electromagnetically, but at least indirectly by the change in length of a piezoelectric actuator. The advantage of piezo actuators lies in their very short switching time and the possible very precise stroke adjustment. By using such fuel injectors, the fuel can be very accurately introduced into the combustion chambers of the internal combustion engine, which in turn has a favorable emission behavior and low fuel consumption.

For the operation of the internal combustion engine, the correct function of the piezoelectric actuator therefore plays a central role, and this in turn makes it necessary to monitor the correct functioning of the piezoelectric actuator. For example, during operation of the internal combustion engine, the capacity is known to determine the used piezo actuators again and again. If a large change in capacity is detected within a certain period of time, this is an indication, for example, of damage to the piezoactuator. In this case, the fuel can no longer be introduced into the combustion chamber of the internal combustion engine with the required accuracy by the corresponding fuel injection device.

Also detected is when a fuel injector is blocked in the open position. In such a case, a forced shutdown of the internal combustion engine may even be necessary. If a malfunction is detected, an error entry is made in a fault memory. The stored error data can be read in a workshop by a corresponding diagnostic device. As a result, the installer receives information about the location and the type of error that has occurred.

DE 198 45 042 A1 describes a method and an arrangement for the diagnosis of a capacitive actuator. The corresponding control unit is integrated in an engine control unit. WO 99/67527 A2 describes a method and an arrangement for controlling a capacitive actuator. Again, the corresponding control unit is part of an engine control unit. EP 1 139 448 A1 describes a method and a device for controlling the drive voltage of a piezoelectric actuator. EP 1 138 907 A1 discloses a fuel injection system.

Object of the present invention is to develop a method of the type mentioned so that the diagnosis of the fuel injection device in the "field", that is far away from a workshop or a appropriately equipped workshop vehicle, is possible.

This task is solved according to the claims.

Advantages of the invention

Characterized in that the device comprises a separate from a control and regulating device of the fuel injection device, portable diagnostic device which forms a closed unit and at least one optical or acoustic display for displaying the functional state of the piezoelectric actuator, a diagnosis "in the field" allows , which can be done independently of a complex engine tester and also independent of the engine control unit. The diagnostic device according to the invention can be so small that it can be carried for example on board a breakdown service vehicle. The fact that the device forms a self-contained unit means that the power supply, the signal conditioning, the optical or acoustic display, and an evaluation circuit are arranged within a compact housing. This facilitates the handling again.

The diagnostic device may have a capacitor charging circuit which provides the energy required to drive the piezoelectric actuator.

To control piezo actuators high voltages and comparatively high currents are necessary. Since no continuous repeated activation of the piezoelectric actuator is required for a state diagnosis of the piezoactuator, but a single actuation within a certain period is sufficient, a capacitor charging circuit offers a simple, space-saving and inexpensive Possibility to provide the energy required to drive the piezoelectric actuator. The energy for charging the capacitor of the capacitor charging circuit can be provided in the case of a motor vehicle, for example, from the 12 V car battery, from a 230 V power supply, or, for example, from a photovoltaic system.

It is particularly advantageous if the capacitor charging circuit is a commercially available circuit, as used for flash units or the like. In this case, the device is particularly inexpensive.

The use of the device according to the invention is facilitated by the fact that it comprises a connecting device, which is complementary to a connecting device to the fuel injection device or the internal combustion engine. To use the device according to the invention then it is sufficient, for example, to deduct a vehicle-side connector from the Kraftstoff-Einspritzvorrichtüng and instead to connect a plug of the diagnostic device according to the invention with the fuel injection device.

It is also proposed that the device has an interface for connecting a PC. In this way, if necessary, further automated tests can be carried out by means of the device according to the invention, which are programmed on the PC. The evaluation of the diagnosis result can be done in this way even more differentiated. As a PC, a notebook or tablet PC is advantageously used.

In the method according to the invention, an error memory does not have to be accessed. Instead, in the Standstill of the internal combustion engine, the fuel injection device directly connected to a corresponding diagnostic device, which tries to introduce a certain and predetermined amount of charge in the piezoelectric actuator. From the actually introduced amount of charge can then be determined in a simple manner, the actual capacity of the piezoelectric actuator. This is a measure of the current functional state of the piezoelectric actuator. The charge is determined, for example, on the basis of the actual current flow.

