Method for diagnosing errors in an internal combustion engine

Abstract

A method is described for diagnosing errors in an internal combustion engine in which fuel is injected from a high-pressure accumulator into associated combustion chambers with the aid of multiple fuel injectors, a first value (R.sub.stat,2) which is representative of a static flow rate of fuel through one of the fuel injectors being ascertained, a second value (n) which is representative of a running smoothness of the internal combustion engine being ascertained, if at least one of the two values (R.sub.stat,2, n) deviates from the particular associated reference value (R.sub.stat, n.sub.0), an error (F) being deduced, and the error (F) being assigned to the fuel injector and/or at least one further component and/or at least one operating phase of the internal combustion engine on the basis of deviations of the two representative values (R.sub.stat,2, n) from the particular associated reference value (R.sub.stat, n.sub.0).

Claims

1. A method for diagnosing an error in an internal combustion engine in which fuel is injected from a high-pressure accumulator into associated combustion chambers with the aid of multiple fuel injectors, the method comprising: ascertaining a first value that represents a static flow rate of fuel through one of the fuel injectors, the ascertaining of the first value including determining a quotient of: (i) a pressure drop in the high-pressure accumulator during a fuel injection by the one of the fuel injectors, and (ii) a time duration of the fuel injection by the one of the fuel injectors; ascertaining a second value that represents a running smoothness of the internal combustion engine, the ascertaining of the second value including determining a rotational speed fluctuation of the internal combustion engine, wherein the rotational speed fluctuation of the internal combustion engine is a deviation of a maximally occurring rotational speed of the internal combustion engine from a mean value of the rotational speed of the internal combustion engine; comparing the first value to a first reference value; comparing the second value to a second reference value; based on the comparing of the first value and the comparing of the second value, detecting the error, the error being detected by at least one of: (1) detecting a deviation of the first value from the first reference value, and (2) detecting a deviation of the second value from the second reference value; and determining the error is attributable to: (1) the one of the fuel injectors when the deviation of the first value from the first reference value is detected, and (2) at least one further component of the internal combustion engine or at least one operating phase of the internal combustion engine when the deviation of the second value from the second reference value is detected, and (3) both (i) the one of the fuel injectors, and (ii) the at least one further component of the internal combustion engine or the at least one operating phase of the internal combustion engine, when both (i) the deviation of the first value from the first reference value is detected and (ii) the deviation of the second value from the second reference value is detected.

2. The method as recited in claim 1, wherein at least one of: the at least one further component of the internal combustion engine includes an air supply system of the internal combustion engine or an ignition device of the internal combustion engine; and the at least one operating phase of the internal combustion engine includes a compression of an air/fuel mixture in the internal combustion engine or an ignition process in the internal combustion engine.

3. The method as recited in claim 1, further comprising: when the error is determined to be attributable to the at least one further component of the internal combustion engine or the at least one operating phase of the internal combustion engine, carrying out a more detailed diagnosis of the error out under consideration of a lambda control.

4. The method as recited in claim 1, further comprising: storing a piece of information about the error in an error memory when at least one of: the first value deviates from the first reference value by more than a first threshold value, and the second value deviates from the second reference value by more than the first threshold value.

5. The method as recited in claim 4, wherein the internal combustion engine is included in a motor vehicle, and wherein the method further comprises: outputting a warning to a driver of the motor vehicle when (1) the first value deviates from the first reference value by more than a second threshold value, or (2) the second value deviates from the second reference value by more than the second threshold value; wherein the warning is output by activating a malfunction indicator light in the motor vehicle or displaying a message in the motor vehicle; and wherein the second threshold value is greater than the first threshold value.

6. The method as recited in claim 1, further comprising: detecting and storing a profile of a deviation of at least one of the first value from the first reference value and the second value from the second reference value over a mileage of the internal combustion engine.

7. The method as recited in claim 1, further comprising: ascertaining the first reference value by determining a mean of ascertained respective first values of all fuel injectors of the internal combustion engine except the one of the fuel injectors, wherein each of the first values is ascertained by determining a quotient of: (i) a pressure drop in the high-pressure accumulator during a fuel injection by the respective fuel injector, and (ii) a time duration of the fuel injection by the respective fuel injector.

