JP2006189013A - Internal EGR state estimation method for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To estimate an internal EGR amount and an internal EGR rate with high accuracy.
A method for estimating an internal EGR state of an internal combustion engine provided with a variable valve timing mechanism, wherein a basic index of an internal EGR state is obtained based on a valve overlap amount of an intake / exhaust valve and a rotational speed of the internal combustion engine. Next, the valve overlap center phase at which the internal EGR amount is minimized is obtained as the minimum EGR center phase based on the valve overlap amount and the engine speed, and then the actual center phase of the valve overlap of the intake valve and the exhaust valve is determined. The internal index is estimated by correcting the basic index according to the deviation from the minimum EGR center phase.
[Selection] Figure 1

Description

  The present invention estimates the internal EGR state estimation for estimating the flow rate (EGR amount) of internal EGR gas flowing into the combustion chamber again from the exhaust valve or the intake valve among the gases burned in the combustion chamber, or the ratio (EGR rate) to fresh air. Regarding the method.

Conventionally, a variable valve timing mechanism (so-called VVT: Variable Valve Timing mechanism) that can change the opening / closing timing of an intake valve (or an intake valve) and an exhaust valve (or an exhaust valve) of an internal combustion engine (engine) is widely known. ing.
With such a variable valve timing mechanism, the valve opening / closing timing of the intake valve or exhaust valve is changed according to the operating state of the engine. It is sometimes possible to change the valve opening / closing timing with emphasis on output characteristics.

  By the way, the combustion gas (exhaust gas) of the engine is discharged to the exhaust port through the exhaust valve. However, not all exhaust gas is discharged from the combustion chamber, but a part of the exhaust gas flows backward from the exhaust port through the exhaust valve. Or once discharged to the intake port and then flows into the combustion chamber along with fresh air. This occurs when the exhaust valve closing timing is after top dead center, or when the intake valve opening timing is before top dead center. Of these, the gas flowing again into the cylinder (combustion chamber) is generally referred to as internal EGR.

  Various methods for estimating the internal EGR amount have been proposed. The internal EGR amount depends on the period during which both the intake valve and the exhaust valve are open (hereinafter referred to as valve overlap). Therefore, in an engine having a VVT mechanism in which the valve overlap is changed, the valve overlap is an important parameter for estimating the internal EGR amount.

As a method for estimating the internal EGR amount, for example, a basic value of the internal EGR amount without valve overlap is calculated, and when the valve overlaps, the overlap time and its center crank angle are taken into consideration. A technique is known in which the amount of increase correction calculated in this way is added to the basic value to calculate the internal EGR amount (see Patent Document 1).
Here, regarding this increase correction, specifically, when the exhaust valve closing timing is before exhaust top dead center, a basic correction value is set corresponding to the overlap time, and this basic correction value is set as the correction amount. Is done. When the exhaust valve closing timing is after the exhaust top dead center, a value (decrease correction value) proportional to the retard amount from the exhaust top dead center at the closing timing is calculated, and the decrease correction is calculated from the basic correction value. A value obtained by subtracting the value is set as the correction amount.
JP 2001-221105 A

  However, in this conventional technology, since only the relationship between the exhaust valve closing timing and top dead center is focused on the exhaust valve closing timing as a reference, an estimation that accurately corresponds to the change in the engine operating state is made. It was difficult to do. That is, the center crank angle is an intermediate crank angle between the opening timing of the intake valve and the closing timing of the exhaust valve. However, in this technique, the opening timing of the intake valve is not taken into consideration. Incorrect crank angle.

In particular, in the case of an engine having a VVT mechanism on the intake valve side, the valve opening timing of the intake valve is appropriately changed according to the operating state. Therefore, the correction is made only by the valve closing timing of the exhaust valve as described above. Even if the value is set, the exact center crank angle cannot be obtained.
Therefore, the conventional technique has a problem that the engine equipped with the VVT mechanism cannot estimate the internal EGR amount and the internal EGR rate with high accuracy.

