JP3617058B2 - COMBUSTION STATE EVALUATION METHOD, COMBUSTION STATE EVALUATION DEVICE, AND COMBUSTION STATE CONTROL DEVICE FOR INTERNAL COMBUSTION ENGINE - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a method for evaluating a combustion state including a lean combustion limit of an internal combustion engine (engine), an apparatus for carrying out the method, and a combustion state control device for an internal combustion engine using such a combustion state evaluation method.
[0002]
[Prior art]
In general, when the air-fuel ratio of the air-fuel mixture supplied to the engine is leaned (lean) and lean burned, the amount of NOx generated in this lean combustion region is as shown in FIG. It is known to drop significantly. Therefore, from the viewpoint of NOx reduction, it is effective to operate the engine with the set air-fuel ratio further on the lean limit side.
[0003]
Accordingly, various lean burn engines that perform lean combustion by making the air-fuel ratio leaner as described above have been proposed with the aim of achieving both improved fuel consumption and reduced NOx.
In such a lean burn engine, air-fuel ratio feedback control is generally performed using a linear air-fuel ratio sensor (LAFS).
[0004]
[Problems to be solved by the invention]
However, in the above-described lean burn engine, the target air-fuel ratio is set to be about 1 to 2 richer than the lean limit in consideration of engine and sensor variations or environmental factors. There is room for further improvement in terms of reduction and NOx reduction.
[0005]
By the way, as a method for knowing the lean limit, it is only necessary to detect engine output torque fluctuations and cylinder misfire conditions. For example, as the former example, in-cylinder pressures corresponding to five different crank angles (combustion chamber) Pressure), and the engine output torque fluctuation is obtained from these in-cylinder pressures (see Japanese Patent Laid-Open No. 2-67446). In the latter case, two in-cylinder pressures during the compression stroke are used. The pressure sensor offset component is obtained from the pressure component, and the explosion stroke pressure information is obtained from the offset component and the in-cylinder pressure during the explosion stroke. When the explosion stroke pressure information is equal to or less than a predetermined value, it is determined that the cylinder is misfired. (See Japanese Patent Laid-Open No. 4-104033).
[0006]
However, in the former example (refer to Japanese Patent Laid-Open No. 2-67446), many (five points) in-cylinder pressures must be detected, and calculation for zero point calibration of the detected in-cylinder pressure is required. There is a problem of becoming.
In the latter example (see Japanese Patent Laid-Open No. Hei 4-104033), it is only necessary to detect a small in-cylinder pressure, but the calculation for zero point calibration and the gain of the detected in-cylinder pressure are detected. There is a problem that management is necessary.
[0007]
The present invention has been devised in view of such problems. A combustion index defined by using a small amount of detected in-cylinder pressure is created, and the combustion state of the internal combustion engine can be simplified using this combustion index. An object of the present invention is to provide a combustion state evaluation method and apparatus for an internal combustion engine that can be evaluated.
In addition, the present invention provides a combustion state control for an internal combustion engine that can control the combustion state of the internal combustion engine by controlling the combustion fluctuation adjusting element of the internal combustion engine using the above-described combustion state evaluation method.Method andAn object is to provide an apparatus.
[0008]
[Means for Solving the Problems]
Therefore, the combustion state evaluation method for an internal combustion engine of the present invention(Claim 1)Consists of the following steps:
(1)Can operate near the lean burn limitDetecting a combustion chamber pressure at three points, ie, a first combustion chamber pressure and a second combustion chamber pressure at two different points in the compression stroke of the internal combustion engine, and a third combustion chamber pressure in the internal combustion engine expansion stroke;
(2) Combustion index defined by the ratio between the difference between the third combustion chamber pressure and one of the first and second combustion chamber pressures and the difference between the first and second combustion chamber pressures. The step of calculating
(3) This combustion indexWhen is below the specified value, Internal combustion engineIs over the lean burn limitStep to evaluate.
[0009]
Also, the combustion state evaluation apparatus for an internal combustion engine of the present invention(Claim 2)IsAn internal combustion engine that can be operated near the lean combustion limit.After intake and exhaust valves are closedPressureThe first combustion chamber pressure during the compression stroke and the second combustion chamber pressure during the compression stroke of the internal combustion engine at a timing after the first combustion chamber pressure but before the ignition timing, and combustion is almost completed In-cylinder pressure detection means for detecting three pressures in the combustion chamber and the third combustion chamber pressure during the expansion stroke of the internal combustion engine at the time, and the third combustion chamber pressure and the second combustion detected by the in-cylinder pressure detection means Combustion index calculating means for calculating a combustion index defined by the ratio between the difference from the indoor pressure and the difference between the first and second combustion chamber pressures, and the combustion index calculated by the combustion index calculating meansWhen is below the specified value,TheInternal combustion engineIs over the lean burn limitIt is characterized by comprising evaluation means for evaluating.
