JPH06249049A - Method and device for evaluating combustion state of internal combustion engine and combustion state control device - Google Patents

Abstract

PURPOSE:To improve the fuel consumption and reduce NOx by evaluating the combustion state of the engine by the combustion index to be defined by using a small quantity of information on the pressure in detected cylinders, and thereby realizing the lean combustion critical control. CONSTITUTION:An intra-cylinder pressure detecting means 21 measures the intra-cylinder pressure at three points in total including two in compression stroke and one in expansion stroke by the signals from an intra-cylinder pressure sensor 17, and a crank angle sensor 15. A combustion index computing means 22 computes the combustion index Cio to be defined by the specified expression by using three detected intra-cylinder pressures. As for this Cio, when the combustion has a margin, the combustion index Cio which is larger than the value Cios is concentrated at the approximtely constant engine output. In the lean combustion critical condition, the combustion index Cio starts to be slightly dispersed, and when the lean combustion critical condition is passed, the combustion index is dispersed to the range where the engine output is low. This constitution allows the judgement of the combustion condition.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an internal combustion engine (engine).
The present invention relates to a method for evaluating a combustion state including the lean combustion limit, an apparatus for implementing the method, and a combustion state control apparatus for an internal combustion engine using the combustion state evaluation method.

[0002]

2. Description of the Related Art Generally, when the air-fuel ratio of an air-fuel mixture supplied to an engine is made lean (lean) and burned lean,
As shown in FIG. 11, it is known that the NOx generation amount in the lean combustion region is significantly reduced by the lean conversion. Therefore, from the viewpoint of NOx reduction,
It is effective to operate the engine with the set air-fuel ratio further to the lean limit side.

Therefore, various lean burn engines for leaner 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. Further, in such a lean burn engine, generally, a linear air-fuel ratio sensor (LAFS) is used to perform air-fuel ratio feedback control.

[0004]

However, in the lean burn engine described above, the target air-fuel ratio is set to a rich side of about 1 to 2 in terms of the air-fuel ratio from the lean limit in consideration of variations in the engine and the sensor or environmental factors. Therefore, there is room for further improvement from the viewpoint of reducing fuel consumption and NOx.

By the way, as a method of knowing the lean limit, the output torque fluctuation of the engine and the misfire state of the cylinder may be detected. For example, in the former case, the in-cylinder pressure corresponding to five different crank angles is used. There is one that detects (combustion chamber pressure) and obtains the output torque fluctuation of the engine from these cylinder pressures (see Japanese Patent Application Laid-Open No. 2-67446), and as an example of the latter, there are two points in the compression stroke. Obtain the offset component of the pressure sensor from the in-cylinder pressure, obtain the explosion stroke pressure information from this offset component and the in-cylinder pressure during the explosion stroke, and if this explosion stroke pressure information is below a predetermined value, the cylinder is in a misfire state. What is judged to have become
-104033).

However, the former example (Japanese Patent Laid-Open No. 2-67446)
In the Japanese Patent Laid-Open Publication No. 2003-242242, many (5 points) in-cylinder pressures have to be detected, and there is a problem in that the detected in-cylinder pressures need to be calculated for zero point calibration. Further, in the latter example (see Japanese Patent Laid-Open No. 104033/1998), only a small amount of in-cylinder pressure needs to be detected, but a calculation for zero point calibration of the detected in-cylinder pressure and a gain of the detected in-cylinder pressure are performed. There is a problem that management is required.

The present invention was devised in view of the above problems. A combustion index defined by using a small amount of detected in-cylinder pressure information is created, and the combustion state of the internal combustion engine is calculated using this combustion index. It is an object of the present invention to provide a combustion state evaluation method and apparatus for an internal combustion engine, which enables easy evaluation of the above. Further, the present invention, by utilizing the above combustion state evaluation method, by controlling the combustion fluctuation adjusting element of the internal combustion engine,
An object of the present invention is to provide a combustion state control device for an internal combustion engine, which can control the combustion state of the internal combustion engine.