  The present invention has been devised in view of such problems, and an object of the present invention is to provide an internal EGR state estimation method for an internal combustion engine that can estimate an internal EGR amount and an internal EGR rate with high accuracy.

  Therefore, the internal EGR state estimation method for an internal combustion engine according to the present invention is an internal EGR state estimation method for an internal combustion engine in which a valve timing variable mechanism capable of changing the opening / closing timing of each of the intake valve and the exhaust valve is provided. An internal EGR basic index derivation step for obtaining a basic index of the internal EGR state of the internal combustion engine based on the valve overlap state of the intake valve and the exhaust valve and the rotational speed of the internal combustion engine, and the valve overlap state And a minimum center phase derivation step for obtaining a valve overlap center phase that minimizes the amount of internal EGR based on the rotational speed as a minimum EGR center phase, and an actual center phase of valve overlap of the intake valve and the exhaust valve, A phase deviation deriving step for obtaining a deviation from the minimum EGR center phase, and the above in accordance with the deviation It is characterized by having an internal EGR condition estimation step of estimating an internal EGR condition by correcting this indication (claim 1).

In the internal EGR state estimation step, the basic index is corrected with a quadratic approximate characteristic with respect to the deviation (claim 2).
Further, the basic index is corrected according to an exhaust temperature corresponding correction value obtained based on the engine speed and the intake air amount (Claim 3).
Further, the basic index is corrected according to an exhaust pressure corresponding correction value obtained on the basis of the engine speed and the intake air amount (Claim 4).

The basic index is corrected in accordance with a correction value obtained based on the intake pressure and the exhaust pressure (claim 5).

In the internal EGR state estimation method for an internal combustion engine according to the present invention, the internal EGR state is estimated by correcting the basic index of the internal EGR in accordance with the valve overlap center phase, so the internal EGR state of the engine equipped with the variable valve timing mechanism Can be obtained with high accuracy (claim 1).
Further, since the basic index is corrected by the quadratic approximate characteristic with respect to the deviation between the actual center phase of the valve overlap and the minimum EGR center phase, the internal EGR state can be obtained relatively easily. Therefore, the calculation logic can be simplified (claim 2).

Further, since the basic index is corrected in consideration of the exhaust gas temperature, the internal EGR state can be obtained with high accuracy.
Moreover, since the basic index is corrected in consideration of the exhaust pressure, the internal EGR state can be obtained with high accuracy.
Further, since the basic index is corrected in consideration of the intake pressure and the exhaust pressure, the internal EGR state can be obtained with high accuracy.

  Hereinafter, an internal EGR state estimation method for an internal combustion engine according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic block diagram showing an internal EGR state estimation device to which the present invention is applied, and FIG. FIG. 3 is a diagram showing a change in the internal EGR amount with respect to the valve overlap center phase, FIG. 3 is a diagram showing characteristics of the valve lift, and FIG. 4 is a flowchart for specifically explaining the internal EGR state estimation method.

  First, an internal EGR state estimation device will be described. This device is an apparatus attached to an internal combustion engine (engine) for estimating the internal EGR rate and / or the internal EGR amount of the engine, and is mainly shown in FIG. As described above, the ECU (controller) 100 is configured. Hereinafter, the internal EGR rate and the internal EGR amount are collectively referred to as an internal EGR state, and the internal EGR is also simply referred to as EGR.

  As shown in FIG. 1, the ECU 100 includes an internal EGR basic index deriving unit 1 that obtains a basic index of an internal EGR state, and an exhaust temperature corresponding correction value that sets a correction value k1 corresponding to the exhaust temperature for the basic index. A setting unit 2, an exhaust pressure corresponding correction value setting unit 3 for setting a correction value k2 corresponding to the exhaust pressure (hereinafter simply referred to as exhaust pressure) with respect to the basic index, and a response to the intake pressure with respect to the basic index The correction value setting unit 4 corresponding to the intake pressure for setting the correction value k3 and the correction value setting unit 5 for VOL center phase for setting the correction value k4 corresponding to the center phase of the valve overlap (VOL) with respect to the basic index. Is provided.