[0010]
Furthermore, the combustion state control device for an internal combustion engine of the present invention(Claim 3)At least,Can operate near the lean burn limitIn-cylinder pressure detecting means for detecting three combustion chamber pressures, ie, a first combustion chamber pressure and a second combustion chamber pressure at two different points in the compression stroke of the internal combustion engine, and a third combustion chamber pressure in the internal combustion engine expansion stroke. And the difference between the third combustion chamber pressure detected by the in-cylinder pressure detecting means and the pressure in one combustion chamber of the first and second combustion chamber pressures, and the difference between the first and second combustion chamber pressures. Combustion index calculating means for calculating a combustion index defined by the ratio of the above, comparison means for comparing the combustion index calculated by the combustion index calculating means with a set value, and the comparing meansDeviation between the combustion index obtained in step 1 and the set valueOn the basis of the,In the direction that the magnitude of the deviation decreases,Control means for controlling combustion fluctuation adjusting element of internal combustion engineWhenIt is characterized by having been configured.
[0011]
Further, the combustion state control apparatus for an internal combustion engine according to the present invention (Claim 4) includes at least the first combustion chamber pressure and the second combustion at two different points in the compression stroke of the internal combustion engine that can be operated near the lean combustion limit. In-cylinder pressure detecting means for detecting three pressures in the combustion chamber, that is, the indoor pressure and the third combustion chamber pressure in the expansion stroke of the internal combustion engine, and the third combustion chamber pressure and the first pressure detected by the in-cylinder pressure detecting means , Combustion index calculation means for calculating a combustion index defined by the ratio of the difference between the pressure in the second combustion chamber and the pressure in one combustion chamber and the difference between the pressures in the first and second combustion chambers, and the calculation of the combustion index A comparison means for comparing the combustion index calculated by the means with a set value;Based on the accumulated information of the deviation between the combustion index and the set value obtained by the comparing means, the combustion fluctuation adjusting element of the internal combustion engine is controlled in a direction to decrease the magnitude of the accumulated information.It is characterized by comprising control means.
The control means preferably has a function of a conversion means for giving a dead zone and a weight to a deviation between the combustion index obtained by the comparison means and the set value (Claim 5).
[0012]
Further, as the combustion fluctuation adjusting element, for example, an air-fuel ratio adjusting element of an internal combustion engine can be considered.(Claim 6).
Further, the combustion state control method for an internal combustion engine according to the present invention (Claim 7) provides the first combustion chamber pressure and the second combustion chamber pressure at two different points in the compression stroke of the internal combustion engine that can be operated near the lean combustion limit. And the third combustion chamber pressure in the expansion stroke of the internal combustion engine are detected, and then the difference between the third combustion chamber pressure and one of the first and second combustion chamber pressures is detected. And calculating a combustion index defined by a ratio of the difference between the first and second combustion chamber pressures, comparing the combustion index with a set value, and based on a deviation between the combustion index and the set value, It is characterized in that the combustion fluctuation adjusting element of the internal combustion engine is controlled in a direction in which the magnitude of the deviation decreases.
Also, the combustion state control method for an internal combustion engine according to the present invention (Claim 8) provides the first combustion chamber pressure and the second combustion chamber pressure at two different points in the compression stroke of the internal combustion engine that can be operated near the lean combustion limit. And the third combustion chamber pressure in the expansion stroke of the internal combustion engine are detected, and then the difference between the third combustion chamber pressure and one of the first and second combustion chamber pressures is detected. And calculating a combustion index defined by a ratio of the difference between the first and second combustion chamber pressures, comparing the combustion index with a set value, and accumulating a deviation between the combustion index and the set value. Based on the information, the combustion fluctuation adjusting element of the internal combustion engine is controlled in a direction in which the size of the accumulated information decreases.
An internal combustion engine combustion state control device according to the present invention (Claim 9) includes a combustion state evaluation device for an internal combustion engine according to Claim 2 and an evaluation result of the evaluation means in the combustion state evaluation device. It is characterized by comprising control means for controlling the combustion fluctuation adjusting element of the internal combustion engine.
[0013]
[Action]
Combustion state evaluation method for internal combustion engine of the present invention described above(Claim 1)First of all,Can operate near the lean burn limitThe pressure in the combustion chamber at three points, that is, the pressure in the first combustion chamber and the pressure in the second combustion chamber at two different points in the compression stroke of the internal combustion engine and the pressure in the third combustion chamber in the expansion stroke of the internal combustion engine is detected. Calculating a combustion index defined by the ratio between the difference between the third combustion chamber pressure and one of the first and second combustion chamber pressures and the difference between the first and second combustion chamber pressures; This combustion indicatorWhen is below the specified value, Internal combustion engineIs over the lean burn limitevaluate.