8. The method as recited in claim 1, further comprising: prior to ascertaining the first value and the second value, reducing at least one of: (i) deviations of the static flow rates, and (ii) deviations of open durations during injection processes, in each case among different fuel injectors of the internal combustion engine.

9. The method as recited in claim 8, wherein the at least one of the deviations of the static flow rates and the deviations of the open durations during the injection processes are reduced by being minimized.

10. A processing unit for diagnosing an error in an internal combustion engine in which fuel is injected from a high-pressure accumulator into associated combustion chambers with the aid of multiple fuel injectors, the processing unit being adapted to: ascertain a first value that represents a static flow rate of fuel through one of the fuel injectors, the processing unit being adapted to ascertain the first value by determining a quotient of: (i) a pressure drop in the high-pressure accumulator during a fuel injection by the one of the fuel injectors, and (ii) a time duration of the fuel injection by the one of the fuel injectors; ascertain a second value that represents a running smoothness of the internal combustion engine, the processing using being adapted to ascertain the second value by determining a rotational speed fluctuation of the internal combustion engine, wherein the rotational speed fluctuation of the internal combustion engine is a deviation of a maximally occurring rotational speed of the internal combustion engine from a mean value of the rotational speed of the internal combustion engine; detect the error if: at least one of (1) the first value deviates from a first reference value, and (2) the second value deviates from a second reference value; and if the error is detected, determine the error is attributable to: (1) the one of the fuel injectors if the first value deviates from the first reference value, and (2) at least one further component of the internal combustion engine, or at least one operating phase of the internal combustion engine if the second value deviates from the second reference value, and (3) both (i) the one of the fuel injectors, and (ii) the at least one further component of the internal combustion engine or the at least one operating phase of the internal combustion engine, if both (i) the first value deviates from the first reference value, and (ii) the second value deviates from the second reference value.

11. The processing unit according to claim 10, wherein the processing unit is further configured to ascertain the first reference value by determining a mean of ascertained respective first values of all fuel injectors of the internal combustion engine except the one of the fuel injectors, wherein each of the first values is ascertained by determining a quotient of: (i) a pressure drop in the high-pressure accumulator during a fuel injection by the respective fuel injector, and (ii) a time duration of the fuel injection by the respective fuel injector.

12. A computer program that prompts a processing unit to carry out a method for diagnosing an error in an internal combustion engine in which fuel is injected from a high-pressure accumulator into associated combustion chambers with the aid of multiple fuel injectors, the method comprising: ascertaining a first value that represents a static flow rate of fuel through one of the fuel injectors, the ascertaining of the first value including determining a quotient of: (i) a pressure drop in the high-pressure accumulator during a fuel injection by the one of the fuel injectors, and (ii) a time duration of the fuel injection by the one of the fuel injectors; ascertaining a second value that represents a running smoothness of the internal combustion engine, the ascertaining of the second value including determining a rotational speed fluctuation of the internal combustion engine, wherein the rotational speed fluctuation of the internal combustion engine is a deviation of a maximally occurring rotational speed of the internal combustion engine from a mean value of the rotational speed of the internal combustion engine; detect the error if: at least one of (1) the first value deviates from a first reference value, and (2) the second value deviates from a second reference value; and if the error is detected, determining the error is attributable to: (1) the one of the fuel injectors if the first value deviates from the first reference value, and (2) at least one further component of the internal combustion engine, or at least one operating phase of the internal combustion engine if the second value deviates from the the second reference value, and (3) both (i) the one of the fuel injectors, and (ii) the at least one further component of the internal combustion engine or the at least one operating phase of the internal combustion engine, if both (i) the first value deviates from the first reference value, and (ii) the second value deviates from the second reference value.

