JP5263185B2 - Air-fuel ratio estimation system - Google Patents

Description

  The present invention relates to an air-fuel ratio estimation system.

Conventionally, for example, in Patent Document 1, an in-cylinder pressure sensor is used to detect an in-cylinder pressure P between predetermined crank angles, and PV ^κ (κ is a specific heat ratio) from the detected in-cylinder pressure P and the in-cylinder volume V at the time of detection. ), And a method for estimating the air-fuel ratio using the correlation between the calculated difference in PV ^κ and the calorific value Q in the combustion chamber is disclosed.

In the above method, the heat quantity Q _{air of the} intake air and the calorific value Q _fuel due to the combustion of the supplied _fuel are used instead of the mass of the intake air and the supplied fuel necessary for calculating the air-fuel ratio. The calorific value Q _air and the calorific value Q _fuel are estimated based on PV ^κ based on the knowledge that the change pattern of the calorific value Q with respect to a predetermined crank angle and the change pattern of PV ^κ with respect to the crank angle substantially coincide (similar). The Specifically, the amount of heat Q _air is estimated from the difference in PV ^κ between the crank angle when the intake valve is opened and the crank angle when the intake valve is closed. Similarly, the calorific value Q _fuel is estimated from the difference in PV ^κ between the crank angle at the time of ignition or ignition and the crank angle at the substantial end of combustion.

JP 2006-144643 A JP 2008-274811 A

However, in actual combustion, the difference in ignition timing and ignition timing affects the calorific value Q _fuel due to combustion. FIG. 1 is a graph showing changes in PV [kJ] with respect to the crank angle θ. Solid lines (a) to (c) shown in FIG. 1 respectively show changes in PV with respect to the crank angle θ for three different combinations of ignition timing and air-fuel ratio. Specifically, the solid line (a) is when the ignition timing MBT and the air / fuel ratio are controlled to 14.6, and (b) is the ignition timing MBT−10 ° (retard) and the air / fuel ratio is controlled to 14.6. (C) corresponds to the case where the ignition timing MBT and the air-fuel ratio are controlled to 19, respectively. PV is calculated based on the actually measured in-cylinder pressure P. Further, the crank angle θ = 0 ° corresponds to the compression top dead center, and the region where the crank angle θ shows a negative value than 0 ° has a positive value before 0 ° before the compression top dead center (BTDC). The area shown corresponds to after compression top dead center (ATDC).

As shown by the solid line (b) in FIG. 1, when ignition is performed at MBT-10 °, the PV peak arrival timing is delayed from the solid line (a) by the amount by which the ignition timing is retarded. In addition, the PV peak value itself is larger than that of the solid line (a). As the PV peak value increases, the calorific value Q _fuel similar to the PV change pattern also increases. From this, it can be seen that when the ignition timing is changed, the heat generation amount Q _fuel changes.

  On the other hand, as shown by the solid line (c) in FIG. 1, when the air-fuel ratio is controlled at 19, the PV peak is reached almost simultaneously with the case of the solid line (a) where the air-fuel ratio is controlled at 14. However, the PV of the solid line (b) has a peak value larger than the PV of the solid line (a). This is because when the air-fuel ratio is controlled at 19, the intake air amount becomes larger than when the air-fuel ratio is controlled at 14.6, so that the intake air has a high pressure (assuming that the combustion injection amount is constant). . From this, it can be seen that the peak value of PV increases as the compression ratio of the intake air increases.

From the above, the calorific value Q _fuel due to combustion changes depending on the advance / retard control of the ignition timing and the engine load. For this reason, the method of estimating the air-fuel ratio using the calorific value due to combustion of the supplied fuel has a problem that the air-fuel ratio cannot be estimated with high accuracy, and there is still room for improvement.

  The present invention has been made to solve the above-described problems, and an object thereof is to provide an air-fuel ratio estimation system capable of estimating an air-fuel ratio with high accuracy.

In order to achieve the above object, a first invention is an air-fuel ratio estimation system,
In-cylinder pressure detecting means for detecting the in-cylinder pressure of the cylinder;
An in-cylinder temperature detecting means for detecting an in-cylinder temperature of the cylinder;
Intake air amount detection means for detecting the intake air amount of the internal combustion engine;
Parameter calculating means for calculating parameters relating to the composition of the combustion gas in the cylinder according to the state equation of the gas, using the values of the cylinder pressure and the cylinder temperature when the exhaust valve is opened;
Air-fuel ratio estimation means for estimating the air-fuel ratio based on the relationship between the intake air amount and the parameter for each cycle of the internal combustion engine;
It is characterized by providing.