[0014]
Also, the combustion state evaluation apparatus for an internal combustion engine of the present invention(Claim 2)In the cylinder pressure detection means,An internal combustion engine that can be operated near the lean combustion limit.The first combustion chamber pressure and the second combustion chamber pressure during the compression stroke are detected, and the third combustion chamber pressure during the internal combustion engine expansion stroke is detected. Next, the combustion index defined by the ratio between the difference between the third combustion chamber pressure and the second combustion chamber pressure detected by the in-cylinder pressure detecting means and the difference between the first and second combustion chamber pressures is burned. Combustion index calculated by the index calculation means and then calculated by the combustion index calculation means by the evaluation meansWhen is below the specified value, Internal combustion engineIs over the lean burn limitevaluate.
[0015]
Furthermore, the combustion state control device for an internal combustion engine of the present invention(Claim 3)In the cylinder pressure detection means,Can operate near the lean burn limitThe pressure in the combustion chamber at three points of the pressure in the first combustion chamber and the pressure in the second combustion chamber at two different points in the compression stroke of the internal combustion engine and the pressure in the third combustion chamber in the expansion stroke of the internal combustion engine is detected. The difference between the pressure in the third combustion chamber detected by the cylinder pressure detection means and the pressure in one combustion chamber of the first and second combustion chambers and the pressure in the first and second combustion chambers are detected by the index calculation means. The combustion index defined by the ratio to the difference is calculated, and the comparison means compares the combustion index calculated by the combustion index calculation means with the set value, and then the control means compares the combustion index.Deviation between the combustion index obtained in step 1 and the set valueOn the basis of the,In the direction that the magnitude of the deviation decreases,Control of the combustion fluctuation adjusting element of the internal combustion engine is performed.
[0016]
In the combustion state control apparatus for an internal combustion engine according to the present invention (Claim 4), the in-cylinder pressure detection means detects the first combustion chamber pressure at two different points in the compression stroke of the internal combustion engine that can be operated near the lean combustion limit. And the third combustion chamber pressure of the second combustion chamber pressure and the third combustion chamber pressure in the expansion stroke of the internal combustion engine are detected, and then the third in-cylinder pressure detecting means detects the third pressure detected by the in-cylinder pressure detecting means. A combustion index defined by a ratio between the difference between the pressure in the combustion chamber and the pressure in one of the first and second combustion chambers and the difference between the pressures in the first and second combustion chambers is calculated. Then, after comparing the combustion index calculated by the combustion index calculating means with the set value, the control means determines the magnitude of the accumulated information based on the accumulated information of the deviation between the combustion index and the set value obtained by the comparing means. In the direction of decreasing It is performed to control the fluctuation adjustment element.
The control means functions as a conversion means for giving a dead zone and a weight to the deviation between the combustion index obtained by the comparison means and the set value.
The combustion fluctuation adjusting element is preferably an air-fuel ratio adjusting element of the internal combustion engine.
In the combustion state control method for an internal combustion engine according to the present invention (Claim 7), first, the first combustion chamber pressure and the second combustion at two different points in the compression stroke of the internal combustion engine that can be operated near the lean combustion limit. After detecting the three combustion chamber pressures of the indoor pressure and the third combustion chamber pressure in the expansion stroke of the internal combustion engine, the above-mentioned third combustion chamber pressure and one of the first and second combustion chamber pressures are And the combustion index defined by the ratio of the difference between the first and second combustion chamber pressures, the combustion index is compared with the set value, and the deviation is determined based on the deviation between the combustion index and the set value. The combustion fluctuation adjusting element of the internal combustion engine is controlled in a direction in which the magnitude of the engine decreases.
In the combustion state control method for an internal combustion engine according to the present invention (Claim 8), first, the first combustion chamber pressure and the second combustion at two different points in the compression stroke of the internal combustion engine that can be operated near the lean combustion limit. After detecting the three combustion chamber pressures of the indoor pressure and the third combustion chamber pressure in the expansion stroke of the internal combustion engine, the above-mentioned third combustion chamber pressure and one of the first and second combustion chamber pressures are And the combustion index defined by the ratio of the difference between the first and second combustion chamber pressures described above, and the combustion index is compared with the set value to obtain the accumulated information of the deviation between the combustion index and the set value. Based on this, the combustion fluctuation adjusting element of the internal combustion engine is controlled in a direction in which the size of the accumulated information decreases.
Further, in the combustion state control device for an internal combustion engine according to the present invention (Claim 9), the control means performs the combustion of the internal combustion engine based on the evaluation result of the evaluation means in the combustion state evaluation device for the internal combustion engine according to Claim 2. Control of the variation adjustment factor is performed.
