EP1068436B1 - Method for equalising the cylinders of a direct injection internal combustion engine - Google Patents

Description

The invention relates to a method for cylinder equalization in an internal combustion engine working with direct injection according to the preamble of claim 1.

In multi-cylinder, direct-injection internal combustion engines it occurs despite various interferences same control for high variances in mass flow between individual injectors. The different Fuel quantities lead to different torque contributions of the individual cylinders, which in addition to an increase in Uneven running due to speed fluctuations of the crankshaft too can lead to increased emissions.

DE 41 22 139 A1 describes a method for cylinder equalization regarding the fuel injection quantities at one Internal combustion engine known in which the spin each individual cylinder is detected. The individual measured values the spin are compared and at Deviations between the individual measured values are the Fuel injection quantities of the individual cylinders changed so that deviations are finally avoided and thus rotational irregularities the internal combustion engine can be eliminated.

The invention has for its object a method of Specify the type mentioned, with the simple and quick way of systematic failure of individual injectors the injection system with both stationary and even when the internal combustion engine is operating transiently can be.

The above object is achieved by the features of the claim 1 solved. Advantageous further developments are in the Subclaims specified.

The one released by the combustion in the individual cylinders Energy is converted into kinetic energy of the crankshaft. Express cylinder-specific combustion differences thus in fluctuations in speed from which an error is determined can be. This cylinder-specific error signal is characteristic of the systematic error during the injection process in the cylinder. In order even with transient operation the internal combustion engine, for example when accelerating Excluding misapplications becomes the characteristic Values, i.e. those recorded by the speed sensor Speed values, dynamically corrected with an acausal filter. This dynamic correction enables to determine an error even at speed transitions and a Adaptation to be carried out in the entire map area. Since that Process as an input variable for other control and regulation purposes anyway the control device of the internal combustion engine supplied crankshaft speed uses and therefore none additional hardware components are required a very inexpensive implementation to increase the Smooth running of the internal combustion engine.

Figur 1

den Drehzahlverlauf für fehlerfreie und fehlerbehaftete Injektoren im stationären Betrieb,

Figur 2

den Drehzahlverlauf für fehlerfreie Injektoren im stationären und instationären Betrieb,

Figur 3

den Drehzahlverlauf und die Mittelungszeitspannen für die dynamische Korrektur,

Figur 4

ein Diagramm zur Verdeutlichung der Laufzeit des Mittelwertfilters,

Figur 5

eine Darstellung der dynamischen Korrektur anhand eines Beschleunigungsvorganges und

Figur 6

Drehzahl- und Residuenverlauf bei leichter Beschleunigung der Brennkraftmaschine

An embodiment of the invention is explained below with reference to the drawing. Show it

Figure 1

the speed curve for faultless and faulty injectors in stationary operation,

Figure 2

the speed curve for error-free injectors in stationary and transient operation,

Figure 3

the speed curve and the averaging periods for the dynamic correction,

Figure 4

a diagram to illustrate the running time of the mean filter,

Figure 5

a representation of the dynamic correction based on an acceleration process and

Figure 6

Speed and residual curve with slight acceleration of the internal combustion engine

mit



mittleres Trägheitsmoment der Kurbelwelle

ω _{OT ( i )}

Winkelgeschwindigkeit im oberen Totpunkt (vor der Expansionsphase)

ω _{UT ( i )}

Winkelgeschwindigkeit im unteren Totpunkt (nach der Expansionsphase)

In order to be able to correct a possible deviation of the actually injected fuel quantity from the target injection quantity, it is necessary to determine a measure for this deviation, ie an error. The signal from a speed sensor is used for this. The energy released by the combustion in the individual cylinders is converted into kinetic energy of the crankshaft. Cylinder-specific combustion differences are expressed in speed fluctuations from which an error can be determined. The kinetic energy that is released in a cylinder i during combustion is calculated

With



average moment of inertia of the crankshaft

ω _{OT ( i )}

Angular velocity at top dead center (before the expansion phase)

ω _{UT ( i )}

Angular velocity at bottom dead center (after the expansion phase)

The bottom dead center (index UT) of the cylinder i corresponds to the top dead center (index OT) of the next ignited cylinder i +1. Therefore this equation can also be given as follows:

A positive change in kinetic energy (Δ E _kin (i)> 0) corresponds to a large injection quantity m _{B, i} corresponds to fuel and a negative change in kinetic energy (Δ E _kin (i) <0) is too small injection quantity m _{B, i} . If Δ E _kin ( i ) = 0, the correct amount of fuel has been injected.

However, these statements only apply if you are from a quasi-stationary Operating state can go out (the average speed remains constant) and the load torque does not jump having.

