EP1697633A1

EP1697633A1 - Method for diagnosis in a fuel injection device comprising a piezoactuator

Info

Publication number: EP1697633A1
Application number: EP04762625A
Authority: EP
Inventors: Ulrich Schoor; Kai Sutter
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2003-10-24
Filing date: 2004-08-07
Publication date: 2006-09-06
Anticipated expiration: 2024-08-07
Also published as: CN1871429A; ES2538707T3; WO2005045234A1; US7467543B2; JP2006522574A; EP1697633B1; DE10349824A1; US20070001545A1

Abstract

The invention relates to a method, for diagnosis in a fuel injection device (22), comprising a piezoactuator (26), by means of which a valve element is operated. According to the invention, the fuel injection device (22) is connected to a diagnosis unit (34), a specific voltage is then applied to the piezoactuator (26), by the diagnosis unit (34) and the charge introduced into the piezoactuator (26), by the diagnosis unit (34) and hence a capacitance for the piezoactuator (26), are determined.

Description

Method for diagnosing a fuel injector which has a piezo actuator

State of the art

The invention initially relates to a method for diagnosing a fuel injection device which has a piezo actuator for actuating a valve element.

In particular in internal combustion engines with direct fuel injection, fuel injection devices are used, the valve elements of which are not actuated electromagnetically, but at least indirectly by changing the length of a piezo actuator. The advantage of piezo actuators is their very short switching times and the possible very precise stroke setting. By using such fuel injection devices, the fuel can be introduced very precisely into the combustion chambers of the internal combustion engine, which in turn results in favorable emission behavior and low fuel consumption.

The correct functioning of the piezo actuator therefore plays a central role for the function of the internal combustion engine. and this in turn makes it necessary to monitor the correct functioning of the piezo actuator. For example, the capacity is known during the operation of the internal combustion engine to determine the piezo actuators used again and again. Is a strong modifier Derun ^'capacity within a certain period determined this is an indication example of harm to the piezoelectric actuator. 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. It is also detected when a fuel injection device is blocked in the open position. In such a case, it may even be necessary to shut down the internal combustion engine. If a malfunction is detected, an error is entered in an error memory. The stored error data can be read out by a corresponding diagnostic device in a workshop. This gives the fitter information about the location and type of fault that has occurred.

The object of the present invention is to develop a method of the type mentioned at the outset so that the fuel injector can also be diagnosed in the "field", that is to say far from a workshop or a suitably equipped workshop vehicle.

This object is achieved in a method of the type mentioned at the outset in that the fuel injection device is connected directly to a diagnostic device that is connected to the diagnostic device

A specific voltage is applied to the piezo actuator and that the charge introduced into the piezo actuator and a capacitance of the piezo actuator are determined by the diagnostic device. Advantages of the invention

In the method according to the invention, an error memory does not have to be accessed. Instead, when the internal combustion engine is at a standstill, the fuel injection device is connected directly to a corresponding diagnostic device which attempts to introduce a specific and predetermined amount of charge into the piezo actuator. The actual capacitance of the piezo actuator can then be determined in a simple manner from the amount of charge actually introduced. This is a measure of the current functional state of the piezo actuator. The charge is determined, for example, on the basis of the current actually flowing.

Knowing the current capacity of the piezo actuator, it is therefore easy to determine whether the piezo actuator can be the cause of a malfunction that has occurred or not. The piezo actuator for the condition check does not have to be removed from the internal combustion engine, which shortens the time for carrying out the diagnosis.

Since, as I said, no data exchange takes place but only current characteristic electrical values of the piezo actuator are checked, the diagnostic device can be made very simple and small, so that it can be used anywhere, even outside a workshop or without using a workshop trolley. If necessary, it is conceivable to integrate such a diagnostic device in the vehicle tool, which is already present, in a motor vehicle. In addition, such a method can also be used to carry out an incoming inspection prior to the installation of a fuel injection device in an internal combustion engine. ^' Advantageous developments of the invention are specified in the subclaims.

