Fourier diagnosis of a charge cycle behavior of an internal combustion engine

Abstract

A diagnostic tool diagnoses a charge cycle behavior of an internal combustion engine with a plurality of cylinders. The diagnostic tool ascertains a rotational speed profile of the internal combustion engine. From the determined rotational speed curve, the diagnostic tool ascertains a peculiarity of at least one charge exchange characteristic variable by performing a Fourier transform. The diagnostic tool assigns a deviation type to the rotational speed profile as a function of the ascertained peculiarity of the charge exchange characteristic variable.

Claims

1. A method for diagnosing charge exchange behavior of an internal combustion engine with multiple cylinders, comprising: ascertaining a rotational speed profile of the internal combustion engine; ascertaining one or more amplitudes corresponding to each one or more engine orders using a Fourier transformation from the ascertained rotational speed profile; comparing the one or more amplitudes with predetermined amplitudes assigned to different deviation types, wherein the comparing comprises: calculating an amplitude difference between the one or more ascertained amplitudes and one or more of the predetermined amplitudes, and ascertaining that the amplitude difference is greater than a threshold value; and assigning a deviation type to the rotational speed profile as a result of the ascertaining that the amplitude difference is greater than the threshold value in accordance with the result of the comparing.

2. The method according to claim 1, wherein the Fourier transformation is a DFT and/or FFT calculation.

3. The method according to claim 1, further comprising: ascertaining the rotational speed profile during a diagnosis time window, which corresponds to at least one working cycle of the internal combustion engine.

4. A diagnostic tool for diagnosing charge exchange behavior of an internal combustion engine with multiple cylinders, the diagnostic tool comprising: a rotational speed acquisition unit to acquire a rotational speed of a crankshaft of the internal combustion engine; and a processor configured to: control the rotational speed acquisition unit; ascertain one or more amplitudes corresponding to each of one or more engine orders using a Fourier transformation from an ascertained rotational speed profile; compare the one or more amplitudes with predetermined amplitudes assigned to different deviation types, wherein the comparing comprises: calculating an amplitude difference between the one or more ascertained amplitudes and one or more of the predetermined amplitudes, and ascertaining that the amplitude difference is greater than a threshold value; and assign a deviation type to the rotational speed profile as a result of the ascertaining that the amplitude difference is greater than the threshold value in accordance with the result of the comparing.

5. An internal combustion engine with multiple cylinders comprising the diagnostic tool of claim 4.

6. The method of claim 1, further comprising: comparing the ascertained rotational speed profile with a plurality of deviation-typical rotational speed profiles; and subjecting the ascertained rotational speed profile and at least one of the deviation-typical rotational speed profiles to the Fourier transformation.

7. The diagnostic tool according to claim 4, wherein the processor is further configured to: compare the ascertained rotational speed profile with a plurality of deviation-typical rotational speed profiles; and subject the ascertained rotational speed profile and at least one of the deviation-typical rotational speed profiles to the Fourier transformation.

8. The method according to claim 1, wherein the different deviation types include at least one selected from the group consisting of: insufficient charging of a cylinder with fresh air and/or recirculated exhaust gas; excessive charging of the cylinder with fresh air and/or recirculated exhaust gas; insufficient compression of the cylinder; excessive mechanical friction in the cylinder; and premature ignition of the cylinder, and a plurality of different threshold values are each assigned to the different deviation types for different operating points of the internal combustion engine.

9. The method according to claim 1, wherein the threshold value is fixed for the deviation type at an engine operating point.

10. The method of claim 9, wherein the engine operating point is defined by a rotational speed and a load situation of the internal combustion engine.

11. The diagnostic tool according to claim 4, wherein the threshold value is fixed for the deviation type at an engine operating point.

12. The method of claim 1, further comprising: subjecting the rotational speed profile to the Fourier transformation prior to the calculating of the difference between the ascertained one or more amplitudes and the one or more predetermined amplitudes.

13. The diagnostic tool according to claim 4, wherein the different deviation types include at least one selected from the group consisting of: insufficient charging of a cylinder with fresh air and/or recirculated exhaust gas; excessive charging of the cylinder with fresh air and/or recirculated exhaust gas; insufficient compression of the cylinder; excessive mechanical friction in the cylinder; and premature ignition of the cylinder, and a plurality of different threshold values are each assigned to the different deviation types for different operating points of the internal combustion engine.

14. The diagnostic tool according to claim 4, wherein the processor is further configured to: ascertain the rotational speed profile during a diagnosis time window, which corresponds to at least one working cycle of the internal combustion engine.