In Figure 1A, the course of the speed n over time t for faultless injectors, the speed curve in FIG. 1B over time for faulty injectors for each applied stationary operation of the internal combustion engine. In both cases are in the form of circles the individual cylinder Signal values, namely the speeds before the ignition n (OT (i)) and after ignition n (UT (i)) for cylinder i.

The angular velocity ω and thus also ΔE _kin can be calculated from the speed n by simple conversion.

The method is also used when the internal combustion engine cannot be in stationary operation Statements are made about the errors of the injectors. Becomes e.g. the engine is just accelerating, a Errors recognized where there may not be any.

This problem is shown in Figure 2. The time course of the speed in FIG. 2A was simulated with faultless injectors in stationary operation. The above-mentioned method provides a value for the change in the kinetic energy Δ E _kin ( i ) = 0, ie no error. In FIG. 2B, the internal combustion engine was accelerated using the same fault-free injectors. The method now calculates a value for the change in the kinetic energy ΔE _kin ( i )> 0 since the rotational speed after the combustion is greater than before and concludes that the current injector has a positive error, that is to say it is injecting too much.

The restriction of a quasi-steady state of operation to eliminate and also in dynamic speed transitions To be able to determine errors, one leads a dynamic one Correction of the speed by. This dynamic is explained Correction below using the example of a 4-cylinder internal combustion engine.

The basic idea behind dynamic correction is to take the tendency of the average speed into account. For this purpose, the actual speeds n _{OT ( i +1)} and n _{OT ( i ) are} not used to determine the error, but corrected speeds n and _{OT ( i +1)} and n and _{OT ( i )} .

These are freed from the trend of medium speed and leave thus a statement about the injection behavior of the considered Injector too.

Average speeds are calculated to determine this trend and related to the current values.

But to compare the current speed with an average To enable, the mean filter used have a group term of τ = 0. This is only through to achieve an acausal filter at which the current time lies in the middle of the averaging interval.

The averaging period should be as short as possible be to possible changes in the speed trend quickly recognizable. On the other hand, at least a working cycle to be averaged to the systematic Calculate errors in the injectors.

Since the internal combustion engine examined here is a 4-cylinder internal combustion engine, four speed values (in each case at top dead center) must be taken into account when reporting an operating cycle. However, in order to be able to maintain the required runtime of the mean value filter of τ = 0, the current point in time must be in the middle of the averaging interval, as described above. Since there is no mean value for four speed values, the mean is averaged over five values. The dynamic correction of the speed results from the acausal averaging: n OT ( i ) = 1 8th n OT ( i -2) + 1 4 n OT ( i -1) + 1 4 n OT ( i ) + 1 4 n OT ( i +1) + 1 8th n OT ( i +2) n _{TDC ( i -2)} and n _{TDC ( i + 2)} belong to the same cylinder and are weighted only half as much as the other three values. This guarantees notification of exactly one work cycle.

One can get a handle on the acausality by carrying out the calculation for the cylinder current at time i only at the end of the averaging period at time i + 2. Since the corresponding value is only needed again in the next work cycle, i.e. at time i + 4, this is possible without problems.

An average corresponding to equation (3) is also calculated for OT _{(i + 1)} : n OT ( i +1) = 1 8th n OT ( i -1) + 1 4 n OT (1) + 1 4 n OT ( i +1) + 1 4 n OT ( i +2) + 1 8th n OT ( i +3)

In Figure 3, the speed curve over two work cycles ASP and the averaging periods for n _{OT ( i +1)} and n _{OT ( i +1) is} shown graphically for dynamic correction.

To clarify the influence of the transit time τ of the mean filter, please refer to Figure 4. In Figure 4A is a Sinusoidal signal recorded. Below that (Figure 4B) is the course of the mean when averaging over a quarter of the period using a classic method with With the help of a causal mean filter, whose runtime τ> 0 is. To calculate the mean value for the current time (indicated here by a vertical straight line) only values from the past are used. It is clearly one Phase shift between sine signal and the middle one Curve (mean 1).

FIG. 4C shows the mean value curve when using a Acausal filter (τ = 0) can be seen. For the calculation used the same number of values from the past and the future (the current time is in the middle of the averaging interval). Here you can clearly see that the sine signal and the mean value signal 2 are in phase.

The corrected speeds are now calculated using the mean values from equations (3) and (4): n OT ( i +1) = n OT ( i +1) - n OT ( i +1) - n OT ( i ) 2 n OT ( i ) = n OT ( i ) - n OT ( i +1) - n OT ( i ) 2

The values n _{TDC (i)} and n _{TDC (i + 1)} denote the values measured with the aid of the speed sensor.

