Detecting Cylinder-Specific Combustion Profile Parameter Values For An Internal Combustion Engine

Abstract

A method for detecting a cylinder-specific combustion profile parameter value for an internal combustion engine is described. The method includes the following: (a) detecting a toothed encoder signal, (b) determining a cylinder-specific tooth time interval on the basis of the toothed encoder signal, (c) determining a cylinder-specific phase value on the basis of a Fourier transformation of a part of the toothed encoder signal corresponding to the cylinder-specific tooth time interval, (d) determining the combustion profile parameter value on the basis of the cylinder-specific phase value and a stored transfer function which represents a relationship between the combustion profile parameter and the phase value.

Claims

1. A method for detecting a cylinder-specific combustion profile parameter value for an internal combustion engine, the method comprising: detecting a toothed encoder signal; determining a cylinder-specific tooth time interval based on the toothed encoder signal; determining a cylinder-specific phase value based on a Fourier transformation of a part of the toothed encoder signal corresponding to the cylinder-specific tooth time interval; and determining the combustion profile parameter value based on the cylinder-specific phase value and a stored transfer function which represents a relationship between the combustion profile parameter and the phase value.

2. The method as claimed in claim 1, wherein the determination of the cylinder-specific phase value also comprises an offset correction for determining an offset-corrected cylinder-specific phase value.

3. The method as claimed in claim 2, wherein the offset correction comprises determining a mean value of a multiplicity of cylinder-specific phase values during an overrun phase.

4. The method as claimed in claim 3, wherein the offset-corrected cylinder-specific phase value is determined by subtracting the determined mean value from the cylinder-specific phase value.

5. The method as claimed in claim 1, wherein the combustion profile parameter value is determined based on a mean value of a plurality of cylinder-specific phase values of a cylinder.

6. The method as claimed in claim 1, wherein the internal combustion engine has a reference cylinder with a cylinder pressure sensor, the method also comprising: detecting a pressure value for the reference cylinder; determining the combustion profile parameter value for the reference cylinder based on the pressure value; determining the cylinder-specific phase value both for the reference cylinder and for a further cylinder; and determining the combustion profile parameter value for the further cylinder based on the combustion profile parameter value for the reference cylinder, the phase value for the reference cylinder, the phase value for the further cylinder and the stored transfer function.

7. The method as claimed in claim 6, further comprising: calculating a difference between the value of the transfer function for the phase value of the further cylinder and the value of the transfer function for the phase value of the reference cylinder, wherein the combustion profile parameter value for the further cylinder is determined by adding the combustion profile parameter value for the reference cylinder and the calculated difference.

8. The method as claimed in claim 1, wherein the cylinder-specific combustion profile parameter value is a burnt fuel mass fraction MFBxx.

9. The method as claimed in claim 8, wherein the burnt fuel mass fraction MFBxx is an MFB50 value.

10. A control device for an internal combustion engine, the control device comprising: a data memory storing a transfer function; and a processing unit configured to carry out a method for detecting a cylinder-specific combustion profile parameter value for an internal combustion engine, the method comprising: detecting a toothed encoder signal; determining a cylinder-specific tooth time interval based on the toothed encoder signal; determining a cylinder-specific phase value based on a Fourier transformation of a part of the toothed encoder signal corresponding to the cylinder-specific tooth time interval; and determining the combustion profile parameter value based on the cylinder-specific phase value and a stored transfer function which represents a relationship between the combustion profile parameter and the phase value.

11. The method as claimed in claim 10, wherein the determination of the cylinder-specific phase value also comprises an offset correction for determining an offset-corrected cylinder-specific phase value.

12. The method as claimed in claim 11, wherein the offset correction comprises determining a mean value of a multiplicity of cylinder-specific phase values during an overrun phase.

13. The method as claimed in claim 12, wherein the offset-corrected cylinder-specific phase value is determined by subtracting the determined mean value from the cylinder-specific phase value.

14. The method as claimed in claim 10, wherein the combustion profile parameter value is determined based on a mean value of a plurality of cylinder-specific phase values of a cylinder.

15. The method as claimed in claim 10, wherein the internal combustion engine has a reference cylinder with a cylinder pressure sensor, the method also comprising: detecting a pressure value for the reference cylinder; determining the combustion profile parameter value for the reference cylinder based on the pressure value; determining the cylinder-specific phase value both for the reference cylinder and for a further cylinder; and determining the combustion profile parameter value for the further cylinder based on the combustion profile parameter value for the reference cylinder, the phase value for the reference cylinder, the phase value for the further cylinder and the stored transfer function.

16. The method as claimed in claim 15, further comprising: calculating a difference between the value of the transfer function for the phase value of the further cylinder and the value of the transfer function for the phase value of the reference cylinder, wherein the combustion profile parameter value for the further cylinder is determined by adding the combustion profile parameter value for the reference cylinder and the calculated difference.

17. The method as claimed in claim 10, wherein the cylinder-specific combustion profile parameter value is a burnt fuel mass fraction MFBxx.