13. A non-transitory machine-readable memory medium on which is stored a computer program for diagnosing an error in an internal combustion engine in which fuel is injected from a high-pressure accumulator into associated combustion chambers with the aid of multiple fuel injectors, the computer program, when executed by a processing unit, causing the processing unit to perform the following steps: ascertaining a first value that represents a static flow rate of fuel through one of the fuel injectors, the ascertaining of the first value including determining a quotient of: (i) a pressure drop in the high-pressure accumulator during a fuel injection by the one of the fuel injectors, and (ii) a time duration of the fuel injection by the one of the fuel injectors; ascertaining a second value that represents a running smoothness of the internal combustion engine, the ascertaining of the second value including determining a rotational speed fluctuation of the internal combustion engine, wherein the rotational speed fluctuation of the internal combustion engine is a deviation of a maximally occurring rotational speed of the internal combustion engine from a mean value of the rotational speed of the internal combustion engine; detecting the error if: at least one of (1) the first value deviates from a first reference value, and (2) the second value deviates from a second reference value; and if the error is detected, determining the error is attributable to: (1) the one of the fuel injectors if the first value deviates from the first reference value, and (2) at least one further component of the internal combustion engine, or at least one operating phase of the internal combustion engine if the second value deviates from the the second reference value, and (3) both (i) the one of the fuel injectors, and (ii) the at least one further component of the internal combustion engine or the at least one operating phase of the internal combustion engine, if both (i) the first value deviates from the first reference value, and (ii) the second value deviates from the second reference value.

14. The non-transitory machine-readable memory medium according to claim 13, wherein the computer program, when executed by the processing unit, further causes the processing unit to perform the following step: ascertaining the first reference value by determining a mean of ascertained respective first values of all fuel injectors of the internal combustion engine except the one of the fuel injectors, wherein each of the first values is ascertained by determining a quotient of: (i) a pressure drop in the high-pressure accumulator during a fuel injection by the respective fuel injector, and (ii) a time duration of the fuel injection by the respective fuel injector.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 schematically shows an internal combustion engine including a common-rail system which is suitable for carrying out a method according to the present invention.

(2) FIG. 2 shows in a diagram a flow volume in a fuel injector over time.

(3) FIG. 3 shows in a diagram a pressure profile in a high-pressure accumulator during an injection process.

(4) FIG. 4 shows in a diagram a rotational speed profile of the internal combustion engine including rotational speed fluctuations and an associated reference value in a method according to the present invention in one preferred specific embodiment.

(5) FIG. 5 shows a first value which is representative of a static flow rate and an associated reference value in a method according to the present invention in one preferred specific embodiment.

(6) FIG. 6 schematically shows a sequence of a method according to the present invention in one preferred specific embodiment.

DETAILED DESCRIPTION

(7) FIG. 1 schematically shows an internal combustion engine 100 which is suitable for carrying out a method according to the present invention. Internal combustion engine 100 includes three combustion chambers or associated cylinders 105 by way of example. Each combustion chamber 105 is assigned a fuel injector 130 which, in turn, is connected in each case to a high-pressure accumulator 120, a so-called rail, via which it is supplied with fuel. It is understood that a method according to the present invention may also be carried out in an internal combustion engine including any arbitrary number of cylinders, for example four, six, eight or twelve cylinders.

(8) High-pressure accumulator 120 is further fed with fuel from a fuel tank 140 via a high-pressure pump 110. High-pressure pump 110 is coupled to internal combustion engine 100, namely in such a way, for example, that the high-pressure pump is driven via a crankshaft of the internal combustion engine or via a camshaft which, in turn, is coupled to the crankshaft. Furthermore, an air supply system 150 is shown via which air may be supplied to individual combustion chambers or cylinders 105.

(9) Fuel injectors 130 are activated to meter fuel into particular combustion chambers 105 via a processing unit which is designed as an engine control unit 180. For the sake of clarity, only the connection from engine control unit 180 to one fuel injector 130 is illustrated, it is understood however, that each fuel injector 130 is correspondingly connected to the engine control unit. Each fuel injector 130 may be specifically activated in this case. Furthermore, engine control unit 180 is configured to detect the fuel pressure in high-pressure accumulator 120 with the aid of a pressure sensor 190.

(10) In the diagram of FIG. 2, a cumulative flow volume V through a fuel injector over time t is illustrated in the case of a long-lasting activation of the fuel injector. At point in time t.sub.0, an activation time starts and at point in time t.sub.1, the valve needle starts to lift. Thus, an open duration of the fuel injector also starts at point in time t.sub.1. It is apparent in this case that cumulative flow volume V or the fuel quantity flown through the fuel injector constantly increases across a wide range following a short period of time while the valve needle is lifting. In this range, the valve needle is in a so-called full lift, i.e. the valve needle is lifted completely or up to a setpoint height.