In this internal EGR state estimation apparatus, as shown in the following equation (1), the basic index Q0 set by the internal EGR basic index deriving unit 1 is multiplied by the correction values k1 to k4, respectively. Thus, the final internal EGR amount Q2 is calculated.
Q2 = k1, k2, k3, k4, Q0 (1)
When the internal EGR amount Q2 is calculated in this way, the internal EGR rate R2 is calculated by the following equation (2) based on the fresh air amount Qa.
R2 = (Q2 / Qa) · 100 (2)
More specifically, the ECU 100 includes an engine speed sensor that detects the engine speed Ne, an air flow sensor (AFS) that detects the intake air amount, an intake pressure sensor that detects the intake air flow rate, and the like. Are connected, and information from these sensors is input to the ECU 100.

The intake flow rate information from the AFS is converted into volumetric efficiency Ev and used as load information. Further, in this embodiment, the intake pressure uses the pressure in the intake manifold manifold (intake manifold). For this reason, the intake pressure is hereinafter referred to as intake manifold pressure or simply manifold pressure.
By the way, this engine is provided with a variable valve timing mechanism (hereinafter, VVT mechanism) that can change the opening and closing timings of the intake valve (intake valve) and the exhaust valve (exhaust valve) (not shown). This VVT mechanism is composed of an intake side VVT mechanism that can change the opening / closing timing of the intake valve, and an exhaust side VVT mechanism that can change the opening / closing timing of the exhaust valve, and these intake side and exhaust side VVT mechanisms. Are configured to be independently controllable.

  In the present embodiment, each VVT mechanism is configured to be able to continuously change the valve opening timing and the valve closing timing without changing the valve opening / closing period. Specifically, the cam angle phase can be retarded or advanced with respect to the crank angle, so that the shape of the valve lift characteristic line can be obtained as shown in FIG. The phase of the valve lift characteristic between the intake side and the exhaust side is changed without changing the value.

Therefore, when the VVT mechanism operates, the valve overlap (refer to VOL: IO to EC in FIG. 3) and the phase with respect to the top dead center (TDC) of the valve overlap VOL center (hereinafter referred to as VOL center phase). VOL center reference) is changed.
In FIG. 3, EO is the opening timing of the exhaust valve, EC is the closing timing of the exhaust valve, IO is the opening timing of the intake valve, and IC is the closing timing of the intake valve. Further, since such a VVT mechanism itself is already a known technique, a detailed description of the structure of the VVT mechanism is omitted.

The operation of the VVT mechanism is executed based on a control signal from a VVT mechanism control unit (not shown) in the ECU 100, and the operation of the actuator of the VVT mechanism is performed based on such a control signal. By being controlled, the operating characteristics of the intake valve and the exhaust valve are changed.
In addition, the VVT mechanism control unit feeds back information such as the opening timing (IO, EO) or closing timing (IC, EC) of the intake valve and the exhaust valve, and the VVT mechanism control unit. Then, the valve overlap and the VOL center phase are calculated from these pieces of information. The valve overlap and the VOL center phase are collectively referred to as an overlap state.

In this apparatus, the estimated value of the internal EGR state is corrected according to such a VOL center phase. Details of this point will be described later.
Next, the internal EGR state estimation method will be described. First, in the internal EGR basic index derivation unit 1 of the ECU 100, a basic EGR amount (basic index) Q0 is set based on the engine speed Ne and the valve overlap VOL. .

The internal EGR basic index deriving unit 1 stores a two-dimensional map using the engine speed Ne and the valve overlap VOL as parameters, and from this map, an estimated value of the internal EGR amount in the current engine operating state is stored. A basic basic EGR amount Q0 is set.
Here, the map stored in the internal EGR basic index deriving unit 1 is basically set to such a characteristic that the internal EGR amount increases as the valve overlap increases. In other words, exhaust gas is discharged to the exhaust port during the exhaust stroke, but if the exhaust valve is closed after top dead center, the exhaust gas is discharged from the exhaust port at the initial stage of the subsequent intake stroke due to negative pressure in the cylinder (combustion chamber). If the intake valve is opened before the top dead center, the exhaust gas discharged to the intake port side in the latter half of the exhaust stroke is returned to the cylinder again in the intake stroke. Because it will be. Such a reflux amount generally increases as the valve overlap increases. Therefore, the characteristic is set such that the internal EGR amount increases as the valve overlap increases.