18. The method as claimed in claim 17, wherein the burnt fuel mass fraction MFBxx is an MFB50 value.

19. A computer program which, when executed by a processor, is designed to carry out the method as claimed in claim 1.

Description

DESCRIPTION OF DRAWINGS

[0036] FIG. 1 shows a relationship between the tooth time and the crank angle with three tooth time intervals.

[0037] FIG. 2 shows a phase spectrum determined for a tooth time interval in FIG. 1.

[0038] FIG. 3 shows a series of measured phase values for the determination of an offset correction value for a cylinder.

[0039] FIG. 4 shows a representation of measured phase values and combustion profile parameter values for determining a transfer function.

[0040] FIG. 5 shows a comparison between actual combustion profile parameter values and determined combustion profile parameter values.

[0041] Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

[0042] According to the disclosure, a toothed encoder signal is detected by a crankshaft position sensor and a toothed encoder wheel (e.g., a 60-2 toothed encoder wheel) mounted on the crankshaft and a corresponding tooth time interval is determined from this for each cylinder.

[0043] FIG. 1 shows a corresponding relationship between a tooth time Zz (μs/°) and a crank angle KW (°) with three tooth time intervals 1, 2A, 2B, 3 according to one example. The depiction corresponds to three revolutions of a three-cylinder engine. The first tooth time interval 1 (or crank angle interval) begins at the start of the expansion phase at TDC1, i.e. the top dead center ignition for cylinder 1 (corresponding to a crank angle KW equal to 0°) in cycle n, and ends when the top dead center TDC2 (corresponding to a crank angle KW equal to 240°) for the following (second) cylinder is reached. This is followed immediately by the second tooth time interval, which in the illustration consists of a part 2A in cycle n (crank angle KW between 240° and 360°) and a part 2B in the previous cycle n−1 (crank angle KW between −360° and −240°). In the illustration in FIG. 1, the third tooth time interval 3 lies immediately before the first tooth time interval 1, i.e. between TDC3 (KW equals −240°) and TDC1 (KW equals 0°) in cycle n−1. For the present three-cylinder engine, there is an associated tooth time interval with a length of 240° crank angle for each cylinder and for each work cycle. The tooth time interval is determined in the engine control while the engine is in operation.

[0044] A Fourier transformation is then carried out for the tooth time interval assigned to each working cycle of a cylinder. As a result of the transformation, amplitude and phase information is obtained for each integral multiple of the fundamental frequency (first harmonic frequency).

[0045] FIG. 2 shows a phase spectrum determined according to the disclosure for a tooth time interval in FIG. 1, for example, for the part of the toothed encoder signal which corresponds to the tooth time interval 3. The phase value P1 corresponds to the fundamental frequency or the first harmonic frequency, the phase value P2 corresponds to the second harmonic frequency, and the phase value P3 corresponds to the third harmonic frequency.

[0046] According to the disclosure, the phase information of the first harmonic frequency, i.e. the value P1 in FIG. 2, is used to determine the MBxx combustion parameters. This phase information or this phase value is generally designated PHI.sub.cy1=i_n for cylinder i and combustion cycle n. The desired combustion profile parameter value, e.g. MFB50, can now be determined on the basis of the phase value and a stored transfer function.

[0047] An offset correction is carried out first to improve the precision. For this purpose, the internal combustion engine is operated at an approximately constant engine speed without combustion, e.g. in the overrun phase. This results in cylinder- and speed-dependent values for PHI.sub.cy1=i_n, which are referred to below as PHI.sub.cy1=i_n_motorized.

[0048] The values PHI.sub.cy1=i_n_motorized are different from zero due to tolerances in the crankshaft signal detection and in the 60-2 toothed encoder wheel and exhibit a statistical spread. This is shown in FIG. 3, which shows a measurement of phase values for cylinder 3 at an engine speed of 2000 rpm. The mean value MW (e.g., over approx. 100-200 cycles per cylinder) represents the systematic error in the determination of PHI.sub.cy1=i_n. The dashed lines MW+ and MW− show the corresponding standard deviation. The series of measured phase values shown in FIG. 3 can be used for the determination of an offset correction value for the cylinder.

[0049] The accuracy of the method is improved by correcting the values PHI.sub.cy1=i_n for this systematic offset error. The offset correction value is typically determined once per driving cycle via the engine control device. The corrected phase values are denoted as PHI.sub.cy1=i_n adapted and are determined as follows:

[00001]$PH{I}_{\mathrm{cyl}=i\_n\mathrm{\_adapted}}={\mathrm{PHI}}_{\mathrm{cyl}=i\_n}-\frac{1}{\mathrm{number}\mathrm{of}\mathrm{cycles}}{\Sigma }_{n=1}^{\mathrm{number}\mathrm{of}\mathrm{cycles}}{\mathrm{PHI}}_{\mathrm{cyl}=i\_n\_\mathrm{motorized}}$

[0050] The abovementioned transfer function is stored in the engine control device and is generally determined in the laboratory (for the respective engine type). FIG. 4 shows a representation of phase values measured (in the laboratory) and combustion profile parameter values for determining a transfer function according to the disclosure, such as the transfer function f_PHI_MBF50, which can be used to determine the combustion profile parameter value MBF50 from determined phase information.