(11) During this time, a constant fuel quantity flows per time unit through the valve opening of the fuel injector, i.e. static flow rate Q.sub.stat which indicates the increase in the cumulative flow volume V, is constant. In this case, the magnitude of the static flow rate is a crucial factor which, as already mentioned at the outset, determines the fuel quantity injected overall during an injection process. Deviations or tolerances in the static flow rate therefore affect the injected fuel quantity per injection process.

(12) At point in time t.sub.2, the activation time ends and the closing time starts. The valve needle starts to lower itself in the process. The closing time and the open duration end at point in time t.sub.3 when the valve needle again completely closes the valve.

(13) In the diagram of FIG. 3, a pressure profile in a high-pressure accumulator during an injection process is illustrated over time t. It is apparent in this case that pressure p is essentially constant in the high-pressure accumulator, apart from certain fluctuations due to pump deliveries. During the injection process, which takes place for a time duration t, pressure p drops in the high-pressure accumulator by a value p.

(14) Subsequently, pressure p remains at the lower level, again apart from certain fluctuations, until pressure p increases again to the starting level as a result of a subsequent delivery by the high-pressure pump.

(15) These pressure drops during injection processes are detected and evaluated with the aid of the usually already present components, for example pressure sensor 190 and engine control unit 180, including the appropriate input circuit. Additional components are therefore not necessary. This evaluation takes place for each combustion chamber 105 individually.

(16) Static flow rate Q.sub.stat through the fuel injector is characterized, as already mentioned, by the injected fuel quantity or its volume per time. In a high-pressure accumulator or rail pumped up to the system pressure, the injected volume is proportional to the pressure drop in the rail. The associated time duration corresponds in this case to the open duration of the fuel injector which may be determined mechatronically with the aid of a so-called CVO (see for example DE 10 2009 002 593 A1), for example, as mentioned at the outset.

(17) By forming a quotient between pressure drop or pressure difference p and open duration or time duration of the injection t, a pressure rate is obtained as a replacement value or a first representative value R.sub.stat=p/t for static flow rate Q.sub.stat, i.e. for a measuring operation

(18) $Q_{\mathrm{stat}}\frac{p}{t}$
applies. A subsequent delivery by the high-pressure pump should not take place in the relevant time window, in this case. A subsequent delivery is therefore to be suppressed, if necessary.

(19) In order to increase the accuracy of first representative value R.sub.stat, it is possible, for example, to carry out a mean value formation over multiple such injection processes.

(20) If, for example, a mean value of the individual first representative values of all fuel injectors is used as the first reference value which is associated with the first representative value, a deviation of a fuel injector is ascertained with regard to its first representative value and is reduced or minimized as compared to the first reference value. This may also be carried out for multiple or all fuel injectors.

(21) It is also conceivable that all fuel injectors, except for the one which is to be checked at the time, are used when computing the first reference value.

(22) In the diagram of FIG. 4, a rotational speed profile of the internal combustion engine is illustrated including rotational speed fluctuations as a second value representative of the running smoothness. For this purpose, rotational speed n is plotted against time t. Rotational speed fluctuation n, here the maximum deviation of rotational speed n as compared to a mean value n.sub.0, may be used in this case as a measure for the running smoothness of the internal combustion engine.

(23) As the associated, second reference value, rotational speed fluctuation n.sub.0 may be used, for example. In this case, it should be taken into account that certain rotational speed fluctuations, i.e. deviations of the maximally occurring value from the mean value, generally always occur and therefore a deviation of a rotational speed fluctuationas defined herefrom mean value no cannot already be assumed.

(24) It is advantageous, however, that a deviation of the second representative value from the associated reference value is only considered as detected, if the deviation from associated reference value n.sub.0 is greater than first associated threshold value n.sub.1 (shown in the present case), in order to take into account potential measuring tolerances.