In knowledge of the current capacity of the piezoelectric actuator so it can be easily found out whether the piezoelectric actuator for a fault that occurred may be the cause or not. In this case, the piezoelectric actuator for the condition test does not have to be removed from the internal combustion engine, which shortens the time required to carry out the diagnosis.

Since, as I said, no data exchange takes place but only current characteristic electrical values of the piezoelectric actuator are tested, the diagnostic device can be very simple and small build, so that it can be anywhere, even outside a workshop or without consulting a workshop car, used. If necessary, it is conceivable to integrate such a diagnostic device into the vehicle tool, which is present anyway, in a motor vehicle. In addition, with such a method, an input check may also be performed before installing a fuel injection device in an internal combustion engine.

It is also proposed that the diagnostic device determines a course of the capacity. The course of the capacity is even more meaningful with regard to a known course of the applied voltage and the applied current the functional state of the piezoelectric actuator as a single absolute value of the capacity. The functionality of the piezoelectric actuator can be determined even better in this way.

It is also advantageous if the diagnostic device compares the ascertained capacitance or the determined course of the capacitance with at least one reference capacitance or a reference curve and generates a signal depending on the result of the comparison. In this development, the interpretation of the result is removed from the user. By comparison, the diagnostic device provides the same diagnostic result.

In a further development, it is proposed that a display with at least two colors is actuated on the basis of the signal, which indicates whether the determined capacitance or the course lies within a tolerance range around the reference capacitance or the reference characteristic. In the simplest case, when two colors are used, the diagnostic device gives an easily recognizable visual indication as to whether the piezoactuator or fuel injector investigated is in order or if there is a fault. The handling of the method according to the invention is simplified in this way and accelerates the diagnosis.

It is particularly advantageous if the applied voltage during the diagnosis corresponds at least approximately to a course which occurs during normal operation of the fuel injection device. A typical example of this is that the diagnostic device applies a voltage to the piezoelectric actuator with a linearly increasing, a constant, and a linear sloping section applies. In this case, the diagnostic device, despite stationary internal combustion engine, simulates a real operating situation. The diagnostic result is particularly meaningful in this case.

drawing

Figur 1

eine schematische Darstellung einer Brennkraftmaschine mit einer Kraftstoff-Einspritzvorrichtung mit einem Piezoaktor, und eines Diagnosegeräts;

Figur 2

ein Diagramm, in dem eine Spannung und ein Strom, die an den Piezoaktor von Figur angelegt werden, über der Zeit aufgetragen sind; und

Figur 3

ein vereinfachtes und schematisches elektrisches Schaltbild des Diagnosegeräts von Figur 1.

Hereinafter, a particularly preferred embodiment of the present invention will be explained in detail with reference to the accompanying drawings. In the drawing show:

FIG. 1

a schematic representation of an internal combustion engine having a fuel injection device with a piezoelectric actuator, and a diagnostic device;

FIG. 2

a graph in which a voltage and a current, which are applied to the piezoelectric actuator of Figure, plotted against time; and

FIG. 3

a simplified and schematic electrical diagram of the diagnostic device of FIG. 1 ,

Description of the embodiment

In FIG. 1 an internal combustion engine carries a total of the reference numeral 10. It is used to drive a motor vehicle, which in FIG. 1 , as well as the internal combustion engine 10, is indicated only by a dash-dotted line and which carries the reference numeral 12. To the internal combustion engine 10 includes a fuel system 14. This includes a fuel tank 16 from which a conveyor 18 promotes the fuel to a fuel rail 20. This is also called "rail", and in it the fuel is stored under high pressure.

To the fuel manifold 20 a plurality of fuel injectors 22 are connected. These inject the fuel directly into each one assigned to them Combustion chamber 24 a. For purposes of illustration, only one fuel injector 22 and one combustion chamber 24 are shown. The fuel injection device 22 comprises a valve element, not visible in the figure, which, depending on the position, releases fuel outlet openings (not shown) through which the fuel can pass from the fuel injection device 22 into the combustion chamber 24. The position of the valve element is influenced by the current length of a piezoelectric actuator 26. This changes depending on the charge that is placed in it. For this purpose, the piezoelectric actuator 26 via a fuel injector 22 mounted bushing 27 and a connector 29 is connected to a control and regulating device 28.