[0008]

Therefore, the combustion state evaluation method for an internal combustion engine of the present invention comprises the following steps. (1) A step of detecting three combustion chamber pressures of 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) 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.
Calculating a combustion index defined by the ratio to the pressure difference in the combustion chamber. (3) A step of evaluating the combustion state of the internal combustion engine based on the combustion index.

Further, in the combustion state evaluating apparatus for an internal combustion engine of the present invention, the first combustion chamber pressure during the compression stroke of the internal combustion engine after the intake and exhaust valves are closed, and ignition is performed at a timing later than the first combustion chamber pressure. A cylinder for detecting the pressure in the combustion chamber at three points, that is, the pressure in the second combustion chamber during the compression stroke of the internal combustion engine before the timing and the pressure in the third combustion chamber during the expansion stroke of the internal combustion engine when the combustion is almost completed. It is defined by the internal pressure detection means and the ratio of the difference between the pressure of the third combustion chamber and the pressure of the second combustion chamber detected by the pressure detection means of the cylinder and the difference between the pressures of the first and second combustion chambers. It is characterized by comprising a combustion index calculation means for calculating a combustion index and an evaluation means for evaluating the combustion state of the internal combustion engine based on the combustion index calculated by the combustion index calculation means.

Furthermore, the combustion state control apparatus for an internal combustion engine according to the present invention includes at least the first combustion chamber pressure and the second combustion chamber pressure at two different points in the compression stroke of the internal combustion engine, and the first combustion chamber pressure in the internal combustion engine expansion stroke. 3 with 3 combustion chamber pressure
In-cylinder pressure detecting means for detecting the pressure in the combustion chamber at a certain point, the difference between the pressure in the third combustion chamber and the pressure in one of the first and second combustion chambers detected by the in-cylinder pressure detecting means, and Combustion index calculation means for calculating a combustion index defined by the ratio of the pressure difference between the first and second combustion chambers, and comparison means for comparing the combustion index calculated by the combustion index calculation means with a set value. A control means for controlling the combustion fluctuation adjusting element of the internal combustion engine based on the comparison result of the comparison means is provided.

The internal combustion engine is constructed as an internal combustion engine capable of operating near the lean combustion limit, and the control means is based on the deviation between the combustion index and the set value obtained by the comparison means. Is configured to control the combustion fluctuation adjusting element of the internal combustion engine in the direction of decreasing the magnitude of the above, or based on the accumulated information of the deviation between the combustion index and the set value obtained by the comparison means, It may be configured to control the combustion fluctuation adjusting element of the internal combustion engine in the direction of decreasing the amount of information.

As the combustion fluctuation adjusting element, for example, an air-fuel ratio adjusting element of an internal combustion engine can be considered.

[0013]

In the above-described combustion state evaluation method for an internal combustion engine of the present invention, first, the first combustion chamber pressure and the second combustion chamber pressure at two different points in the compression stroke of the internal combustion engine, and the first combustion chamber pressure in the internal combustion engine expansion stroke. The three combustion chamber pressures including the third combustion chamber pressure are detected, and then the difference between the third combustion chamber pressure and one of the first and second combustion chamber pressures, and the first and second combustion chamber pressures. A combustion index defined by the ratio to the pressure difference in the combustion chamber is calculated, and the combustion state of the internal combustion engine is evaluated based on this combustion index.

Further, in the combustion state evaluation apparatus for an internal combustion engine according to the present invention, the in-cylinder pressure detecting means determines whether the first internal combustion engine compression stroke is being performed.
The pressure in the combustion chamber and the pressure in the second combustion chamber are detected, and the pressure in the third combustion chamber during the expansion stroke of the internal combustion engine is detected. Then, a combustion index defined by the ratio between the difference between the pressure in the third combustion chamber and the pressure in the second combustion chamber detected by the in-cylinder pressure detection means and the ratio between the pressure in the first and second combustion chambers is burned. The combustion state of the internal combustion engine is evaluated based on the combustion index calculated by the combustion index calculation means by the index calculation means.