The second invention is the first invention, wherein
The air-fuel ratio estimating means stores in advance a map showing the relationship between the parameter relating to the composition of the combustion gas and the air-fuel ratio for each intake air amount, and the calculated parameter and the detected intake air amount are stored in the map. The air-fuel ratio is estimated by collating.

The third invention is an air-fuel ratio estimation system for achieving the above object,
In-cylinder pressure detecting means for detecting the in-cylinder pressure of the cylinder;
An in-cylinder temperature detecting means for detecting an in-cylinder temperature of the cylinder;
Intake air amount detection means for detecting the intake air amount of the internal combustion engine;
An EGR passage connecting an exhaust passage and an intake passage of the internal combustion engine;
Exhaust gas amount acquisition means for acquiring an exhaust gas amount to be recirculated to the intake passage through the EGR passage;
Parameter calculating means for calculating parameters relating to the composition of the combustion gas in the cylinder according to the state equation of the gas, using the values of the cylinder pressure and the cylinder temperature when the exhaust valve is opened;
Air-fuel ratio estimating means for estimating the air-fuel ratio based on the relationship between the intake air amount and the exhaust gas amount and the parameter for each cycle of the internal combustion engine;
It is characterized by providing.

Moreover, 4th invention is set in 3rd invention,
The air-fuel ratio estimating means stores in advance a map showing the relationship between the parameter relating to the composition of the combustion gas and the air-fuel ratio for each intake air amount, the calculated parameter, the detected intake air amount, and the acquired The air-fuel ratio is estimated by comparing the exhaust gas amount with the map.

  According to the first and second inventions, the parameters relating to the composition of the combustion gas can be calculated by substituting the in-cylinder pressure and the in-cylinder temperature into the gas state equation established in the combustion chamber when the exhaust valve is opened. This parameter has a correlation with the air-fuel ratio. Therefore, the air-fuel ratio can be estimated with high accuracy.

  When the exhaust gas is recirculated into the intake passage, the value of the parameter related to the composition of the combustion gas at the exhaust valve opening timing changes by the amount of the exhaust gas. According to the third and fourth inventions, it is possible to correct the exhaust gas. Therefore, even when the exhaust gas is recirculated, the air-fuel ratio can be estimated with high accuracy.

It is the figure which showed the change of PV [kJ] with respect to crank angle (theta). 2 is a diagram for describing a system configuration according to Embodiment 1. FIG. FIG. 5 is a diagram showing the relationship between n · R and the air-fuel ratio at the exhaust valve opening timing when the intake air amount is constant. In Embodiment 1, it is a figure which shows the flow of the process performed by the arithmetic processing unit. FIG. 6 is a diagram showing a relationship between n · R at an exhaust valve opening timing and an air-fuel ratio when there is an external EGR. In Embodiment 2, it is a figure which shows the flow of the process performed by the arithmetic processing unit.

Embodiment 1 FIG.
Hereinafter, Embodiment 1 of the present invention will be described with reference to FIGS. 2 to 4.

[Description of system configuration]
FIG. 2 is a diagram for explaining a system configuration according to the first embodiment of the present invention. As shown in FIG. 2, the system of this embodiment includes an internal combustion engine (hereinafter simply referred to as “engine”) 10. The engine 10 is a spark ignition type 4-stroke reciprocating engine provided with a spark plug 12. Further, it is also an in-cylinder direct injection engine provided with a direct fuel injection type injector 14 that directly injects fuel into the cylinder. Although only one cylinder is shown in FIG. 2, a general vehicle engine is composed of a plurality of cylinders.

  A crank angle sensor 16 that outputs a signal CA every time the crankshaft rotates by a predetermined rotation angle is attached to the engine 10. From the signal CA of the crank angle sensor 16, the crank angle θ (rotational position of the crankshaft), the engine speed NE, the in-cylinder volume V that is geometrically determined by the crank angle θ, and the like can be calculated.

  Further, an in-cylinder pressure sensor 18 for measuring the in-cylinder pressure P is attached to at least one cylinder of the engine 10. An air flow meter 20 for detecting an intake air amount Ga flowing through the intake passage is provided at the inlet of the intake passage connected to the cylinder. A throttle 22 for detecting the throttle opening degree TA is provided downstream of the air flow meter 20.

  An intake valve 24 and an exhaust valve 26 are provided on the cylinder head of the engine 10. The intake valve 24 and the exhaust valve 26 are configured such that valve opening characteristics can be changed by a variable valve mechanism (not shown). An exhaust temperature sensor 28 for measuring the temperature of the exhaust gas is attached to the exhaust port near the exhaust valve 26.

