Method for the injector-specific diagnosis of a fuel injection device and internal combustion engine having a fuel injection device

Abstract

A method for the injector-specific diagnosis of a fuel injection device of an internal combustion engine, including the following steps: detecting a pressure progression in an individual accumulator of an injector in a time-resolved manner; evaluating the detected pressure progression; determining if there is a fault state of the injection device in the region of the injector on the basis of the detected and evaluated pressure progression; and identifying the fault state on the basis of the detected and evaluated pressure progression.

Claims

1. A method for injector-specific diagnosis of a fuel injection device of an internal combustion engine, comprising the steps of: time-resolved recording of a pressure profile in an individual accumulator of an injector; evaluating the recorded pressure profile; determining whether there is a fault state of the injection device in a region of the injector based on the recorded and evaluated pressure profile; and identifying the fault state based on the recorded and evaluated pressure profile.

2. The method as claimed in claim 1, including recording the pressure profile in a time-resolved fashion in the individual accumulator synchronized with an energization of the injector, and/or assigning the recorded pressure profile to an injection event.

3. The method as claimed in claim 2, wherein the recording is synchronized simultaneously or overlapping with the energization.

4. The method as claimed in claim 2, further including checking whether the injector is energized.

5. The method as claimed in claim 4, including recording at least one energization value of the energization of the injector and using the recorded energization value to determine a fault state and/or to identify the fault state.

6. The method as claimed in claim 1, including determining a fault state and identifying the fault state as an absence of injection if the injector is energized, wherein a pressure drop in the pressure profile is not determined, or as an incorrect injection if the injector is not energized, wherein a pressure drop in the pressure profile is determined, or as a quantity-limiting valve fault of a quantity-limiting valve which is assigned to the injector, if a characteristic excessive increase is determined in the pressure profile, or as continuous injection, if an enduring pressure drop is detected, or as invalid injection, if an injection time which is obtained from the recorded pressure profile is outside a predetermined validity range, or as a level fault, if the recorded pressure profile undershoots or exceeds level limits which are predetermined after filtering, or as a noise fault, if noise of the recorded pressure profile exceeds a predetermined threshold value.

7. The method as claimed in claim 1, including identifying a defect of the fuel injection device when a fault state counter exceeds a predetermined maximum value, wherein a fault state counter is incremented if a fault state is determined, or a correction value which is obtained for the actuation of the injector exceeds a predetermined learning limit.

8. The method as claimed in claim 1, wherein a pressure sensor is used to record the pressure profile, at least one operating value being recorded by said pressure sensor, wherein a fault in the pressure sensor is identified if the at least one operating value exceeds or undershoots a predetermined threshold value or is outside a predetermined validity interval.

9. The method as claimed in claim 1, including applying the method to all the injectors of the internal combustion engine, wherein in the event of a fault state the faulty injector is identified.

10. The method as claimed in claim 1, including carrying out the method continuously or at predetermined time intervals during operation of the internal combustion engine.

11. An internal combustion engine, comprising: a fuel injection device that includes at least one injector that has an individual accumulator; a pressure sensor embodied and arranged so as to record pressure in the individual accumulator; and a control unit configured to carry out the method of claim 1, wherein the control unit is operatively connected to the pressure sensor, wherein the control unit includes a recorder for time-resolved recording of a pressure profile that is measured by the pressure sensor, wherein the control unit includes an evaluation unit for evaluating the recorded pressure profile, wherein the control unit includes a determining unit designed to determine, based on the recorded and evaluated pressure profile, whether there is a fault state of the injection device in a region of the injector, and wherein the control unit including an identification unit that identifies the fault state based on the recorded and evaluated pressure profile.

12. The internal combustion engine as claimed in claim 11, wherein the fuel injection device has a plurality of injectors as well as a common high-pressure accumulator for supplying the plurality of injectors with fuel.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The invention will be explained in more detail below with reference to the drawing, in which:

(2) FIG. 1 shows a schematic illustration of an exemplary embodiment of an internal combustion engine;

(3) FIG. 2 shows a schematic illustration of a first fault state;

(4) FIG. 3 shows a schematic illustration of a second fault state;

(5) FIG. 4 shows a schematic illustration of a third fault state;

(6) FIG. 5 shows a schematic illustration of a definition of specific validity ranges for injection times, and

(7) FIG. 6 shows a schematic illustration of the definition of predetermined level limits within the context of an embodiment of the method.