[0017]
【Example】
Embodiments of the present invention will be described below with reference to the drawings. FIGS. 1 to 10 show an engine combustion state control device using an engine combustion state evaluation method as one embodiment of the present invention. Is a control block diagram, FIG. 2 is a schematic configuration diagram of an engine system equipped with this apparatus, FIGS. 3 to 6 are flowcharts for explaining the control procedure, and FIG. 7 is a pressure measurement point used for calculation of a combustion index. FIG. 8 is a diagram for explaining the relationship between the combustion fluctuation near the lean limit and the crank angle, FIG. 9 is a diagram for explaining the correlation between the combustion index near the lean limit and the engine output, and FIG. 10 is the combustion It is a figure explaining the relationship between a parameter | index, an engine output, and an engine speed.
[0018]
Now, the engine system having this apparatus is as shown in FIG. 2. In FIG. 2, the engine (internal combustion engine) EG has an intake passage 2 and an exhaust passage 3 that communicate with the combustion chamber 1, The communication between the passage 2 and the combustion chamber 1 is controlled by the intake valve 4, and the communication between the exhaust passage 3 and the combustion chamber 1 is controlled by the exhaust valve 5.
[0019]
Further, the intake passage 2 is provided with an air cleaner, a throttle valve (not shown) and an electromagnetic fuel injection valve (injector) 6 in order from the upstream side, and the exhaust passage 3 is provided in order from the upstream side. A catalytic converter for exhaust gas purification and a muffler (not shown) are provided. The intake passage 2 is provided with a surge tank 2a, and the injector 6 is provided at the intake port portion corresponding to each cylinder.
[0020]
Further, an exhaust gas recirculation passage (EGR passage) 7 is interposed between the intake passage 2 and the exhaust passage 3, and an electromagnetic EGR valve 8 is interposed in the EGR passage 7. . Reference numeral 18 denotes a spark plug.
Further, various sensors are provided to control the engine EG. First, an in-cylinder pressure sensor 17 for detecting a pressure in the combustion chamber 1 (in-cylinder pressure: combustion chamber pressure) is provided, and a crank angle sensor 15 for detecting a crank angle (the crank angle sensor 15 is an engine speed). (Which also serves as a rotation speed sensor for detecting).
[0021]
On the intake passage 2 side, an air flow sensor (intake air amount sensor) 9 for detecting the intake air amount from Karman vortex information, an intake air temperature sensor 10 for detecting the intake air temperature, and an atmospheric pressure are detected in the air cleaner disposed portion. An atmospheric pressure sensor 11 is provided, and a potentiometer type throttle sensor 12 for detecting the opening degree of the throttle valve is provided at a portion where the throttle valve is disposed.
[0022]
Furthermore, on the exhaust passage 3 side, the oxygen concentration (O₂Air-fuel ratio sensor 13 (hereinafter simply referred to as “O”)₂Sensor 13 ”).
As other sensors, a water temperature sensor 14 for detecting the engine coolant temperature and a TDC sensor (cylinder discrimination sensor) 16 for detecting the top dead center of the first cylinder (reference cylinder) are also provided.
[0023]
Detection signals from these sensors are input to an electronic control unit (ECU) 20, which includes a CPU, ROM, RAM, and appropriate input / output interfaces. When a detection signal from each of the above-described sensors is input to the CPU, a required calculation is performed by the CPU, and a fuel injection amount control signal (fuel amount control signal), an ignition timing control signal, EGR based on the calculation result Control signals are output to the injector 6, spark plug 18, and EGR valve 8, respectively.
[0024]
Now, paying attention to fuel injection control (air-fuel ratio control), the ECU 20 outputs a fuel injection amount control signal calculated by a method described later to the injector 6, and the fuel injection amount control signal causes the injector 6 to Injection time T_inj(= T_B× Kaf × K × (1 + Kfb) + Tacc)).
Where T_BIs the basic drive time, and this basic drive time T_BIs determined according to the intake air amount information per one rotation of the engine obtained from the air flow sensor 9 and the crank angle sensor 15.
[0025]
Kaf is an air-fuel ratio correction coefficient, and this air-fuel ratio correction coefficient Kaf is set according to engine load information obtained from the airflow sensor 9 or the like, and is set to a value smaller than “1” during lean operation. The
Kfb is a feedback correction coefficient, and this feedback correction coefficient Kfb is set based on a combustion index Cio described later.
[0026]
Tacc is an acceleration / deceleration correction time, and this acceleration / deceleration correction time Tacc is a time set according to the acceleration / deceleration state of the engine obtained from the throttle sensor 12.
K is another correction coefficient, and the correction coefficient K is set according to the atmospheric pressure correction coefficient set according to the atmospheric pressure obtained by the atmospheric pressure sensor 11 and the intake air temperature obtained by the intake air temperature sensor 10. An intake air temperature correction coefficient, an engine cold correction coefficient set according to the engine coolant temperature obtained by the water temperature sensor 14, and the like are conceivable.