First, it is proposed that the diagnostic device determine a course of the capacity. The course of the capacitance is even more meaningful with a known course of the applied voltage and the applied current with regard to the functional state of the piezo actuator than a single absolute value of the capacitance. The functionality of the piezo actuator can be determined even better in this way.

It is also advantageous if the diagnostic device compares the determined capacity or the determined course of the capacity with at least one reference capacity or a reference course and generates a signal depending on the result of the comparison. In this development, the interpretation of the result is relieved of the user. Through the comparison, the diagnostic device immediately provides the diagnostic result.

In a further development, it is proposed that on the basis of the signal, a display with at least two colors is activated, by means of which it is indicated whether the determined capacity or the course lies within a tolerance range around the reference capacity or the reference course. In the simplest case, if two colors are used, the diagnostic device gives an easily recognizable visual indication as to whether the piezo actuator under investigation or the fuel injection device under investigation is OK or whether there is an error. The handling of the method according to the invention is simplified in this way and the diagnosis is accelerated. It is particularly advantageous if the voltage applied 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 piezo actuator with a linearly increasing, a constant, and a linearly decreasing section. In this case, the diagnostic device simulates a real operating situation despite the stationary internal combustion engine. The diagnostic result is particularly meaningful in this case.

The invention also relates to a device for carrying out the above-mentioned diagnostic method. So that this device is as small as possible and can be manufactured inexpensively, it is proposed that it have a capacitor charging circuit which provides the energy required to control the piezo actuator.

High voltages and comparatively high currents are required to control piezo actuators. Since a continuous diagnosis of the piezo actuator is not required for a state diagnosis of the piezo actuator, but a single activation within a certain period of time is sufficient, a capacitor charging circuit offers a simple, space-saving and inexpensive way to provide the energy required for controlling the piezo actuator. The energy for charging the capacitor of the capacitor Ladeschaltuhg may be provided in the case of a motor vehicle, for example, from ^'the 12 V car battery, by 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 such as that used for flash units or the like. In this case, the device is particularly inexpensive.

It is again particularly advantageous if the device forms a closed structural unit. This means that the power supply, the signal processing, the optical or acoustic display, and an evaluation circuit are arranged within a compact housing. This makes handling even easier. The use of the device according to the invention is facilitated in that it comprises a connecting device which is complementary to a connecting device on the fuel injection device or the internal combustion engine. To use the device according to the invention, it is then sufficient, for example, to pull a vehicle-side connector from the fuel injection device and instead to connect a connector of the diagnostic device according to the invention to the fuel injection device.

It is also proposed that the device have an interface for connecting a PC. As a result, if necessary, further automated tests can be carried out using the device according to the invention, which are programmed on the PC. The evaluation of the diagnostic result can also be carried out in a more differentiated manner in this way. A notebook or tablet PC is advantageously used as the PC.

drawing A particularly preferred exemplary embodiment of the present invention is explained in detail below with reference to the accompanying drawing. The drawing shows:

Figure 1 is a schematic representation of an internal combustion engine with a fuel injection device with a piezo actuator, and a diagnostic device;

Figure 2 is a graph plotting voltage and current applied to the Figure piezo actuator over time; and

FIG. 3 shows a simplified and schematic electrical circuit diagram of the diagnostic device from FIG. 1.

Description of the embodiment

In FIG. 1, an internal combustion engine bears the overall reference number 10. It serves to drive a motor vehicle which, like the internal combustion engine 10, is only indicated by a dash-dotted line in FIG. 1 and which bears the reference number 12. The internal combustion engine 10 includes a fuel system 14. This includes a fuel tank 16, from which a delivery device 18 delivers the fuel to a fuel manifold 20. This is also known as a "rail" and it stores the fuel under high pressure.