(25) It is, however, also conceivable to use as the second representative value a mean rotational speed, averaged over a certain number, for example one, two, or three, rotations of the internal combustion engine. In this case, mean value no, which should then be ascertained over a considerably higher number of rotations, for example 20 or 30, may be used as the associated second reference value.

(26) First threshold value n.sub.1 as well as second threshold value n.sub.2, which is also shown and belongs to the rotational speed fluctuation, will be elucidated in greater detail below.

(27) In the diagram of FIG. 5, three representative values R.sub.stat,1, R.sub.stat,2, and R.sub.stat,3 are shown, such as the ones which may be ascertained for the fuel injectors shown in FIG. 1, for example, according to the method elucidated above.

(28) Furthermore, a first reference value R.sub.stat is shown which is obtained as an arithmetic mean value, for example, from the two representative values R.sub.stat,1 and R.sub.stat,3 by way of example. The first reference value is thus ascertained from all other fuel injectors, except for the checked fuel injector. It is also conceivable, however, that the first reference value is ascertained from all three (i.e. all present) fuel injectors, i.e. including the checked fuel injector.

(29) A deviation of the second representative value, R.sub.stat,2 in this case, from associated reference value R.sub.stat may now be considered as detected, for example, if second representative value R.sub.stat,2 deviates from reference value R.sub.stat at all. Preferably, a deviation should only be considered as detected, if the deviation is greater than a certain threshold value, in particular also in order to take into account potential measuring tolerances. Here, a first threshold value R.sub.1 may be involved, for example, which belongs to the second representative value.

(30) First threshold value R.sub.1 as well as second threshold value R.sub.2, which is also shown and belongs to the second representative value, shall be elucidated in greater detail below.

(31) FIG. 6 schematically shows a sequence of a method according to the present invention in one preferred specific embodiment. Initially, the deviations of the static flow rates and/or deviations of open durations during injection processes may be reduced, in particular minimized, among different fuel injectors of the internal combustion engine, as was mentioned at the outset with regard to the CVO, for example.

(32) Furthermore, the deviations of the fuel injectors with regard to their first representative values may be ascertained and reduced or minimized as compared to the first reference value, as was also already mentioned, inter alia, with reference to FIG. 3.

(33) Furthermore, first representative value R.sub.stat,2 may now be checked, as shown, with regard to a deviation from associated, first reference value R.sub.stat. For this purpose, the first representative value may be ascertained again after reducing or minimizing the deviation of the first representative value. Furthermore, second representative value n may now be checked with regard to a deviation from associated, second reference value n.sub.0.

(34) A deviation may be considered as detected if the particular representative value deviates from the particular reference value by more than the particular first threshold value, for example, as was elucidated in greater detail with reference to FIGS. 4 and 5.

(35) If now at least one of the two representative values R.sub.stat,2 or n deviates from associated reference values R.sub.stat or n.sub.0, an error F may be deduced.

(36) Depending on whether only one of the two representative values deviates from the associated reference value or whether both representative values deviate from the associated reference values, the error may now be assigned differently.

(37) If only first representative value R.sub.stat,2 deviates from associated reference value R.sub.stat, the error is assigned to the appropriate fuel injector, as is indicated in this case with the aid of reference numeral F.sub.1.

(38) If only second representative value n deviates from associated reference value n.sub.0, the error is assigned to the at least one other component and/or the at least one operating phase of the internal combustion engine, as is indicated in this case with the aid of reference numeral F.sub.2.

(39) If both representative values R.sub.stat,2 and n deviate from associated reference values R.sub.stat and n.sub.0, respectively, the error is assigned to the fuel injector and the at least one other component and/or the at least one operating phase of the internal combustion engine, as is indicated in this case with the aid of reference numeral F.sub.3.

(40) As far as more detailed elucidations with regard to the assignment of the error are concerned, reference is made to the above-mentioned explanations to avoid repetitions.

(41) If the representative value (or, depending on the situation, both) deviate(s) from the associated reference value by more than the particular first threshold value, but by less than the particular second threshold value, as is shown in FIG. 5 for the first representative value, for example, the information about the error may be stored in an error memory, for example.

(42) If, for example, one of the representative values were to deviate from the associated reference value by more than the particular threshold value during a later check, a warning may be output to a driver, for example.