  Further, the system of the present embodiment includes an arithmetic processing device 50. The arithmetic processing unit 50 processes signals from the crank angle sensor 16, the in-cylinder pressure sensor 18, the air flow meter 20, the exhaust temperature sensor 28, and the like, and the processing results are used as a spark plug 12, an injector 14, a throttle 22, and a variable valve mechanism. This is reflected in the operation of the actuator.

  As described above, the amount of heat generated by the combustion of the supplied fuel varies depending on the advance / retard angle control of the ignition timing and the engine load. For this reason, in the first embodiment, the air-fuel ratio is estimated according to the gas state equation using the output values of the in-cylinder pressure sensor 18 and the exhaust gas temperature sensor 28. That is, according to the first embodiment, the air-fuel ratio can be obtained without using the amount of heat generated by the combustion of the supplied fuel. Further, the air-fuel ratio can be obtained without using an air-fuel ratio sensor. In addition, since the responsiveness of the in-cylinder pressure sensor and the temperature sensor is higher than the responsiveness of the air-fuel ratio sensor, precise air-fuel ratio control can be performed immediately after starting. Therefore, according to the first embodiment, an improvement in exhaust emission can be expected.

The gas equation of state is expressed by the following equation (1).
P ・ V = n ・ R ・ T (1)
Assuming that the gas (exhaust gas) in the combustion chamber after combustion follows the above equation (1), the following equation (2) is established at the exhaust valve opening timing (EVO).
P _EVO · V _EVO = n · R · Tex (R is a constant)
・ N ・ R = P _EVO・ V _EVO / Tex (2)

Therefore, if the cylinder pressure P _EVO , cylinder volume V _EVO, and cylinder temperature Tex at the exhaust valve opening timing are applied to the right side of the equation (2), n · R of the exhaust valve opening timing can be obtained. As described above, the in-cylinder volume V _EVO is geometrically determined by the crank angle θ. Therefore, if the in-cylinder pressure P _EVO and the in-cylinder temperature Tex are applied, the exhaust valve opening timing n · R can be obtained.

Here, since the exhaust gas is a combustion gas in the combustion chamber, the following equation (3) is established for n · R at the exhaust valve opening timing.
n · R = n _{O 2} · R _{O 2} + n _{CO 2} · R _{CO 2} + (3)
From equation (3), it can be seen that n · R is a value that varies depending on the composition of the exhaust gas at the exhaust valve opening timing. Further, it can be seen that n · R is a value that varies depending on the intake air and the supplied fuel. Therefore, it can be seen that n · R has a correlation with the air-fuel ratio. From the above, the air-fuel ratio can be calculated by applying the in-cylinder pressure P _EVO and the in-cylinder temperature Tex.

  Incidentally, n · R varies depending on the engine load. FIG. 3 is a diagram showing the relationship between n · R at the exhaust valve opening timing and the air-fuel ratio when the intake air amount is constant. As shown in FIG. 3, when the load factor KL is 20% to 30%, the value of n · R at the exhaust valve opening timing increases. Here, since the load factor KL correlates with the amount of air actually taken into the cylinder per cycle, the load factor KL also correlates with the compression ratio. If the value of n · R at the exhaust valve opening timing changes, an accurate air-fuel ratio cannot be obtained even if n · R is calculated.

  Therefore, in the first embodiment, correction for the compression ratio is performed on n · R derived from the gas state equation. The air-fuel ratio is calculated based on the relationship between the correction value and the air-fuel ratio.

The relationship of the following equation (4) is established between n · R and the air / fuel ratio in consideration of the compression ratio correction.
A / F = [{(A + F) / A} −1] ⁻¹ ∝ [{P _EVO · V _EVO / (Tex · Mair) −1}] ⁻¹ (4)
In the equation (4), “Mair” is the mass of fresh air detected by the air flow meter 20. A value calculated by a known method (for example, an in-cylinder DJ method) may be used as the mail. It is assumed that the relationship between n · R taking into account the compression ratio correction and the air-fuel ratio is created in advance as a map by experiments, simulations, etc., and stored in advance in the arithmetic processing unit 50.

[Specific Processing in First Embodiment]
Next, the air-fuel ratio calculation procedure executed by the arithmetic processing unit 50 will be described with reference to the flowchart of FIG.