Further, in the combustion state control apparatus for an internal combustion engine according to the present invention, the in-cylinder pressure detecting means detects the first combustion chamber pressure and the second combustion chamber pressure at two different points in the compression stroke of the internal combustion engine, and the internal combustion engine. The pressure in the combustion chamber at three points, which is the pressure in the third combustion chamber in the expansion stroke, is detected, and then the combustion index calculation unit detects the pressure in the third combustion chamber and the first and second combustion chambers. A combustion index defined by the ratio of the difference between the internal pressure of one of the combustion chambers and the pressure of the first and second combustion chambers is calculated, and further calculated by the comparison means by the combustion index calculation means. After comparing the combustion index and the set value, the control means controls the combustion fluctuation adjusting element of the internal combustion engine based on the comparison result of the comparison means.

Incidentally, the internal combustion engine is constructed as an internal combustion engine which can be operated in the vicinity of the lean combustion limit, and in the control means, based on the deviation between the combustion index and the set value obtained by the comparison means,
Cumulative information on the deviation between the combustion index and the set value obtained by the comparison means for controlling the combustion fluctuation adjusting element of the internal combustion engine (for example, the air-fuel ratio adjusting element of the internal combustion engine) in the direction of decreasing the magnitude of the deviation. Based on the above, the combustion fluctuation adjusting element of the internal combustion engine (for example, the air-fuel ratio adjusting element of the internal combustion engine) may be controlled in the direction of decreasing the amount of cumulative information.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIGS. 1 to 10 show an engine combustion state control apparatus using an engine combustion state evaluation method as one embodiment of the present invention. FIG. 1 is a control block diagram thereof, FIG. 2 is a schematic configuration diagram of an engine system equipped with the present device, FIGS. 3 to 6 are flowcharts for explaining the control procedure, and FIG. 7 is used for calculation of a combustion index. FIG. 8 is a diagram illustrating a pressure measurement point, FIG. 8 is a diagram illustrating a relationship between a combustion fluctuation and a crank angle near the lean limit, and FIG. 9 is a diagram illustrating a correlation between a combustion index and an engine output near the lean limit. FIG. 10 is a diagram for explaining the relationship between the combustion index, the engine output, and the engine speed.

An engine system having this device is as shown in FIG. 2. In FIG. 2, an engine (internal combustion engine) EG has an intake passage 2 and an exhaust passage 3 which communicate with a combustion chamber 1. The intake passage 2 and the combustion chamber 1 are controlled by the intake valve 4, and the exhaust passage 3 and the combustion chamber 1 are controlled by the exhaust valve 5.

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 this order from the upstream side, and the exhaust passage 3 is provided with an upstream side thereof. A catalytic converter for purifying exhaust gas and a muffler (silencer) (neither shown) are provided in this order from the side. The intake passage 2 is provided with a surge tank 2a, and further the injector 6 is provided.
Are provided in the intake port portion corresponding to each cylinder.

An exhaust gas recirculation passage (EGR passage) 7 is provided between the intake passage 2 and the exhaust passage 3, and an electromagnetic EGR valve 8 is provided in the EGR passage 7. Has been done. In addition, 18 is a spark plug. further,
Various sensors are provided to control the engine EG. First, an in-cylinder pressure sensor 17 for detecting the 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 is further provided.
(This crank angle sensor 15 also serves as a rotation speed sensor for detecting the engine rotation speed).

On the intake passage 2 side, an air flow sensor (intake air amount sensor) 9 for detecting the intake air amount from the Karman vortex information, an intake air temperature sensor 10 for detecting the intake air temperature, and a large portion are provided in the air cleaner disposition portion. An atmospheric pressure sensor 11 that detects the atmospheric pressure is provided, and a potentiometer-type throttle sensor 12 that detects the opening of the throttle valve is provided at the portion where the throttle valve is provided.