An example of dynamic speed correction is shown in FIG. Flawless injectors are assumed. This can be seen from the fact that the current speed values n _{TDC ( i )} and n _{TDC ( i +1)} and the associated mean values n _{OT ( i )} and n _{OT ( i +1) have} the same distances (here Δ n = 10). The internal combustion engine is accelerated. Surrender n OT ( i ) = 1220 [rpm] n OT ( i +1) = 1220 [rpm]

The corrected speeds are therefore the same size, from which it can be concluded that the injectors are working correctly. The rising trend of speed could thus be filtered out become.

nach folgender Gleichung berechnet:

und daraus ein Residuum berechnet zu

mit Knorm = 12 ·· 2π60 Hu ·m Bmax ·100 und

R_z (i)

Residuum des Zylinders Z(i)

Θ

mittleres Trägheitsmoment der Kurbelwelle (appliziert)

H_u

unterer Heizwert für den verwendeten Kraftstoff

m_Bmax

maximal einspritzbare Kraftstoffmenge

n and_{OT ( i )}

korrigierte Drehzahl am oberen Totpunkt des Zylinders i

n and_{OT ( i +1)}

korrigierte Drehzahl am oberen Totpunkt des Zylinders i+1

K_norm

als Normierungsfaktor

das bei entsprechender Normierung eine Aussage darüber enthält, wieviel Prozent Kraftstoff zuviel oder zuwenig eingespritzt wurde.With the corrected speed values from equations (5) and (6), the change in the kinetic energy is now for the cylinder Z (i)

calculated according to the following equation:

and from that a residual is calculated

With K standard = 1 2 · ·  2π 60 H u · m B Max · 100 and

R _z ( i )

Residual of cylinder Z (i)

Θ

average moment of inertia of the crankshaft (applied)

H _u

lower calorific value for the fuel used

m _Bmax

maximum amount of fuel that can be injected

n and _{OT ( i )}

corrected speed at top dead center of the cylinder i

n and _{OT ( i +1)}

corrected speed at top dead center of cylinder i + 1

K _norm

as a standardization factor

which, with appropriate standardization, contains a statement as to what percentage of fuel was injected too much or too little.

In equation (8) the factor 2π / 60 is used to convert revolutions per minute (unit of n) to radians per second (unit of ω). Multiplying by 1/2 ·  gives an energy difference that corresponds to that in equation (2). The division by H _u · m _{B max} and the multiplication by 100 result in a percentage error since the difference in kinetic energy that occurs due to injector errors during ignition is related to the total energy of the injected fuel mass m _B.

FIG. 6 shows a speed curve with a slight acceleration the internal combustion engine shown in the Cylinder Z (1) specified a larger injection quantity of fuel has been. From the lower representation of Figure 6 sees one that, despite an increase in speed, the individual cylinder Residuals, synonymous with errors, due to remain the same as the specified dynamic correction. Everyone fourth value belongs to the same cylinder i. You can see clearly that the error patterns remain the same.

mit

als Initialisierung für einen multiplikativen Adaptionsfall.
Darin ist

δ_Z(i),k

Korrekturterm für Zylinder i nach Adaptionsschritt k

R_Z(i),k

Residuum des Zylinders i zum Adaptionsschritt k

α

positiver frei wählbarer Adaptionsparameter zwischen 0 und 1, der die Geschwindigkeit der Adaption festlegt

Proportional injection corrections can now be made from the cylinder-individual residuals obtained with this method. Since the residuals are only relative measures for the change in the amount of fuel to be injected, the adaptation algorithm is also created with this in mind. It must be ensured that the internal combustion engine does not receive more or less fuel at any time of correction than in the uncorrected case. The algorithm should therefore only take on the task of uniformly distributing the injection quantity. This results in the adaptation algorithm for a 4-cylinder internal combustion engine

With

as initialization for a multiplicative adaptation case.
In it

δ _{Z (i), k}

Correction term for cylinder i after adaptation step k

R _{Z (i), k}

Residual from cylinder i to adaptation step k

α

positive freely selectable adaptation parameter between 0 and 1, which determines the speed of the adaptation

If you inject more fuel into a cylinder (i.e. that Residual of the cylinder was positive) so this amount of fuel pro rata (i.e. one third at a time 4-cylinder internal combustion engine, generally 1 / (z-1) in one Internal combustion engine with z-cylinders) for the other cylinders deducted.

Injecting less fuel into a cylinder (i.e. the residual of the cylinder was negative) so this amount of fuel pro rata (i.e. one third each for a 4-cylinder internal combustion engine, generally 1 / (z-1) for one Internal combustion engine with z-cylinders) for the other cylinders draufgeschlagen.