15. The diagnostic tool according to claim 11, wherein the engine operating point is defined by a rotational speed and a load situation of the internal combustion engine.

16. The diagnostic tool according to claim 4, wherein the processor is further configured to: subject the rotational speed profile to the Fourier transformation prior to the calculating of the difference between the ascertained one or more amplitudes and the one or more predetermined amplitudes.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIGS. 1a-1c show, in schematic views, an internal combustion engine with a diagnostic tool according to an example embodiment of the present subject matter.

(2) FIG. 1a illustrates the installation environment of the internal combustion engine.

(3) FIG. 1b illustrates relevant parameters.

(4) FIG. 1c illustrates torque contributions to the crank drive of the internal combustion engine versus the time.

(5) FIGS. 2a-2b show a rotational speed profile of the engine as per FIG. 1a (see FIG. 2a).

(6) FIG. 2b is an illustration of an engine order analysis versus this rotational speed profile, in each case for a fault-free operating state and for an operating state with a leakage of the supercharging air system.

(7) FIG. 3 shows a diagnosis characteristic map versus the engine load and the engine rotational speed, in which diagnosis characteristic map a range of a threshold value exceedance with respect to the amplitude difference plotted in FIG. 2b is indicated.

DETAILED DESCRIPTION OF THE DRAWINGS

(8) FIG. 1a illustrates an internal combustion engine 1 in its installation environment, wherein the internal combustion engine 1 is, in the example embodiment, a four-stroke engine with 4 cylinders Z1, Z2, Z3 and Z4.

(9) Of the installation environment, the illustration of FIG. 1a shows the intake system 9 with the air filter LF at the air inlet, the exhaust-gas turbocharger ATL and a charge-air cooling arrangement and the air manifold LS in the direction of the cylinders Z. Also shown are potential leakage regions L at the pipelines between the various components. By way of example, a potential mechanical failure R at the piston and/or at the cylinder inner wall, which would potentially lead to greatly increased friction, is signaled at the cylinder Z1.

(10) FIG. 1b illustrates the internal combustion engine 1 in a more detailed schematic view. The internal combustion engine 1 has the cylinders Z1, Z2, Z3 and Z4, wherein all the cylinders Z provide a torque contribution M to the crank drive KT. The internal combustion engine 1 additionally has a diagnostic tool 2 according to an example embodiment of the present subject matter, which diagnostic tool has a processing unit 4, a rotational speed acquisition unit 6 and optionally a pressure acquisition unit 7 for the reference pressures from surroundings and air manifold or crankcase. The optional pressure acquisition unit 7 operates by reading the values to be ascertained out of an operation model, for example of the engine controller.

(11) From FIG. 1b, it can be seen inter alia that each cylinder Z can cyclically provide a torque contribution M to the crank drive KT in a manner dependent on the respective cylinder pressure p. The totality of the torque contributions results in a rotational speed n of a crankshaft of the crank drive KT which varies over time.

(12) The present rotational speed n can be ascertained using the rotational speed acquisition unit 6 and the processing unit 4 and used by the diagnostic tool 2.

(13) FIG. 1c illustrates an example torque profile 10 at the crank drive KT during normal operation at an operating point (rotational speed; load state) versus the crank angle KW. It can be seen that the torque contribution M originates from different cylinders Z in alternating fashion. Exactly one working cycle (=a KW range of 720°) of the four-cylinder engine 1, which is in the form of a four-stroke engine, is illustrated.

(14) The illustrated working cycle corresponds, in the example embodiment, to a diagnosis time window 20 used for the ascertainment of the rotational speed profile 101 (cf. also FIG. 2a).

(15) In the example embodiment, for the internal combustion engine 1 according to FIG. 1, the twelfth engine order MO12 (the engine orders are frequencies normalized versus the rotational speed, to be able to work with the same feature over the entire characteristic map range). The method described by way of example is optimized for 4-cylinder engines, though may possibly also be used, in analogously adapted form, for other numbers of cylinders. The basis for the diagnosis described in the example embodiment is the third multiple of the basic excitation frequency of the engine 1 (in relation to one working cycle=four strokes in the case of a four-cylinder four-stroke engine).