DETAILED DESCRIPTION OF THE INVENTION

(8) FIG. 1 shows a schematic illustration of an exemplary embodiment of an internal combustion engine 1. The latter has a fuel injection device 3 which comprises a multiplicity of injectors, of which only one injector 5 is illustrated here, for the sake of simplified illustration. The injector 5 has an individual accumulator 7. Furthermore, a quantity-limiting valve (not illustrated here) which is provided downstream of the individual accumulator 7 is integrated into the injector 5 and prevents an excessively large fuel quantity from being metered into a cylinder, assigned to the injector 5, of the internal combustion engine 1.

(9) A pressure sensor 9 is provided which is arranged on the injector 5 here in such a way that the pressure in the individual accumulator 7 can be recorded by means of the pressure sensor 9.

(10) A control unit 11 is provided which is operatively connected to the pressure sensor 9 in order to record the pressure in the individual accumulator 7. The control unit 11 has a recording means 13 for the time-resolved recording of a pressure profile which is measured by means of the pressure sensor 9. Furthermore, the control unit 11 has an evaluation means 15 for evaluating the recorded pressure profile, wherein said control unit 11 also has a determining means 17 which is designed to determine, on the basis of the recorded and evaluated pressure profile, whether there is a fault state of the injection device 3 in the region of the injector 5. The control unit 11 also comprises an identification means 19 with which the fault state can be identified on the basis of the recorded and evaluated pressure profile.

(11) In the illustrated exemplary embodiment, the fuel injection device 3 comprises a common high-pressure accumulator 21, which is also referred to as a common rail and which is fluidically connected to the injectors 5, and these are therefore supplied with fuel from the high-pressure accumulator 21.

(12) FIG. 2 shows a schematic illustration of a first fault state which can be determined and identified within the scope of the method. Here, FIG. 2 shows a diagram in which a pressure profile D which is recorded for an individual accumulator of an injector is plotted against a time axis characterized by t, as a continuous curve. In this context, a real time in physical units of time or as it were an intrinsic time of the internal combustion engine can be plotted on the time axis in units of an instantaneous angle of the crank shaft ( CA). An injection event in which the pressure profile in the individual accumulator exhibits a pressure drop owing to an injection is illustrated. The profile of an energization value B, which can be a current or a voltage which is recorded for the injector, is also illustrated as a dot-dashed line in FIG. 2.

(13) The fault state which is illustrated in FIG. 2 corresponds to an incorrect injection in which the injector is not energized, which is indicated by the constant profile of the energization value B. Nevertheless, a pressure drop takes place in the individual accumulator, which can be read off on the pressure profile D. Such an incorrect injection can occur, for example, owing to a defective pilot valve or as a result of a short circuit to ground.

(14) FIG. 3 shows an analogous, schematic illustration of a second fault state which is identified as an absence of injection. It is apparent here that the pressure profile D does not exhibit a pressure drop even though the profile of the energization value B indicates that the injector has been energized. Accordingly, there is a fault in which the injector does not open despite correct actuation.

(15) FIG. 4 shows a pressure profile D plotted against a time axis, characterized by t, for a fault state which is identified as continuous injection. In this case, a continuous pressure drop occurs in the individual accumulator, because a fluidic connection is continuously present between the individual accumulator and a cylinder, assigned to the injector, of the internal combustion engine.

(16) FIG. 5 shows a schematic illustration of the determination of an invalid injection. In this context, the pressure profile D is also plotted here against the time axis which is denoted by t. Two examples of setpoint injection times, specifically a setpoint start of injection SB and a setpoint end of injection SE, are also plotted as dashed, vertical lines. Corresponding values are preferably stored in characteristic diagrams, particularly preferably as a function of at least the rail pressure, particularly preferably of the rail pressure and a setpoint fuel quantity which is to be injected.