[0051] For the calibration of the method according to the disclosure, a representative vehicle is used in the development process. Alternatively, an engine can also be used on an engine test bench if it can be ensured that the drive train dynamics correspond to the dynamics in the vehicle. Each cylinder of the engine is equipped with a reference cylinder pressure measurement (e.g. Kistler sensor). The reference MFB50 values are determined during calibration (MFBxx.sub.cy1=i_n_Kaitb) using a commercial indexing system such as AVL Indiset. Under steady-state engine conditions, approx. 200 combustion cycles per cylinder are recorded using the indexing system. In other words: MFBxx.sub.cy1=i_n_Kalib=Reference MFBxx from Indiset for cylinder i and combustion cycle n.

[0052] In addition to the values of MFB_xx.sub.cy1=i_n_Kalib, the values of PHI.sub.cy1=i_n are also recorded for the calibration.

[0053] The calibration process includes the following engine conditions: [0054] (a) Steady-state load and speed points at which the variables MFB_xx are to be detected during later operation of the vehicle. [0055] (b) For each load point from (a) a variation of the charge dilution in several steps. Depending on the application, [0056] (i) the external cooled EGR rate varies in several steps between EGR=0% and the maximum possible EGR rate or [0057] (ii) for homogeneous lean operation, the combustion lambda, starting from lambda=1, varies in several steps up to the maximum possible lambda. [0058] (c) For each load point from (a) and each dilution state from (b), the combustion characteristics MFBxx are varied by varying the ignition angle.

[0059] In addition, during the calibration, a drag measurement is carried out for each speed, as described above, and the values PHI.sub.cy1=i_n_adapted_Kalib are calculated using the offset correction on the basis of the recorded data.

[0060] In the next step, the recorded cycle-specific and cylinder-specific variables MFBxx.sub.cy1=i_n_Kalib and PHI.sub.cy1=i_n_adapted_Kalib are plotted against each other for each load point from (a) for the measurements from (b) and (c), as shown in FIG. 4.

[0061] The linear transfer function f_PHI_MFBxx can now be determined for each load point from (a) and the associated variations from (b) and (c) using a least square method. In FIG. 4, f_PHI MFB50 is shown as a solid line f.

[0062] According to the disclosure, this transfer function is now used to determine the combustion profile parameter value (for example, MFB50) based on the phase values PHI.sub.cy1=i_n_adapted which are determined and offset-corrected (as described above).

[0063] Thus, with the method according to the disclosure, the combustion profile parameter value can be determined precisely without using cost-increasing cylinder internal-pressure sensors:

MFBxx.sub.cy1=i_n=f_PHI_MFBxx(PHI.sub.cy1=i_n_adapted).

[0064] To reduce the cycle-to-cycle spread, it is advantageous to average the value over the number of M combustion cycles:

[00002]${\mathrm{MFBxx}}_{\mathrm{cyl}=i}=\frac{1}{M}{\Sigma }_{n=1}^M{\mathrm{MFBxx}}_{\mathrm{cyl}=i\_n}$

[0065] In a further example, a cylinder internal-pressure sensor can be installed in a single cylinder (reference cylinder) of the engine. The variable MFBxx.sub.Ref_n is determined using the pressure signal of the sensor and the combustion profile calculation in the engine control. Phase values are determined both for the reference cylinder and for a further cylinder (without an internal pressure sensor) and then the measured reference variable MFBxx.sub.Ref_n can be used to improve the determination of MFBxx.sub.cy1=i_n for each/the further cylinder which is not equipped with a cylinder internal-pressure sensor:

MFBxx.sub.cy1=i_n=MFBxx.sub.Ref_n+f_PHI_MFBxx(PHI.sub.cy1=i_n_adapted)−f_PHI_MFBxx(PHI.sub.Ref_n_adapted)

[0066] The spread (cycle to cycle) can also be reduced here by averaging.

[0067] FIG. 5 shows a comparison between actual combustion profile parameter values and combustion profile parameter values determined according to the disclosure. All the values are on, or in the immediate vicinity of the line L and thus indicate a very good match.

[0068] In summary, the present disclosure provides precise determination of combustion profile parameter values either entirely without cylinder internal-pressure sensors or with only one such sensor.

[0069] A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the disclosure. Accordingly, other implementations are within the scope of the following claims.

LIST OF REFERENCE DESIGNATIONS

[0070] 1 Tooth time interval [0071] 2A, 2B Tooth time interval [0072] 3 Tooth time interval [0073] Zz Tooth time [0074] KW Crank angle [0075] TDC1 Top dead center [0076] TDC2 Top dead center [0077] TDC3 Top dead center [0078] P Phase value [0079] P1 Phase value [0080] P2 Phase value [0081] P3 Phase value [0082] MFBxx xx % Mass fraction burned, burned mass fraction of fuel [0083] MW Mean value [0084] MW+ Standard deviation [0085] MW+ Standard deviation [0086] f Transfer function [0087] L Line