Further, on the exhaust passage 3 side, at an upstream side portion of the catalytic converter, an air-fuel ratio sensor 13 (hereinafter, simply referred to as "O ₂ sensor 1" for detecting oxygen concentration (O ₂ concentration) in exhaust gas).
3 ”). As other sensors, a water temperature sensor 14 for detecting the engine cooling water temperature and a T for detecting the top dead center of the first cylinder (reference cylinder)
A DC sensor (cylinder discrimination sensor) 16 is also provided.

The detection signals from these sensors are input to the electronic control unit (ECU) 20, which is a CPU, ROM, R.
AM, which has an appropriate input / output interface, and when a detection signal from each of the above-described sensors is input to the CPU of the ECU 20, a required calculation is performed by the CPU, and fuel injection amount control based on the calculation result. The signal (fuel amount control signal), the ignition timing control signal, and the EGR control signal are output to the injector 6, the ignition plug 18, and the EGR valve 8, respectively.

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 injector 6 receives this fuel injection amount control signal. Is the fuel injection time T _inj (= T _B × Kaf × K × (1 + Kfb) + Tacc)
During that time, it is designed to drive. Here, T _B is the basic drive time, and this basic drive time T _B is determined according to the intake air amount information per revolution of the engine obtained from the air flow sensor 9 and the crank angle sensor 15.

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 air flow sensor 9 or the like, and is a value smaller than "1" during lean operation. Is set. Kfb is a feedback correction coefficient, and this feedback correction coefficient Kfb
Is set based on the combustion index Cio described later.

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. 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 cooling water temperature obtained by the water temperature sensor 14, and the like can be considered.

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 in-cylinder pressures at a total of 3 points, that is, 2 compression stroke points and 1 expansion stroke point, 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 an in-cylinder pressure detecting means 21 for measuring in-cylinder pressures at a total of three points, that is, two compression strokes and one expansion stroke. In the means 21, specifically, the in-cylinder pressure P (12 at 120 ° before the top dead center during the compression stroke of the internal combustion engine after the intake and exhaust valves are closed.
0B) (the pressure in the first combustion chamber) and the in-cylinder pressure P (1
20B) but before the ignition timing (60 ° before top dead center) before the ignition timing, the cylinder pressure P (60B) (second combustion chamber pressure) during the compression stroke of the internal combustion engine and the combustion 60 after top dead center in the expansion stroke of the internal combustion engine at the time of almost completion
The in-cylinder pressure P (60A) (third combustion chamber pressure) at three degrees and the in-cylinder pressure at three points are detected. In addition, in-cylinder pressure P (12) of three points in total including the above two points of the compression stroke and one point of the expansion stroke.
0B), P (60B), and P (60A) are shown in FIG. 1 or FIG.

Further, the ECU 20 has a cylinder pressure detecting means 21.
Three in-cylinder pressures P (120B), P (60
B) and P (60A) have the function of the combustion index calculation means 22 for calculating the combustion index Cio defined by the following equation (1). Cio = (P (60A) -P (60B)) / (P (60B) -P (120B)) ... (1) That is, the combustion index Cio is P (60A) and P (60).
B) and the difference between P (60B) and P (120B).

Here, the denominator (P (6
0B) -P (120B)) has the information on the amount of air (including the EGR amount) into the combustion chamber 1 because it has the compression pressure fluctuation information, and the numerator of the combustion index Cio (P (6
0A) -P (60B)) has the information of the engine output because it has the expansion pressure fluctuation information, and therefore the combustion index Cio has the information of the engine output per unit air amount.