A plurality of fuel injection devices 22 are connected to the fuel rail 20. These inject the fuel directly into one of them Combustion chamber 24 a. For reasons of illustration, only one fuel injection device 22 and one combustion chamber 24 are shown. The fuel injection device 22 comprises a valve element, which is not visible in the figure and which, depending on the position, releases fuel outlet openings (not shown) through which the fuel from the fuel injection device 22 can get into the combustion chamber 24. The position of the valve element is influenced by the current length of a piezo actuator 26. This changes depending on the charge that is placed in it. For this purpose, the piezo actuator 26 is connected to a control and regulating device 28 via a socket 27 attached to the fuel injection device 22 and a plug 29.

Correct functioning of the piezo actuator 26 is of central importance for the operation of the internal combustion engine 10. The fuel injector 22 only injects the desired amount of fuel into the combustion chamber 24 if the piezo actuator 26 is working correctly. The

Emission behavior and the fuel consumption of the internal combustion engine 10 therefore also depend on the correct function of the piezo actuator 26.

The function of the piezo actuator 26 is continuously monitored by the control and regulating device 28 during the operation of the internal combustion engine 10. In the event of a fault, an entry is made in a fault memory of the control and regulating device 28 and / or the internal combustion engine 10 is switched over to emergency operation or even completely shut down. The entries in the fault memory can be read out, for example, in a workshop or from 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 more elaborate due to the. Electronics comparatively expensive. In order to be able to carry out a status diagnosis of the fuel injection device 22 and in particular of the piezo actuator 26 also on the way, far away from a workshop or a service vehicle, the fuel injection device 22 has a socket 30 which is connected directly to the piezo actuator 26 and into which a plug is inserted 32 of a small, portable diagnostic device 34 can be inserted. The plug 32 is connected to the diagnostic device 34 via a cable 36. In an exemplary embodiment not shown, the separate bushing 30 is dispensed with. Instead, the plug 29, with which the control and regulating device 28 is connected to the socket 27, is pulled out of the latter and the plug 32 of the diagnostic device 34 is instead inserted into the socket 27. To diagnose the piezo actuator 26, a current I is applied by the diagnostic device 34 to the piezo actuator 26 and the voltage U resulting at the capacitor is determined. That corresponding to curve U is shown in FIG. 2. It can be seen that the voltage U applied to the piezo actuator 26 normally has a linearly increasing section, then a section with constant voltage, and finally a linearly decreasing section. This corresponds approximately to the ramp-shaped activation of the piezo actuator 26 during normal operation of the internal combustion engine 10. The maximum voltage level reached and the steepness of the flanks also correspond at least approximately to a conventional activation of the piezo actuator 26 during an 'injection process. A constant current I flows as the voltage U rises (broken line in FIG. 2). The rising voltage ü causes a change in length of the piezo actuator 26, which would lead to an injection of fuel during operation of the internal combustion engine 10. In order to keep damage caused by the diagnosis away from the internal combustion engine 10, the diagnosis is therefore only carried out when the internal combustion engine 10 is at a standstill. In the diagnostic device 34, the integral of the flowed current I is calculated over the time t. This integral corresponds to the charge Q that was introduced into the piezo actuator 26. If the charge Q is divided by the voltage U, the capacitance C of the piezo actuator 26 is obtained. The capacitance C of the piezo actuator 26 is an important parameter for the functional state of the piezo actuator 26. If, for example, the piezo actuator 26 breaks, this has a clear effect Change in capacitance C results. This can be recognized by using the diagnostic device 34. In the simplest case, we determined the

Capacity C is output as a numerical value from the diagnostic device 34.

The user can then use the numerical value to assess whether the piezo actuator 26 is OK or not.

However, it is also possible that the diagnostic device automatically detects the data in a corresponding evaluation circuit

Capacity compared with an upper and a lower limit.

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 piezo actuator 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, by means of which it is signaled that the piezo actuator 26 is not appears to be completely defective, but apparently it no longer fully meets the specification. On the other hand, 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 piezo actuator 26 is defective.