In the routine shown in FIG. 4, first, when the exhaust valve is opened, the in-cylinder pressure P _EVO is detected (step 100). Specifically, the cylinder pressure sensor 18 detects the cylinder pressure P _EVO when the exhaust valve is opened. The in-cylinder pressure P _EVO is acquired at a timing when the crank angle θ = θ _EVO . As will be described later, it is desirable to use an average value of about five cycles for the in-cylinder pressure P _EVO in consideration of the responsiveness of the exhaust temperature sensor 28.

Simultaneously with the detection of the in-cylinder pressure P _EVO , the in-cylinder temperature Tex is detected (step 102). Here, specifically, the exhaust temperature sensor 28 detects the in-cylinder temperature Tex when the exhaust valve is opened. Since the exhaust temperature sensor 28 has a heat capacity, it is desirable to use an average value of about 5 cycles in consideration of responsiveness. Further, an air mass Mail is calculated (step 104). Here, specifically, the Air calculated based on the intake air amount Ga detected by the air flow meter 20 is read.

Subsequently, the air-fuel ratio is calculated from P _EVO · V _EVO / Tex (step 106). Here, specifically, various data detected or read in steps 100 to 104 are substituted into [{P _EVO · V _EVO / (Tex · Mair) −1}] ⁻¹ . Then, a search is made from a map stored in advance in the arithmetic processing unit 50 using the air-fuel ratio corresponding to the obtained value as a key. Thereby, an air fuel ratio can be calculated | required.

  As described above, according to the routine shown in FIG. 4, it is possible to correct an air-fuel ratio error resulting from a difference in ignition timing or compression ratio. Therefore, the air-fuel ratio can be estimated with high accuracy.

In the first embodiment described above, the in-cylinder pressure sensor 18 is the “in-cylinder pressure detection means” in the first invention, and the exhaust temperature sensor 28 is the “in-cylinder temperature acquisition means” in the first invention. The air flow meter 20 corresponds to the “intake air amount detection means” in the first invention. In step 106, the arithmetic processing unit 50 substitutes the various data detected or read in steps 100 to 104 into [{P _EVO · V _EVO / (Tex · Mair) −1}] ⁻¹ . As a result, the “parameter calculation means” in the first invention searches in the map stored in advance in the arithmetic processing unit 50 using the air-fuel ratio corresponding to the obtained value as a key in the above step 106. The “air-fuel ratio estimation means” in the first aspect of the invention is realized.

  In the first embodiment, the exhaust temperature sensor 28 is provided in the exhaust port, but the exhaust temperature sensor 28 may be provided directly in the cylinder. In addition, a known means capable of measuring the temperature in the combustion chamber at the exhaust valve opening timing can be used in place of the exhaust temperature sensor 28. Further, the engine to which the present invention is applied is not limited to the in-cylinder direct injection engine as in the first embodiment. The present invention can also be applied to a port injection type engine. Further, the present invention can be applied not only to a spark ignition type engine but also to a compression self-ignition type engine.

Embodiment 2. FIG.
Next, a second embodiment of the present invention will be described with reference to FIGS.
The second embodiment is characterized in that a routine shown in FIG. 6 to be described later is executed on the assumption that an external EGR system is added to the system shown in FIG. Since the external EGR system itself is a known system, description of its configuration and the like is omitted.

[Air-fuel ratio estimation considering external EGR]
When an external EGR system is installed, the intake air amount only needs to take into account fresh air that has passed through the air flow meter 20. However, when there is an external EGR, exhaust gas flows into the fuel chamber and the total gas amount increases, so it is necessary to consider the external EGR as well.

  FIG. 5 is a diagram showing the relationship between n · R at the exhaust valve opening timing and the air-fuel ratio when there is an external EGR. As shown in FIG. 5, when there is an external EGR, the value of n · R at the exhaust valve opening timing increases by the amount of the exhaust gas. If the value of n · R at the exhaust valve opening timing rises, an accurate air-fuel ratio cannot be obtained even if n · R is calculated. Therefore, in the second embodiment, correction for the external EGR is performed on n · R derived from the gas state equation. The air-fuel ratio is calculated based on the relationship between the correction value and the air-fuel ratio.

The relationship of the following equation (5) is established between n · R taking into account the external EGR and the air-fuel ratio.
A / F = [{(A + F) / A} −1] ⁻¹ ∝ [[{(P _EVO · V _EVO / Tex) −K × EGR + OFS} / Mair] −1] ^{−1 −1} (5)
In Equation (5), the term K × EGR is a correction term related to the EGR rate, and OFS is a term related to the primary correlation.