In this map, the characteristic is set such that the internal EGR amount decreases as the engine speed Ne increases. This is because as the engine speed Ne increases, the time during which the intake negative pressure acts on the exhaust gas staying in the exhaust port is shortened, and it becomes difficult to obtain the reflux due to inertia.
Next, in the exhaust gas temperature correction value setting unit 2, a correction value (exhaust gas temperature correction value) k1 corresponding to the exhaust gas temperature is set. In the present embodiment, the exhaust temperature is estimated using the engine speed Ne and the volumetric efficiency (load) Ev as parameters, and the exhaust temperature corresponding correction value k1 is set according to the estimated exhaust temperature. It is set up.

That is, the exhaust gas temperature correction value setting unit 2 is provided with a two-dimensional map using the engine speed Ne and the volumetric efficiency (load) Ev as parameters. The exhaust gas temperature and the exhaust gas temperature correction value are included in this map. k1 is stored. The correction value k1 is set from the engine speed Ne and the volumetric efficiency (load) Ev.
Here, since the exhaust density generally decreases as the exhaust temperature becomes higher, the amount of EGR flowing into the cylinder from the exhaust side decreases. In view of this, in the exhaust gas temperature correction value setting unit 2, a two-dimensional map is basically set such that the correction value k1 decreases as the exhaust gas temperature increases. Note that a temperature sensor may be provided on the exhaust path to directly detect the exhaust temperature.

  Next, in the exhaust pressure corresponding correction value setting unit 3, a correction value (exhaust pressure corresponding correction value) k2 corresponding to the exhaust pressure is set. The exhaust pressure corresponding correction value setting unit 3 is provided with a map for determining the exhaust pressure from the engine speed Ne and the volumetric efficiency Ev, similar to the exhaust temperature corresponding correction value setting unit 2 described above. A correction value k2 corresponding to the pressure and the exhaust pressure is set.

Further, the exhaust pressure corresponding correction value setting unit 3 is set to a characteristic in which the correction value k2 increases as the exhaust pressure increases. This is because the amount of exhaust gas flowing backward from the exhaust port into the cylinder increases as the exhaust pressure increases. Note that a pressure sensor may be provided on the exhaust path to directly detect the exhaust pressure.
Next, in the intake pressure corresponding correction value setting unit 4, a correction value (intake pressure corresponding correction value) k3 corresponding to the manifold pressure (intake pressure) is set.

Here, as shown in FIG. 1, the intake pressure corresponding correction value setting unit 4 includes a first correction unit 4a that sets a manifold pressure correction value k _3a from the manifold pressure and the exhaust pressure, and the manifold pressure correction value k _3a . And a second correction unit 4b for setting a correction value _k3b . Also, this is the first correction portion 4a and two-dimensional map that stores a correction value k _3a corresponding to the Mani pressure and exhaust pressure are stored, the correction value k based from the map, Mani pressure and exhaust pressure _3a is read out. In addition, the value obtained in the said exhaust pressure corresponding | compatible correction value setting part 3 is applied for an exhaust pressure.

The second correction unit 4b stores a two-dimensional map that stores correction values k3b corresponding to the engine speed and valve overlap. Similar to the first correction unit 4a, the second correction unit 4b stores the correction value k3b. The correction value k _3b is read based on the Ne pressure and the valve overlap VOL.
The intake pressure corresponding correction value setting unit 4 sets an intake pressure corresponding correction value k3 from these correction values k _3a and k _3b based on the following equation.
k3 = k _3a・ k _3b +1
When the correction values k1, k2, and k3 are set in this way, a value obtained by multiplying the basic EGR amount Q0 set by the internal EGR basic index deriving unit 1 by these correction values is calculated. The Here, this value is Q1 (= Q0 · k1 · k2 · k3).