[0027]
Next, a method for obtaining the feedback correction coefficient Kfb based on the combustion index Cio newly defined in the present invention will be described.
First, the ECU 20 measures the in-cylinder pressure at three points in total, that is, two points in the compression stroke and one point in the expansion stroke, from signals from the in-cylinder pressure sensor 17 and the crank angle sensor 15.
That is, as shown in FIG. 1, the ECU 20 has a function of in-cylinder pressure detecting means 21 that measures the in-cylinder pressure of a total of three points including two compression strokes and one expansion stroke. Specifically, the means 21 has a cylinder pressure P (120B) (first combustion chamber pressure) at 120 ° before top dead center during the compression stroke of the internal combustion engine after the intake and exhaust valves are closed, and the cylinder pressure P ( In-cylinder pressure P (60B) (second combustion chamber pressure) during the compression stroke of the internal combustion engine at a timing after 120B) but before the ignition timing (60 ° before top dead center) The in-cylinder pressure at three points, that is, the in-cylinder pressure P (60A) (the third combustion chamber pressure) at 60 ° after the top dead center during the expansion stroke of the internal combustion engine when almost completed, is detected. The measurement points of the in-cylinder pressures P (120B), P (60B), and P (60A) at a total of three points including the above-described two compression strokes and one expansion stroke are shown in FIG. 1 or FIG. Become.
[0028]
Further, the ECU 20 calculates a combustion index Cio defined by the following equation (1) from the three in-cylinder pressures P (120B), P (60B), and P (60A) detected by the in-cylinder pressure detecting means 21. It has the function of the combustion index calculation means 22.
Cio =
(P (60A) -P (60B)) / (P (60B) -P (120B)) (1)
That is, the combustion index Cio is defined by the ratio of the difference between P (60A) and P (60B) and the difference between P (60B) and P (120B).
[0029]
Here, since the denominator (P (60B) -P (120B)) of the combustion index Cio has information on the compression pressure fluctuation, it has information on the amount of air into the combustion chamber 1 (including the EGR amount). Since the numerator (P (60A) -P (60B)) of the combustion index Cio has the expansion pressure fluctuation information, it has the engine output information. Therefore, the combustion index Cio is per unit air quantity. It will have the information of the engine output of.
[0030]
Further, the ECU 20 has a function of a comparison means 23 for obtaining a deviation ΔCi between the combustion index Cio obtained by the combustion index calculation means 22 and the reference combustion index (set value: threshold value) Cios.
Further, the ECU 20 has a function of a conversion means 24 for giving a dead zone and a weight as shown by a characteristic F in FIG. 1 to the deviation ΔCi obtained by the comparison means 23, and further, an output of the conversion means 24. It has a function of accumulating means 25 for accumulating F (ΔCi), and further has a function of a limiter means 26 for performing a limiter process on the output of the accumulating means 25. Based on the output of this limiter means 26, A feedback correction coefficient Kfb is determined. That is, during the air-fuel ratio feedback operation, while the output of the accumulating unit 25 does not exceed the upper limit value or the lower limit value, the output of the accumulating unit 25 exceeds the upper limit value or the lower limit value according to the accumulated output from the accumulating unit 25. Then, the feedback correction coefficient Kfb is updated so that the air-fuel ratio is adjusted according to the upper limit value or the lower limit value.
[0031]
Note that the feedback correction coefficient Kfb is not updated when it is not in the air-fuel ratio feedback operation region (steady operation region), so the ECU 20 does not update the feedback correction coefficient Kfb when it is not in the air-fuel ratio feedback operation region (steady operation region). Means for stopping (refer to air-fuel ratio feedback determination logic, switch means 27) is also provided.
[0032]
By the way, in order to confirm that the combustion index Cio has information on the engine output per unit air amount, the inventor operates the engine output (or engine misfire state) and the above combustion when the engine is operated near the lean combustion limit. I examined the relationship with the index Cio.
FIG. 8A shows the crank angle / combustion fluctuation characteristics when there is a margin for combustion, FIG. 9A shows the combustion index / engine output characteristics when there is a margin for combustion, and FIG. 8B shows the lean combustion. Crank angle / combustion fluctuation characteristics in the case of the limit, FIG. 9 (b) is a combustion index / engine output characteristic in the case of the lean combustion limit, and FIG. 8 (c) is a crank angle / combustion in the case of exceeding the lean combustion limit. The fluctuation characteristics, FIG. 9C, are the combustion index / engine output characteristics when the lean combustion limit is exceeded, and the following can be understood from these characteristic charts. 8A to 8C show the maximum value and minimum value characteristics of parameter fluctuation, that is, the envelope characteristics of all parameter fluctuations, and the area surrounded by the envelope characteristics. The smaller one indicates a situation where combustion is stable.