[Specific Processing of Embodiment 2]
Next, the air-fuel ratio calculation procedure executed by the arithmetic processing unit 50 will be described with reference to the flowchart of FIG.

In the routine shown in FIG. 6, as in FIG. 4 of the first embodiment, first, the in-cylinder pressure P _EVO is detected when the exhaust valve is opened (step 100). Next, the in-cylinder temperature Tex is detected simultaneously with the detection of the in-cylinder pressure P _EVO (step 102). Further, an air mass Mail is calculated (step 104).

Subsequently, the EGR rate is calculated (step 108). Here, for example, it is calculated from the combustion speed, specific heat ratio, and EGR valve opening map. Subsequently, the air-fuel ratio is calculated from P _EVO · V _EVO / Tex (step 110). Here, specifically, various data detected or read out in steps 100 to 104 and 108 are represented by [[{(P _EVO · V _EVO / Tex) −K × EGR + OFS} / Mair] −1] ⁻¹ . Assigned. Then, a search is made from a map stored in advance in the arithmetic processing unit 50 using the air-fuel ratio corresponding to the obtained value as a key. Thereby, an air fuel ratio can be calculated | required.

  As described above, according to the routine shown in FIG. 6, the air-fuel ratio error resulting from the introduction of the external EGR can be corrected. Therefore, even when the external EGR system is applied, the air-fuel ratio can be estimated with high accuracy.

In the second embodiment described above, the in-cylinder pressure sensor 18 is the “in-cylinder pressure detecting means” in the third invention, and the exhaust temperature sensor 28 is the “in-cylinder temperature acquiring means” in the third invention. The air flow meter 20 corresponds to the “intake air amount detection means” in the third aspect of the invention. In addition, in the above step 106, the arithmetic processing unit 50 converts the various data detected or read out in steps 100 to 104 into [[{(P _EVO · V _EVO / Tex) −K × EGR + OFS} / Mair] −1. By substituting ⁻¹ , the “parameter calculating means” in the third aspect of the invention is stored in advance in the arithmetic processing unit 50 using the air-fuel ratio corresponding to the value obtained in step 110 as a key. By searching from the map, the “air-fuel ratio estimating means” in the third aspect of the present invention is realized.

DESCRIPTION OF SYMBOLS 10 Engine 18 In-cylinder pressure sensor 20 Air flow meter 28 Exhaust temperature sensor 50 Arithmetic processing unit

Claims (4)

In-cylinder pressure detecting means for detecting the in-cylinder pressure of the cylinder;
An in-cylinder temperature detecting means for detecting an in-cylinder temperature of the cylinder;
Intake air amount detection means for detecting the intake air amount of the internal combustion engine;
Parameter calculating means for calculating parameters relating to the composition of the combustion gas in the cylinder according to the state equation of the gas, using the values of the cylinder pressure and the cylinder temperature when the exhaust valve is opened;
Air-fuel ratio estimation means for estimating the air-fuel ratio based on the relationship between the intake air amount and the parameter for each cycle of the internal combustion engine;
An air-fuel ratio estimation system comprising:   The air-fuel ratio estimating means stores in advance a map showing the relationship between the parameter relating to the composition of the combustion gas and the air-fuel ratio for each intake air amount, and the calculated parameter and the detected intake air amount are stored in the map. The air-fuel ratio estimation system according to claim 1, wherein the air-fuel ratio is estimated by collating. In-cylinder pressure detecting means for detecting the in-cylinder pressure of the cylinder;
An in-cylinder temperature detecting means for detecting an in-cylinder temperature of the cylinder;
Intake air amount detection means for detecting the intake air amount of the internal combustion engine;
An EGR passage connecting an exhaust passage and an intake passage of the internal combustion engine;
Exhaust gas amount acquisition means for acquiring an exhaust gas amount to be recirculated to the intake passage through the EGR passage;
Parameter calculating means for calculating parameters relating to the composition of the combustion gas in the cylinder according to the state equation of the gas, using the values of the cylinder pressure and the cylinder temperature when the exhaust valve is opened;
Air-fuel ratio estimating means for estimating the air-fuel ratio based on the relationship between the intake air amount and the exhaust gas amount and the parameter for each cycle of the internal combustion engine;
An air-fuel ratio estimation system comprising:   The air-fuel ratio estimating means stores in advance a map showing the relationship between the parameter relating to the composition of the combustion gas and the air-fuel ratio for each intake air amount, the calculated parameter, the detected intake air amount, and the acquired 4. The air-fuel ratio estimation system according to claim 3, wherein the air-fuel ratio is estimated by comparing an exhaust gas amount with the map.

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