  Next, the VOL center phase correspondence correction value setting unit 5 that is a main part of the present apparatus will be described. As described above, the VOL center phase correspondence correction value setting unit 5 corresponds to the center phase of the valve overlap VOL. A correction value (VOL center phase correspondence correction value) k4 is set, and the final estimated value Q2 of the internal EGR is calculated by multiplying the correction value k4 by Q1.

Here, the necessity of setting the correction value k4 corresponding to the center phase of such valve overlap VOL will be described.
As described above, the internal EGR basic index deriving unit 1 obtains the basic EGR amount using the valve overlap VOL as a parameter, but does not consider the VOL center phase at all. The map used in the internal EGR basic index deriving unit 1 represents the basic EGR amount when the VOL center phase = 0 ° BTDC.

  On the other hand, FIG. 2 shows the internal EGR amount when the engine speed Ne and the valve overlap VOL are both kept constant (for example, Ne = 1500 rpm, VOL = 40 °) and only the VOL center phase is changed. It is the figure calculated | required experimentally. In FIG. 2, A on the horizontal axis is the VOL center phase at which the internal EGR amount is minimum, X1 is the VOL center phase (= 0 ° BTDC) in the basic EGR map, and X2 is the actual VOL center phase. The vertical axis indicates the ratio of the VOL center phase (minimum EGR center phase) A to the internal EGR amount where the internal EGR amount is minimum.

As shown in FIG. 2, it can be seen that even if the valve overlap is the same, the internal EGR amount varies greatly depending on the VOL center phase. Further, as shown, the internal EGR amount has a quadratic curve characteristic with respect to the VOL center phase.
The quadratic approximate curve can be expressed by the following equation.
Y = K (X−A) ² +1 (K and A are constants)
Therefore, the characteristics (K, A) of the quadratic approximate curve as shown in FIG. 2 are stored in advance, a correction value k4 corresponding to the valve overlap is obtained from the quadratic approximate curve, and based on this correction value k4. Thus, the internal EGR amount is estimated with high accuracy.

  For this reason, the VOL center phase corresponding correction value setting unit 5 includes a minimum center phase setting unit 6 for obtaining a VOL center phase (hereinafter referred to as a minimum EGR center phase) A that minimizes the internal EGR amount, and an actual center of valve overlap. A phase deviation calculator 7 for obtaining a deviation between the phase and the minimum EGR center phase, and a secondary approximation coefficient setting for setting a secondary approximation coefficient K to correct the basic EGR amount with a quadratic approximation characteristic for this deviation. And a basic EGR amount ratio setting unit 9 for setting a ratio Y1 to the basic EGR amount at a VOL center phase of 0 °.

In each of these parts, the constants K and A of the above-mentioned quadratic approximate curve equation are identified, and by substituting the current valve overlap for X, the ratio Y to the EGR amount at the minimum EGR phase A is It is calculated.
Hereinafter, each part will be described in detail. The minimum center phase setting unit 6 determines a VOL center phase A (see A in FIG. 2) that minimizes the internal EGR amount in the current valve overlap VOL. The minimum EGR center phase A is stored in advance as a two-dimensional map of the valve overlap VOL and the engine speed Ne, and is read from the map according to the engine speed Ne and the valve overlap VOL. .

When the minimum center phase setting unit 6 sets the minimum EGR center phase A, the phase deviation calculation unit 7 calculates the deviation between the valve overlap actual center phase X2 and the minimum EGR center phase A. Is done. The actual center phase X2 of the valve overlap is calculated by the above-described VVT mechanism control unit (not shown). Thereafter, the calculated deviation is squared and (X2-A) ² is output.