(16) FIG. 2a illustrates a diagram with rotational speed developments 100 during a diagnosis time window 20. The diagram shows a rotational speed profile 101 that has been ascertained using the rotational speed acquisition unit 6. Furthermore, the diagram shows the rotational speed profile 101′, which has been read out from an operation tool of the engine controller, where said rotational speed profile is stored, for the considered reference point of the engine at 3000 revolutions per minute and a defined load situation, as a deviation-typical rotational speed profile for the case of a leakage L in the intake air system.

(17) In the context of the example method, the ascertained rotational speed profile 101 is furthermore compared with further rotational speed profiles which are stored in the operation model for other potential fault situations, which rotational speed profiles are however not illustrated in FIG. 2a for the sake of simplicity. The example embodiment will thus be described by way of example below for the identification of the deviation type of leakage L in the intake air system.

(18) It can be seen from FIG. 2a that the ascertained rotational speed profile 101 and the deviation-typical rotational speed profile 101′ differ from one another. To be able to better analyze the different profiles 101 and 101′, the two profiles are subjected to a Fourier transformation using an FFT method or possibly using a DFT method.

(19) FIG. 2b illustrates the result of these Fourier transformations in the form of an order analysis relating to the engine orders MO1 to MO¬25 versus the amplitude A. For each engine order, the ascertained amplitude AMO is illustrated by a triangle and the deviation-typical amplitude AMO′ is illustrated by a circle.

(20) From this, it is possible, in a comparison, to ascertain an amplitude difference ΔAMO=AMO-AMO′.

(21) If this amplitude difference ΔAMO is greater than a threshold value which is fixed for the deviation type at the considered engine operating point (defined by the rotational speed n and the load situation we) and which is stored in the operation model, the example method yields, for the operating point under examination, the result that the corresponding deviation type is present.

(22) In the example embodiment illustrated in FIG. 2, the twelfth engine order MO12 is correspondingly examined in the order analysis 200. For this engine order, the amplitude difference is calculated as ΔA12=A12−A12′. If ΔA12 is greater than the threshold value, fixed for the operating situation, regarding the deviation type of a leakage L in the intake air system, the engine 1 is assigned the deviation type L for this operating point.

(23) FIG. 3 illustrates a diagnostic characteristic map 300 for the twelfth engine order MO12 regarding the identification of the deviation type L, broken down according to operating points, which are defined by a combination of the rotational speed n under examination and the load situation we under examination. For the engine operating points in the region of the characteristic map 300 stored with dark coloring, the amplitude difference ΔA12 is greater than the threshold value, such that the deviation type L is identified. For the engine operating points in the region of the characteristic map 300 stored with light coloring, the amplitude difference is smaller than the threshold value, such that the deviation type is not identified.

(24) The illustration of FIG. 3 shows an evaluation over multiple diagnosis time windows 20 over the entire characteristic map, wherein, for the considered multiplicity of method implementations, the statistical significance of the illustrated results is considerably increased by applying a t-test. The effect of outliers on the illustrated results is thus almost eliminated.

(25) The described order analysis using FFT transformation may be performed analogously for each working cycle or for each revolution (correspondingly twelfth or sixth order in the case of four-cylinder engines) and, on the one hand, compared with stored knowledge from a lookup table from an operation model, for example of the engine controller. Alternatively, using a rotational speed simulation, the residual between measured and simulated variable may be compensated. In the event of exceedance of the threshold value, a fault is present, analogously to the above description, which fault can be assigned to the deviation type of a leakage.

(26) For use in the case of other engines, it is possible, in accordance with example methods analogous to this example, and with otherwise analogous application, to analyze the respectively corresponding multiple of the base excitation order of the engine, in particular the sixth order (two-cylinder engine), the ninth order (three-cylinder engine with four strokes in the working cycle) or the 18th order (six-cylinder four-stroke engine, resolved by working cycle).

LIST OF REFERENCE DESIGNATIONS

(27) 1 Internal combustion engine 2 Diagnostic tool 4 Processing unit 6 Acquisition unit for the rotational speed of the crankshaft 7 Pressure acquisition unit 9 Intake system 10 Torque profile of the internal combustion engine over one engine cycle 20 Diagnosis time window 100 Diagram of rotational speed development 101 Rotational speed profile A Amplitude relating to an engine order ΔA Amplitude difference ATL Exhaust-gas turbocharger KT Crank drive KW Crank angle L Potential leakages LF Air filter LS Air manifold M Torque of a cylinder in FIG. 1 MO Engine order n Rotational speed p Cylinder pressure in FIG. 1 R Potential mechanical fault as a result of piston/cylinder friction we Load situation [kj/L] Z Cylinder.