[0033]
First, when there is a margin in combustion, a combustion index Cio having a value larger than a certain value Cios (this value Cios corresponds to the above "threshold value") is concentrated at a substantially constant engine output. . When the lean combustion limit is reached, the combustion index Cio begins to disperse slightly, and when the lean combustion limit is exceeded, the combustion index Cio disperses to a portion where the engine output is low, and the combustion index Cio of the portion where the engine output is low It can be seen that it is below the threshold value Cios.
[0034]
From this, it can be seen that the combustion index Cio has a strong correlation with the engine output, and when the combustion index Cio falls below the threshold value Cios, it can be evaluated that the engine output has decreased and has exceeded the lean combustion limit. I understand that
FIG. 10 is a graph showing the relationship between the engine speed, the engine output, and the combustion index when the engine is operated under various operating conditions. From this graph, the combustion index indicates the engine load. It can be seen that it shows a substantially constant value regardless of the state, and it can be seen that when the fuel is cut during deceleration and the engine output decreases, the combustion index also decreases in conjunction with this.
[0035]
That is, it has been proved that the combustion index Cio and the engine output have a very strong correlation.
Therefore, in the vicinity of the lean combustion limit, a cycle with a small combustion index Cio begins to appear, and when the lean limit is approached, the output of the accumulating means 25 (integral information of the deviation) increases. When the feedback correction coefficient Kfb is updated so as to be rich, the misfire rate decreases, the combustion index Cio increases again, and the magnitude of the deviation integral information decreases.
[0036]
In this way, the ECU 20 controls the air-fuel ratio adjustment element as the combustion fluctuation adjustment element of the engine in the direction in which the magnitude of the accumulation information decreases based on the accumulation information of the deviation ΔCi obtained by the comparison means 23. It also has the function of a control means. In order to perform the control as described above, the combustion state of the engine is also evaluated based on the combustion index Cio. Therefore, the ECU 20 evaluates the combustion state of the engine based on the combustion index Cio. It also has the function of an evaluation means.
[0037]
Next, fuel injection control centering on the calculation of the feedback correction coefficient Kfb will be described with reference to the flowcharts of FIGS.
First, in step A1 of FIG. 3, the three in-cylinder pressures P (120B), P (60B), and P (60A) read as shown in FIGS. 4 to 6 are loaded. That is, the in-cylinder pressure P (120B) is read every 120 ° crank interruption before top dead center (step B1 in FIG. 4), and the in-cylinder pressure P (60B) is obtained every 60 ° crank interruption before top dead center. The in-cylinder pressure P (60A) is read every 60 ° crank interruption after top dead center (step D1 in FIG. 6).
[0038]
Thereafter, in step A2 of FIG. 3, the combustion index Cio is calculated based on the above equation (1), the deviation ΔCi is obtained in step A3, and if the air-fuel ratio feedback allowable operation state is established, the YES route of step A4 is followed. In step A5, the feedback correction coefficient Kfb is obtained based on the accumulated information of the deviation ΔCi, and thereafter the basic drive time T_BAnd other correction factors to calculate the fuel injection time T_inj(Step A7), this fuel injection time T_injThus, the injector 6 is driven (step A8).
[0039]
In this case, when the combustion index Cio falls below the predetermined threshold value Cios, the difference is integrated, and the feedback correction coefficient Kfb is increased according to the integrated value to enrich the air-fuel ratio. The engine can be operated in a state close to the limit. This greatly contributes to improvement of fuel consumption and reduction of NOx.
[0040]
Moreover, the advantage by utilizing said combustion parameter | index Cio is as follows.
(1) Since the in-cylinder pressure measurement points are as few as three, the amount of calculation for obtaining the combustion index Cio is small.
(2) Since the pressure difference is used for both the denominator and the numerator of the equation (Equation (1)) used when obtaining the combustion index Cio, the calculation for zero point calibration of the in-cylinder pressure becomes unnecessary.
[0041]
(3) Since the ratio of denominator and numerator is used to obtain the combustion index Cio, gain management of the in-cylinder pressure becomes unnecessary.
(4) Since the combustion index Cio has engine output information per unit air amount, the combustion index Cio can be set to a substantially constant value regardless of the engine load.
When the air-fuel ratio feedback allowable operation state is not established, the NO route of step A4 is taken, the feedback correction coefficient Kfb is set to “1” in step A6, and thereafter the basic drive time T_BAnd other correction factors to calculate the fuel injection time T_inj(Step A7), this fuel injection time T_injThen, the injector 6 is driven (step A8).
[0042]
Fuel injection time T_injSince this calculation is performed for each cylinder, the above fuel injection control is performed for each cylinder.