On the other hand, the secondary approximation coefficient setting unit 8 sets a secondary approximation coefficient K. Here, the secondary approximation coefficient K is stored in advance as a two-dimensional map of the valve overlap VOL and the engine speed Ne, and is read from the map according to the engine speed Ne and the valve overlap VOL. Yes.
Then, such a quadratic approximation coefficient K is multiplied by the square of the above-described deviation, and 1 is added to obtain K (X2-A) ² + 1 = Y2 (actual EGR amount ratio). .

Next, the basic EGR amount ratio setting unit 9 sets a ratio (basic EGR amount ratio) Y1 to the basic EGR amount at the VOL center phase of 0 °. Here, as shown in FIG. 2, the basic EGR amount ratio Y1 is an EGR amount ratio at the point X1 (VOL phase center = 0 °). If the above-described K and A are obtained, the above-mentioned second order approximation is performed. It can be obtained by substituting X1 (= 0 °) into the equation.
Therefore, the basic EGR amount ratio setting unit 9 obtains K and A once based on the engine speed Ne and the valve overlap VOL, and the basic EGR amount in the same procedure as when the actual EGR amount ratio Y2 is calculated. The ratio Y1 is calculated. Since X1 is always a point where the phase is 0 °, the basic EGR amount ratio Y1 may be mapped in the same manner as the constants K and A using the engine speed Ne and the valve overlap VOL as parameters. Good. Then, a value (Y2 / Y1) obtained by dividing the actual EGR amount ratio Y2 by the basic EGR amount ratio Y1 is calculated as the correction value k4.

Here, the reason why the correction value k4 is calculated in this way will be briefly described. As can be seen from FIG. 2, the actual EGR amount ratio Y2 described above is the internal EGR amount (= 1.0) in the minimum EGR center phase A. ) And not the ratio of the internal EGR amount at the point X1.
On the other hand, in the map of the internal EGR basic index deriving unit 1, the basic EGR amount Q0 is set as the EGR amount at the point X1 (VOL phase center = 0 °).

Therefore, in order to perform correction corresponding to the overlap center phase, it is necessary to calculate the ratio of the actual EGR amount to the EGR amount at the point X1. Then, by multiplying this value by the basic EGR amount as the correction value k4, it is possible to estimate an accurate EGR amount that also considers the phase center of the valve overlap.
For this reason, the VOL center phase correspondence correction value setting unit 5 calculates Y2 / Y1 (= k4), thereby the ratio of the internal EGR amount at the Y2 point to the basic EGR amount at the X1 point, that is, at the X1 point. The ratio of the current actual EGR amount when the basic EGR amount is set to 1 can be obtained, and by multiplying this by the basic EGR amount, the internal EGR amount considering the variation of the phase center of the valve overlap by the VVT mechanism can be obtained. Estimation is possible.

Further, the ECU 100 is provided with an internal EGR rate calculation unit 10, and the internal EGR rate calculation unit 10 divides the estimated internal EGR amount Q2 by the fresh air amount Qa and expresses the value as a percentage. An internal EGR rate is calculated.
Further, as shown in the figure, the ECU 100 is provided with basic ignition timing setting means 21 for setting the basic ignition timing of the engine and ignition timing correction amount setting means 22 for setting a correction amount for the basic ignition timing.

  Among these, the basic ignition timing setting means 21 sets the basic ignition timing according to the engine speed Ne and the volumetric efficiency (load) Ev. The ignition timing correction amount setting means 22 calculates the ignition timing correction amount according to the internal EGR rate calculated by the internal EGR rate calculation unit 10, the engine speed Ne, and the volumetric efficiency (load) Ev. A value obtained by adding the ignition timing correction amount to the basic ignition timing is output as the final ignition timing.

Next, the internal EGR state estimation method of the present invention will be described with reference to the flowchart of FIG. First, in step S10, the engine speed Ne, load (volumetric efficiency) Ev, valve overlap VOL, intake manifold pressure, VOL center phase, and the like are read.
Thereafter, the process proceeds to step S20, and an internal EGR amount (basic EGR amount; internal EGR basic index) Q0 is estimated from the map of the internal EGR basic index deriving unit 1 according to the engine speed Ne and the load Ev. In this map, the amount of internal EGR when VOL center phase = 0 ° is mapped (internal EGR basic index derivation step).