For the operation of the internal combustion engine 10, a correct function of the piezoelectric actuator 26 is of central importance. Only when the piezoelectric actuator 26 is operating correctly is the fuel injection device 22 injecting the desired amount of fuel into the combustion chamber 24. The emission behavior and the fuel consumption of the internal combustion engine 10 therefore also depend on the correct function of the piezoelectric actuator 26.

The function of the piezoelectric actuator 26 is repeatedly monitored during operation of the internal combustion engine 10 by the control and regulating device 28. In the case of an error occurs an entry in a fault memory of the control and regulating device 28 and / or the internal combustion engine 10 is switched to an emergency operation or even completely shut down. The entries in the fault memory can be read, for example, in a workshop or by a mobile service vehicle by a diagnostic device which is connected to the control and regulating device 28. However, such a diagnostic device is big and heavy and therefore difficult to transport. In addition, it is relatively expensive due to the expensive electronics.

In order to be able to carry out a state diagnosis of the fuel injection device 22 and in particular of the piezoelectric actuator 26 on the way, far away from a workshop or a service vehicle, the fuel injection device 22 has a socket 30 connected directly to the piezoelectric actuator 26, into which a plug 32 a small, portable diagnostic device 34 can be inserted. The plug 32 is connected to the diagnostic device 34 via a cable 36. In a not shown. Embodiment is dispensed with the separate socket 30. Instead, the plug 29, with which the control and regulating device 28 is connected to the socket 27, pulled out of this and the plug 32 of the diagnostic device 34 instead plugged into the socket 27.

To diagnose the piezoelectric actuator 26, a current I is applied to the piezoelectric actuator 26 by the diagnostic device 34 and the voltage U resulting at the capacitor is determined. The corresponding to the curve U is in FIG. 2 shown. It can be seen that the voltage U applied to the piezoactuator 26 normally has first a linearly rising section, then a section with constant voltage, and finally a section descending linearly. This corresponds approximately to the ramp-shaped actuation of the piezoelectric actuator 26 during normal operation of the internal combustion engine 10. The maximum voltage level reached as well as the steepness of the flanks corresponds at least approximately to a customary activation of the piezoactuator 26 during an injection process.

During the rise of the voltage U, a constant current I (dashed line in FIG FIG. 2 ). Due to the rising voltage U, a change in length of the piezoelectric actuator 26 is effected, which would lead to an injection of fuel during operation of the internal combustion engine 10. In order to prevent damage by the diagnosis of the internal combustion engine 10, the diagnosis is therefore carried out only when the internal combustion engine 10 is stopped. In the diagnostic device 34, the integral of the current I flow over the time t is calculated. This integral corresponds to the charge Q which has been introduced into the piezoelectric actuator 26. If the charge Q is divided by the voltage U, the capacitance C of the piezoactuator 26 is obtained.

The capacitance C of the piezoelectric actuator 26 is an important parameter for the functional state of the piezoelectric actuator 26. If, for example, a fracture of the piezoactuator 26 occurs, this results in a significant change in the capacitance C. This can be detected by the use of the diagnostic device 34. In the simplest case, the determined capacitance C is output as a numerical value from the diagnostic device 34. The user can then judge from the numerical value himself whether the piezoelectric actuator 26 is OK or not. But it is also possible that the diagnostic device automatically compares the detected capacity with an upper and a lower limit in a corresponding evaluation circuit.

If the determined capacitance C lies in the range between the two limit values, a green lamp 38 lights up on the diagnostic device 34. This signals that the piezoactuator 26 is in order. If the determined capacitance C is close to one of the limit values, a yellow lamp 40 lights up on the diagnostic device 34, which signals that the piezoactuator 26 does not exist seems to be completely defective, but apparently he no longer fully meets the specification. By contrast, if the capacitance C is clearly outside the range defined by the two limit values, a red lamp 42 lights up on the diagnostic device 34, which indicates to the user that the piezoactuator 26 is defective.