(17) For both setpoint injection times predetermined validity ranges are preferably stored, said validity ranges particularly preferably also being stored as characteristic diagrams, in particular as a function of the rail pressure. This is explained below merely for the setpoint start of injection SB for the sake of simpler illustration. However, the same statements apply equally well also to the setpoint end of injection SE.

(18) There are preferably two validity ranges distributed symmetrically about the setpoint start of injection SB, specifically a first unlearnt validity range .sub.u, which is entered here between two dot-dashed vertical lines, and a second, learnt validity range .sub.g which is smaller than the unlearnt validity range .sub.u, wherein its limits lie within the limits of the unlearnt validity range .sub.u. Here, the limits of the second learnt validity range .sub.g are illustrated by dotted vertical lines.

(19) Within the scope of the method, preferably a third, instantaneously applicable validity range is determined whose limits lie between the limits of the unlearnt validity range .sub.u and the learnt validity range .sub.g, wherein the third validity range is adapted to a learning progress of the injector under consideration.

(20) If, for example, a new injector is used, firstly the entire, unlearnt validity range .sub.u is applied as a validity range for the determination and identification of an invalid injection. It is apparent that as the learning progress continues, in that the correction values are adapted to the new injector in the corresponding correction characteristic diagrams of the control unit, the measured values which are actually recorded for the start of injection move closer to the setpoint start of injection SB. This learning progress is preferably recorded using a learning progress counter which is incremented if the obtained start of injection is located within the learnt validity range .sub.g. After the expiry of a certain time, for example an operating hour of the internal combustion engine, the learning progress counter is reduced again by a predetermined value, wherein both the time and the predetermined value are preferably parameterizable. Interpolation is carried out between the learnt validity range .sub.g and the unlearnt validity range .sub.u using the learning progress counter, with the result that the instantaneously applicable validity range always has at minimum the limits of the learnt validity range .sub.g and at maximum the limits of the unlearnt validity range .sub.u.

(21) An invalid injection is always determined when the obtained start of injection is outside the instantaneously applicable validity range. The instantaneously applicable validity range can be widened if an instantaneous fluctuation of the injector behavior occurs. For this purpose, a first validity counter is preferably provided which is incremented if the obtained start of injection lies inside the limits of the unlearnt validity range .sub.u and outside the limits of the learnt validity range .sub.g. If this first validity counter exceeds a predetermined maximum, the learning progress counter is preferably decremented and the instantaneously applicable validity range is increased. The first validity counter is preferably decremented if the obtained start of injection lies inside the limits of the learnt validity range .sub.g. In this context, the first validity counter preferably assumes at minimum the value zero, and therefore does not form any negative counter values.

(22) FIG. 6 shows a schematic and diagrammatic illustration relating to the determination and identification of a level fault. In this case, a first, predetermined upper level limit P1 and a second, lower predetermined level limit P2 are defined for the pressure profile, wherein the pressure profile D is intended to extend inside the level limits P1, P2 when the injection device is operating correctly.

(23) In one embodiment of the method it is possible that in this context a filtered and/or averaged pressure profile D is used as the basis for the consideration, which is indicated in FIG. 6 by the unbroken, smooth curve. This curve lies completely inside the level limits P1, P2 here, with the result that no level fault is determined.

(24) In an alternative embodiment of the method it is possible that the consideration is based on the unfiltered pressure profile, which is indicated here partially at the start of the curve profile D by an unfiltered curve D.sub.u which is represented partially. In this context, a tip of the unfiltered curve D.sub.u here projects beyond the upper level limit P1, and therefore in this case a fault state is determined and identified as a level fault.

(25) In one embodiment of the method there is provision that in order to determine and identify a fault state the unfiltered signal of the pressure sensor is compared with a separate filter result thereof, that is to say the signal after filtering, wherein a deviation of the unfiltered signal from the filtered signal is determined in order to ascertain to what extent harmonics, atypical values and/or noise are/is present on the unfiltered signal. It is possible here that a fault state is determined if the deviation of the unfiltered signal from the filtered signal goes beyond a predetermined extent.

(26) Overall it is apparent that the method and the internal combustion engine can be used to carry out a simple and at the same time very reliable and comprehensive on-board diagnosis of the individual injectors or of the fuel injection device in respect of numerous various fault states.