  Further, in step S30, the exhaust gas temperature correction value k1 is read from the map in the exhaust gas temperature correction value setting unit 2 in accordance with the engine speed Ne and the load Ev (exhaust gas temperature correction value derivation step), and the subsequent steps. In S40, the exhaust pressure corresponding correction value k2 is read from the map in the exhaust pressure corresponding correction value setting unit 3 in accordance with the engine speed Ne and the load Ev (exhaust pressure corresponding correction value deriving step).

In the next step S50, the intake pressure corresponding correction value k3 is set based on the intake manifold pressure, the exhaust pressure, the engine speed Ne, and the valve overlap VOL. In this step S50, in detail, first, the correction value k _3a is read from the map of the first correction unit 4a of the intake pressure corresponding correction value setting unit 4 according to the intake manifold pressure and the exhaust pressure, and the second correction is performed. The correction value k _3b is read from the map of the unit 4b according to the engine speed Ne and the valve overlap VOL. A value obtained by adding 1 to the product of these correction values k _3a and k _3b is set as k3.

Next, in step S60, the basic EGR amount Q1 is corrected using the correction values k1 to k3, thereby calculating the EGR amount (EGR amount at the point X1 in FIG. 2) Q1 at the VOL center phase 0 °. . That is, here, the EGR amount at the point X1 is estimated by the following equation.
Q1 = Q0 ・ k1 ・ k2 ・ k3
In step S70, the minimum center phase setting unit 6 sets the valve overlap VOL center phase (minimum EGR center phase) so that the internal EGR amount is minimized at the current valve overlap VOL and the engine speed Ne. A is set (minimum center phase deriving step).

Next, in step S80, a deviation (X2-A) between the current VOL center phase X2 and the minimum EGR center phase A is calculated (phase deviation derivation step).
In step S90, based on the above deviation, the current EGR amount ratio Y2 when the minimum EGR amount is set to 1 is calculated by the following equation.
Y2 = K (X2-A) ² −1
Next, in step S100, the ratio Y1 when the VOL center phase is X1 (= 0 °) is calculated by the following equation.
Y1 = K (X1-A) ² −1 = KA ² −1
In step S110, the ratio Y2 / Y1 of Y2 with respect to Y1 is calculated, and this value is output as the VOL center phase correspondence correction value k4. In other words, the relationship between the VOL center phase and the EGR amount can be approximated by the characteristics of the quadratic equation as shown in FIG. 2, so that this quadratic approximation equation can be used to calculate the actual EGR amount Y1 at the VOL center phase of 0 °. The ratio of the EGR amount Y2 at the VOL center phase X2 is obtained, and this value is calculated as the correction value k4. In other words, the correction value k4 corresponding to the VOL center phase is a ratio of the actual EGR amount based on the internal EGR amount in the VOL center phase X1 (= 0 °).

Next, in step S120, the EGR amount Q1 at the point X1 is corrected by the following equation with the correction value k4 obtained in step S110, and the internal EGR amount Q2 is calculated.
Q2 = Q1 · k4 = = Q0 · k1 · k2 · k3 · k4
In step S130, the internal EGR rate is calculated from the estimated internal EGR amount. In addition, the said step S90-step S130 function as an internal EGR state estimation process.

  As described above in detail, according to the internal EGR state estimation method for an internal combustion engine of the present invention, the correction value k4 corresponding to the center phase of the valve overlap is set, and the correction value k4 is set according to the valve overlap and the engine speed Ne. By correcting the basic EGR amount set by the above correction value k4, the internal EGR state can be estimated in consideration of the center phase of the valve overlap, thereby estimating the internal EGR state with high accuracy. Can do.

Further, since the basic EGR amount is corrected by the quadratic approximate characteristic with respect to the deviation between the actual center phase X2 of the valve overlap and the minimum EGR center phase A, the internal EGR state can be obtained relatively easily. The calculation logic inside can also be simplified.
Further, since the basic EGR amount is corrected in consideration of the exhaust temperature, the intake pressure, the exhaust pressure, etc., the internal EGR state can be obtained with higher accuracy.