How out FIG. 3 As can be seen, the diagnostic device 34 builds very simply because a commercially available capacitor charging circuit 44 is used to provide the supply voltage and the supply current that are applied to the piezoelectric actuator 26 for diagnosis. For example, it is possible to use an LT3420 capacitor charging circuit (Linear Technology Magazine, May 2002) commonly used to provide the firing energy for xenon flashes of cameras and having a capacitor with a capacitance of 220 μF, which is within 3 , 5 s with a 5 V input voltage of 50 V to 320 V can be loaded.

However, in the present diagnostic apparatus 34, unlike a flash unit of a photographic apparatus, the piezo actuator 26 is not only required to be charged but also discharged again FIG. 3 shown electrical circuit of the diagnostic device 34 not only via a triggered charging signal 46, but also via a discharge circuit 48 for constant current. The control of the charging or discharging process via an opteration amplifier 50 and two Schmitt trigger 52 and 54. In order to control the flow of the diagnosis in the diagnostic device 34, in this a microprocessor with an A / D converter is integrated. For the connection to a PC, in particular a note book, the diagnostic device 34 also has a corresponding interface 56 (cf. FIG. 1 ).

In the FIG. 3 shown circuit is powered via the terminals 58th. Possible here is a built-in battery, batteries, a connection to an electrical system of the motor vehicle 12, a connection to a 230 V mains voltage, or a supply via a photovoltaic converter. A DC / DC converter 60 connected to the terminals 58 provides the power for boost circuits or, for example, the indicators 38-42.

In the in the FIGS. 1 to 3 described embodiment, a diagnostic device 34 has been shown, which is used for the diagnosis of a built in a motor vehicle 12 fuel injection device 22. Basically, the proposed method and the proposed diagnostic device 34.aber also be used in the motor vehicle manufacturer for receiving the supplied fuel injectors 22, even before they are installed in the internal combustion engine 10 and the motor vehicle 12. In this way it can be avoided that defective fuel injection devices 22 are installed in an internal combustion engine 10 or a motor vehicle 12.

The diagnostic device 34 is very compact and can therefore be part of an on-board tool of the motor vehicle 12. It comprises in a common housing, the power supply, all transducers, an evaluation circuit, a control and a display processor, and the displays 38 to 42, or alternatively or additionally an LCD display, and the connecting cable 36 and the plug 32nd

Claims (9)

1. Device (34) for diagnosing a fuel injection device (22) with a piezo-actuator (26), which device determines a charge (Q) applied to the piezo-actuator (26) and a capacitance (C) of the piezo-actuator (26) on the basis thereof, characterized in that said device comprises a transportable diagnostic unit (34) which is separate from an open-loop and closed-loop control apparatus (28) of the fuel injection device (22) and which forms an enclosed structural unit and comprises at least one visual display or acoustic indicator (38-42) for indicating the functional state of the piezo-actuator (26).
2. Device (34) according to Claim 1, characterized in that the capacitor charging circuit is a commercially available circuit (44) such as is used for flash units or the like.
3. Device (34) according to one of Claims 1 to 2, characterized in that it comprises a connecting apparatus (32) which is complementary to a connecting apparatus (30) on the fuel injection device (22).
4. Device (34) according to one of the preceding claims, characterized in that said device (34) has an interface (56) for connecting a PC.
5. Method for operating a device according to one of the preceding claims, characterized in that the fuel injection device (22) is connected directly to the diagnostic unit (34), in that a specific voltage (U) is applied to the piezo-actuator (26) via the diagnostic unit (34), and in that the charge (Q) which is applied to the piezo-actuator (26) is determined by the diagnostic unit (34) and a capacitance (C) of the piezo-actuator (26) is determined therefrom.
6. Method according to Claim 5, characterized in that the diagnostic unit (34) determines a profile of the capacitance (C).
7. Method according to one of Claims 5 or 6, characterized in that the diagnostic unit (34) compares the determined capacitance (C) or the determined profile of the capacitance with at least one reference capacitance or a reference profile and generates a signal as a function of the result of the comparison.
8. Method according to Claim 7, characterized in that on the basis of the signal a visual display (38, 40, 42) with at least two colours is actuated, by means of which it is indicated whether the determined capacitance (C) or the profile is within a tolerance range around the reference capacitance or the reference profile.
9. Method according to one of Claims 5 to 8, characterized in that the applied voltage (U) corresponds, during the diagnosis, at least approximately to such a voltage (U) which occurs during the normal operation of the fuel injection device (22).

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