Thus, in this embodiment, focusing on the fact that a combustion index Cio defined using a small amount of detected in-cylinder pressure information is created, and the combustion state of the engine can be easily evaluated using this combustion index Cio, By using the combustion state evaluation method described above, it is possible to control the air-fuel ratio adjustment element as the engine combustion fluctuation adjustment element and control the combustion state of the engine, so that it is possible to easily realize lean combustion limit control. This contributes greatly to improving fuel efficiency and reducing NOx.
[0043]
It is theoretically possible to perform rich combustion limit control by evaluating the rich combustion limit using the combustion index Cio.
Further, the engine may be controlled in a direction in which the magnitude of the deviation ΔCi decreases by using the deviation ΔCi itself instead of the accumulated information of the deviation ΔCi between the combustion index Cio and the set value Cios.
[0044]
Further, as cylinder pressure measurement points, the first cylinder pressure and the first cylinder pressure at two different points in the compression stroke of the engine, in addition to 120 ° before top dead center, 60 ° before top dead center, 60 ° after top dead center, Three points of the two cylinder pressures and the third cylinder pressure in the expansion stroke of the internal combustion engine may be measured, and the combustion index is calculated based on the third cylinder pressure and the first and second cylinder pressures. You may define with ratio with the difference with one in-cylinder pressure, and the difference of said 1st, 2nd in-cylinder pressure. Even if the combustion index defined in this way is used, the combustion state of the engine can be evaluated and the combustion state of the engine can be controlled in the same manner as described above.
[0045]
Further, based on the comparison result between the combustion index and the threshold value, the EGR amount may be controlled instead of or in addition to the air-fuel ratio.
[0046]
【The invention's effect】
As described above in detail, according to the present invention, the combustion chamber pressure at a total of three points, that is, two points in the compression stroke of the internal combustion engine and one point in the expansion stroke of the internal combustion engine is detected, and combustion is performed from these combustion chamber pressures. Since the index is calculated and the combustion state of the internal combustion engine is evaluated based on this combustion index, the calculation amount for obtaining the combustion index is small, and the calculation for calibration of the zero point of the in-cylinder pressure is performed. And the gain management of the in-cylinder pressure can be made unnecessary, and this has the advantage that the combustion state of the engine can be easily evaluated.
[0047]
In addition, according to the present invention, the combustion state of the engine can be controlled by controlling the combustion fluctuation adjustment factor of the engine by using the above-described combustion state evaluation method, so that, for example, the lean combustion limit control is easily realized. This has the advantage of greatly contributing to improved fuel consumption and reduced NOx.
[Brief description of the drawings]
FIG. 1 is a control block diagram showing an embodiment of the present invention.
FIG. 2 is a schematic configuration diagram of an engine system equipped with the present apparatus.
FIG. 3 is a flowchart illustrating a control procedure according to an embodiment of the present invention.
FIG. 4 is a flowchart illustrating a control procedure according to an embodiment of the present invention.
FIG. 5 is a flowchart illustrating a control procedure according to an embodiment of the present invention.
FIG. 6 is a flowchart illustrating a control procedure according to an embodiment of the present invention.
FIG. 7 is a diagram for explaining pressure measurement points used for calculation of a combustion index.
FIG. 8 is a diagram for explaining a relationship between combustion fluctuations near a lean limit and a crank angle.
FIG. 9 is a diagram for explaining a correlation between a combustion index near the lean limit and an engine output.
FIG. 10 is a diagram for explaining a relationship among a combustion index, an engine output, and an engine speed.
FIG. 11 is a diagram for explaining the relationship between the air-fuel ratio, combustion fluctuation, and NOx amount.