This ensures that the torque during the Cylinder equality remains constant as the total amount of fuel to be supplied does not change.

The sum of the correction terms is the same at all times the number of cylinders.

To correct the injection quantity m _{B, i} into a cylinder, only a single control variable is available, namely the injection duration T _E. Because of the always positive slope of an inverted nozzle characteristic (injection quantity as a function of the injection duration), a longer actuation entails a larger injection quantity. The injection correction can thus be carried out directly over the injection duration by _ideally multiplying the correction terms δ _{Z ( i ), k} from the adaptation algorithm by the ideal injection times T _E specified by the engine control.

Claims (8)

1. Method for cylinder equalization with reference to the fuel injection quantities for an internal combustion engine operating by direct injection, in the case of which the fuel injection quantities can be controlled by changing the injection times, and cylinder-specific correction terms are applied to the injection times in such a way that the smooth running of the internal combustion engine is enhanced, characterized in that

   the speed (n) of the crankshaft of the internal combustion engine is detected both in the quasi-stationary and in the dynamic operating state of the internal combustion engine,

   the speed values (n) are corrected by means of a mean-value filter having an envelope delay (τ) of zero,

   the change in the kinetic energy ΔE_{kin , i} of the crankshaft in the expansion interval of a cylinder (i) is calculated from the corrected speed values (n and),

   there is derived therefrom for each cylinder (Z(i)) a relative measure, in particular the residue R_Z(i), which contains information on too much or too little injected fuel quantity and

   correction terms (δ_Z(i),k) for the injection time (TE) are calculated from this measure, in particular the residue R_Z(i).
2. Method according to Claim 1, characterized in that the correction of the speed values (n_(i)) is performed according to the following relationship: n OT ( i +1) = nOT ( i +1) - n OT(i+1) - n OT(i) 2 n OT ( i ) = nOT ( i ) - n OT(i+1) - n OT(i) 2

   n and _OT(i) , n and _OT(i+1)

   where is the corrected speed of the cylinder i and i+1, respectively, over a working cycle, and

   n _{OT ( i )}, n _{OT (i+1)}

   is the mean value of the speed of the cylinder i and i+1, respectively, over a working cycle.

3. Method according to Claim 2, characterized in that in the case of a 4-cylinder internal combustion engine the mean value n _OT(i) of the cylinder (i) is calculated as: n OT(i) = 18 nOT ( i -2) + 14 nOT ( i -1) + 14 nOT(i) + 14 nOT ( i +1) + 18 nOT ( i +2)
4. Method according to Claim 2, characterized in that in the case of a 4-cylinder internal combustion engine the mean value n _OT(i+1) of the cylinder (i+1) is calculated as: n OT(i+1) = 18 nOT ( i -1) + 14 nOT ( 1 ) + 14 n OT(i+1) + 14 nOT ( i +2) + 18 nOT ( i +3)
5. Method according to Claim 1, characterized in that the values for the change in the kinetic energy ΔE_{kin , i} are referred to a value which specifies the maximum fuel energy which can be fed in this interval, and the measure, in particular the residue R_Z(i), is calculated therefrom.
6. Method according to Claim 1, characterized in that the change in the kinetic energy ΔE_kin,Z(i) is calculated in accordance with the following equation ΔE_kin (i) = 1 / 2··(n and 2 / OT(i+1) - n and 2 / OT(i)) and the measure is determined therefrom as RZ ( i ) = Knorm ·( n 2 OT k,i+1 - n 2 OT k,i ) where

   Θ

   is the mean moment of inertia of the crankshaft,

   H_u

   is the lower calorific value for the fuel used,

   m_Bmax

   is the maximum injectable fuel quantity,

   n and_OT(i)

   is the corrected speed at the top dead centre of the cylinder i,

   n and_{OT ( i+1 )}

   is the corrected speed at the top dead centre of the cylinder i+1, and

   K_norm

   is a normalizing factor which has the value of Θ2 ·1 Hum Bmax 2π60 .

7. Method according to Claim 1, characterized in that correction terms (δ_Z(i),k) by which the values for the injection times (T_E,ideal) are multiplied are calculated from the calculated measures.
8. Method according to Claim 7, characterized in that the correction terms δ_Z(i),k are calculated as

   

   with

   

   as initialization value, and where

   δ_Z(i),k

   is the correction term for cylinder i after adaptation step k,

   R_Z(i),k

   is the residue of the cylinder i relative to the adaptation step k, and

   α

   is a positive, freely selectable adaptation parameter between 0 and 1 which fixes the rate of the adaptation.

Images