As can be seen from FIG. 3, the diagnostic device 34 is very simple, since a commercially available capacitor charging circuit 44 is used to provide the supply voltage and the supply current, which are applied or flowing to the piezo actuator 26 for the diagnosis. For example, it is possible to use a capacitor charging circuit of the type LT3420 (Linear Technology Magazine, May 2002), which is usually used to provide the trigger energy for xenon flash units of photomapps and has a capacitor with a capacitance of 220 μF, which within 3 , 5 s can be charged with a 5 V input voltage from 50 V to 320 V.

Since in the present diagnostic device 34, in contrast to a flash device of a camera, the piezo actuator 26 not only has to be charged, but also has to be discharged again, the electrical circuit of the diagnostic device 34 shown in FIG. 3 not only has a triggered charging signal 46, but also also via a discharge circuit 48 for constant current. The charging or discharging process is controlled by an operation amplifier 50 and two Schmitt triggers 52 and 54. In order to be able to control the course of the diagnosis in the diagnostic device 34, a microprocessor with an A / D converter is integrated in it. For connection to a PC, in particular a note book, the diagnostic device 34 also has a corresponding interface 56 (cf. FIG. 1). The circuit shown in FIG. 3 is supplied with current via the terminals 58. A built-in rechargeable battery, batteries, a connection to a network of the motor vehicle 12, a connection to a 230 V Metz voltage, or a supply via a photovoltaic converter are possible. A DC / DC converter 60 connected to the terminals 58 provides the energy for amplification circuits or, for example, the displays 38 to 42.

In the exemplary embodiment described in FIGS. 1 to 3, a diagnostic device 34 was shown, which in itself serves to diagnose a fuel injection device 22 installed in a motor vehicle 12. In principle, however, the proposed method and the proposed diagnostic device 34 can also be used by the motor vehicle manufacturer to check the fuel injectors 22 supplied before they are installed in the internal combustion engine 10 or 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 includes the power supply, all converters, an evaluation circuit, a control and a display processor, and the in a common housing

Displays 38 to 42, or alternatively or additionally, an LCD display, as well as the connecting cable 36 and the plug 32.

Claims

Claims 1. A method for diagnosing a fuel injection device (22) which has a piezo actuator (26) for actuating a valve element, characterized in that the fuel injection device (22) is connected directly to a diagnostic device (34) that by Diagnostic device (34) a specific voltage ^' (U) is applied to the piezo actuator (26), and that the diagnostic device (34) charges (Q) the charge introduced into the piezo actuator (26) and a capacitance (C) of the piezo actuator () 26) can be determined.

2. The method according to claim 1, characterized in that the diagnostic device (34) determines a course of the capacitance (C).

3. The method according to any one of claims 1 or 2, characterized in that the diagnostic device (34) compares the determined capacity (C) or the determined course of the capacity with at least one reference capacitance or a reference course and generates a signal depending on the result of the comparison.

4. The method according to claim 3, characterized in that on the basis of the signal an optical display (38,

40, 42) is activated with at least two colors, which indicate whether the determined capacity (C) or the course within a Tolerance range around the reference capacity or the reference curve.

5. The method according to any one of the preceding claims, characterized in that the applied voltage (U) during the diagnosis corresponds at least approximately to such a voltage (U) which occurs in normal operation of the fuel injection device (22).

6. The device (34) for carrying out a diagnostic method according to one of the preceding claims, characterized in that it has a capacitor charging circuit (44) which provides the energy required for controlling the piezo actuator (26).

7. The device (34) according to claim 6, characterized in that the capacitor charging circuit is a commercially available circuit (44) as used for flash units or the like.

8. The device (34) according to any one of claims 6 to 7, characterized in that it forms a closed structural unit.

9. The device (34) according to one of claims 6 to 8, characterized in that it comprises a connecting device (32) which is complementary to a connecting device (30) on the fuel injection device (22).

10. The device (34) according to any one of claims 6 to 9, characterized in that it has an interface (56) for connecting a PC.