  In addition, this invention is not limited to the above-mentioned embodiment, A various change is possible in the range which does not deviate from the meaning of this invention. For example, the secondary approximation coefficient setting unit 8 and the minimum center phase setting unit 6 may be combined into one map. That is, since the secondary approximation coefficient K and the minimum EGR center phase A are uniquely determined when the engine speed Ne and the valve overlap VOL are obtained, these values may be stored in one map as parameters. .

In addition, in the exhaust temperature corresponding correction value setting unit 2 and the exhaust pressure corresponding correction value setting unit 3, the correction values k1 and k2 are set using the engine speed Ne and the volumetric efficiency (load) Ev as parameters. The temperature corresponding correction value setting unit 2 and the exhaust pressure corresponding correction value setting unit 3 may be configured as one map.
In this embodiment, the case where the VVT mechanism is provided on both the intake side and the exhaust side has been described. However, the VVT mechanism may be provided on at least one of the intake side and the exhaust side. In the above description, a case where a VVT mechanism of a type that can change the phase of the valve lift characteristic line without changing the valve lift amount is applied as the VVT mechanism. However, if at least the valve overlap can be changed, Other types of VVT mechanisms may be applied.

It is a typical block diagram which shows the EGR state estimation apparatus to which the internal EGR state estimation method of the internal combustion engine concerning one Embodiment of this invention is applied. It is a figure for demonstrating the internal EGR state estimation method of the internal combustion engine concerning one Embodiment of this invention, Comprising: It is a figure which shows the relationship between the center phase of valve overlap, and EGR amount. It is a figure for demonstrating the internal EGR state estimation method of the internal combustion engine concerning one Embodiment of this invention, Comprising: It is a figure which shows the characteristic of a valve lift. 3 is a flowchart for specifically explaining an internal EGR state estimation method for an internal combustion engine according to an embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal EGR basic index derivation part 2 Exhaust temperature corresponding correction value setting part 3 Exhaust pressure corresponding correction value setting part 4 Intake pressure corresponding correction value setting part 5 VOL center phase corresponding correction value setting part 6 Minimum center phase setting part 7 Phase deviation calculation Unit 8 Secondary approximation coefficient setting unit 9 Basic EGR amount ratio setting unit 10 Internal EGR rate calculation unit

Claims (5)

An internal EGR state estimation method for an internal combustion engine provided with a variable valve timing mechanism capable of changing the opening and closing timing of each of an intake valve and an exhaust valve,
An internal EGR basic index derivation step for obtaining a basic index of the internal EGR state of the internal combustion engine based on the valve overlap state of the intake valve and the exhaust valve and the rotational speed of the internal combustion engine;
A minimum center phase derivation step for obtaining a valve overlap center phase at which the internal EGR rate is minimized based on the valve overlap state and the rotational speed as a minimum EGR center phase;
A phase deviation derivation step for obtaining a deviation between the actual center phase of the valve overlap of the intake valve and the exhaust valve and the minimum EGR center phase;
An internal EGR state estimation method for an internal combustion engine, comprising: an internal EGR state estimation step of correcting the basic index according to the deviation and estimating an internal EGR state. 2. The internal EGR state estimation method for an internal combustion engine according to claim 1, wherein in the internal EGR state estimation step, the basic index is corrected with a quadratic approximate characteristic with respect to the deviation. 2. The internal EGR state estimation method for an internal combustion engine according to claim 1, wherein the basic index is corrected in accordance with an exhaust temperature correspondence correction value obtained based on an engine speed and an intake air amount. 2. The internal EGR state estimation method for an internal combustion engine according to claim 1, wherein the basic index is corrected in accordance with an exhaust pressure corresponding correction value obtained based on an engine speed and an intake air amount. 2. The internal EGR state estimation method for an internal combustion engine according to claim 1, wherein the basic index is corrected according to a correction value obtained based on an intake pressure and an exhaust pressure.

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