[Explanation of symbols]
1 Combustion chamber
2 Air intake passage
2a Surge tank
3 Exhaust passage
4 Intake valve
5 Exhaust valve
6 Injector
7 EGR passage
8 EGR valve
9 Air flow sensor
10 Intake air temperature sensor
11 Atmospheric pressure sensor
12 Throttle sensor
13 O₂Sensor
14 Water temperature sensor
15 Crank angle sensor
16 TDC sensor
17 In-cylinder pressure sensor
18 Spark plug
20 ECU
21 In-cylinder pressure detection means
22 Combustion index calculation means
23 Comparison means
24 Conversion means
25 Cumulative means
26 Limiter means
27 Switch means

Claims (9)

The three combustion chambers of the first combustion chamber pressure and the second combustion chamber pressure at two different points in the compression stroke of the internal combustion engine that can be operated near the lean combustion limit and the third combustion chamber pressure in the expansion stroke of the internal combustion engine After detecting pressure,
A combustion index defined by a ratio between the difference between the pressure in the third combustion chamber and the pressure in one of the first and second combustion chambers and the difference between the pressures in the first and second combustion chambers is calculated. ,
When the combustion index falls below a predetermined value, and evaluates with the internal combustion engine exceeds a lean combustion limit, the combustion state evaluation method for an internal combustion engine. In time there is before the ignition timing at timing later than the first combustion chamber pressure and the first combustion chamber pressure during the compression stroke of the intake and exhaust valves after engaging of the internal combustion engine which can be operated in the lean combustion limit near In-cylinder pressure detecting means for detecting three pressures in the combustion chamber, that is, a pressure in the second combustion chamber during the compression stroke of the internal combustion engine and a pressure in the third combustion chamber during the expansion stroke of the internal combustion engine at the time when combustion is substantially completed;
A combustion index defined by a ratio between the difference between the third combustion chamber pressure and the second combustion chamber pressure detected by the in-cylinder pressure detecting means and the difference between the first and second combustion chamber pressures is calculated. Combustion index calculation means;
When combustion index calculated by the combustion index computing means falls below a predetermined value, characterized in that the internal combustion engine is constructed to include an evaluation means for evaluating that exceeds the lean combustion limit, the internal combustion engine Combustion state evaluation device. At least three points of the first combustion chamber pressure and the second combustion chamber pressure at two different points in the compression stroke of the internal combustion engine that can be operated near the lean combustion limit, and the third combustion chamber pressure in the expansion stroke of the internal combustion engine. In-cylinder pressure detecting means for detecting the pressure in the combustion chamber;
A ratio between the difference between the third combustion chamber pressure detected by the in-cylinder pressure detecting means and the pressure in one combustion chamber between the first and second combustion chamber pressures and the difference between the first and second combustion chamber pressures. Combustion index calculation means for calculating a combustion index defined by
A comparison means for comparing the combustion index calculated by the combustion index calculation means with a set value;
Control means for controlling a combustion fluctuation adjusting element of the internal combustion engine in a direction in which the magnitude of the deviation decreases based on a deviation between the combustion index obtained by the comparison means and the set value. A combustion state control device for an internal combustion engine, characterized by comprising: At least three points of the first combustion chamber pressure and the second combustion chamber pressure at two different points in the compression stroke of the internal combustion engine that can be operated near the lean combustion limit, and the third combustion chamber pressure in the expansion stroke of the internal combustion engine. In-cylinder pressure detecting means for detecting the pressure in the combustion chamber;
A ratio between the difference between the third combustion chamber pressure detected by the in-cylinder pressure detecting means and the pressure in one combustion chamber between the first and second combustion chamber pressures and the difference between the first and second combustion chamber pressures. Combustion index calculation means for calculating a combustion index defined by
A comparison means for comparing the combustion index calculated by the combustion index calculation means with a set value;
Control means for controlling a combustion fluctuation adjusting element of the internal combustion engine in a direction in which the magnitude of the cumulative information decreases based on cumulative information of deviation between the combustion index and the set value obtained by the comparison means; /> characterized in that it is configured to include a internal combustion engine combustion state control device. Control means, characterized <br/> has a function of converting means for imparting the dead zone, the weights to the deviation between the obtained combustion indicator and setting value in said comparing means, according to claim 3 Or the combustion state control apparatus of the internal combustion engine of 4. The combustion state control device for an internal combustion engine according to any one of claims 3 to 5, wherein the combustion fluctuation adjustment element is an air-fuel ratio adjustment element of the internal combustion engine. The three combustion chambers of the first combustion chamber pressure and the second combustion chamber pressure at two different points in the compression stroke of the internal combustion engine that can be operated near the lean combustion limit, and the third combustion chamber pressure in the expansion stroke of the internal combustion engine. After detecting pressure,
A combustion index defined by a ratio between the difference between the pressure in the third combustion chamber and the pressure in one of the first and second combustion chambers and the pressure in the first and second combustion chambers is calculated. ,
Compare the combustion index with a set value,
Based on the deviation between the combustion index and the set value, the combustion fluctuation adjusting element of the internal combustion engine is controlled in a direction in which the magnitude of the deviation decreases.
A combustion state control method for an internal combustion engine. The three combustion chambers of the first combustion chamber pressure and the second combustion chamber pressure at two different points in the compression stroke of the internal combustion engine that can be operated near the lean combustion limit, and the third combustion chamber pressure in the expansion stroke of the internal combustion engine. After detecting pressure,
A combustion index defined by a ratio between the difference between the pressure in the third combustion chamber and the pressure in one of the first and second combustion chambers and the pressure in the first and second combustion chambers is calculated. ,
Compare the combustion index with a set value,
Based on the accumulated information of deviation between the combustion index and the set value, the combustion fluctuation adjustment element of the internal combustion engine is controlled in a direction in which the magnitude of the accumulated information decreases.
A combustion state control method for an internal combustion engine. A combustion state evaluation device for an internal combustion engine according to claim 2,
Control means for controlling a combustion fluctuation adjusting element of the internal combustion engine based on an evaluation result of the evaluation means in the combustion state evaluation device;
A combustion state control device for an internal combustion engine, characterized by comprising:

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