Further, the ECU 20 uses the combustion index calculation means 2
The combustion index Cio obtained in 2 and the reference combustion index (setting value:
Comparison means 23 for obtaining a deviation ΔCi from the threshold value) Cios
It has the function of. Further, the ECU 20 has a function of a converting 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 comparing means 23, and further, an output of the converting means 24. It has a function of the 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 the limiter means 26, The feedback correction coefficient Kfb is determined. That is, during the air-fuel ratio feedback operation, while the output of the accumulating means 25 does not exceed the upper limit value or the lower limit value, the output of the accumulating means 25 exceeds the upper limit value or the lower limit value according to the accumulated output from the accumulating means 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.

Note that the feedback correction coefficient Kfb is not updated when it is not in the air-fuel ratio feedback operation area (steady operation area), so the ECU 20 does not update the feedback correction coefficient Kfb when it is not in the air-fuel ratio feedback operation area (steady operation area). It also has a means for stopping the updating of the above (see the air-fuel ratio feedback determination logic, switch means 27).

By the way, the present inventor confirms that the combustion index Cio has information on the engine output per unit amount of air, so that the engine output (or engine misfire state) when the engine is operated near the lean combustion limit. The relationship between the above-mentioned combustion index and Cio was investigated. FIG. 8A shows a crank angle / combustion fluctuation characteristic when there is a margin in combustion,
9 (a) is a combustion index / engine output characteristic when there is a margin of combustion, FIG. 8 (b) is a crank angle / combustion fluctuation characteristic in the case of lean combustion limit, and FIG. 9 (b) is a lean combustion limit. 8 (c) is a combustion index / engine output characteristic in the case of, and FIG. 8 (c) is a crank angle / combustion fluctuation characteristic in the case of exceeding the lean combustion limit, and FIG. 9 (c) is a combustion index in the case of exceeding the lean combustion limit. Regarding the engine output characteristics, the following can be seen from these characteristic diagrams. Note that FIG.
In (c), the maximum and minimum value characteristics of the parameter fluctuation are shown, that is, the envelope characteristics of all the parameter fluctuations are shown, and the smaller the area surrounded by the envelope characteristics, the more stable the combustion. It shows the situation.

First, when there is a margin in combustion, a certain value Cios (this value Cio
The combustion index Cio having a value larger than s (corresponding to the above "threshold value") is concentrated. Then, when the lean combustion limit is reached, the combustion index Cio begins to slightly disperse, and when the lean combustion limit is exceeded, the combustion index Cio disperses even to the portion where the engine output is low, and the combustion index Cio for the portion where the engine output is low is calculated. It can be seen that it is below the threshold value Cios.

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 becomes lower than the threshold value Cios, the engine output lowers and exceeds the lean combustion limit. You can see that you can evaluate. Further, 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 is the engine load. It can be seen that it shows a nearly constant value regardless of the state, and if the engine output drops when fuel is cut during deceleration, the combustion index also drops in conjunction with this.

That is, it was 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 in which the combustion index Cio is small begins to appear, and when the lean limit is approached, the output of the accumulating means 25 (integral information of the deviation) increases, but the air-fuel ratio is changed accordingly. 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 integration information decreases.

In this way, the ECU 20 adjusts the air-fuel ratio as a combustion fluctuation adjusting element of the engine in the direction of decreasing the magnitude of the accumulated information based on the accumulated information of the deviation ΔCi obtained by the comparison means 23. It will also have the function of control means for controlling the elements. Further, in order to perform the above control, the combustion state of the engine is also evaluated based on the above combustion index Cio.
It also has a function of an evaluation means for evaluating the combustion state of the engine based on the combustion index Cio.

Next, the above feedback correction coefficient Kfb
Regarding the fuel injection control centered on the calculation of
This will be described with reference to the flowchart of FIG. First, in step A1 of FIG. 3, the three in-cylinder pressures P (120B), P (60B), P read as shown in FIGS.
Load (60A). That is, the cylinder pressure P (120
B) is read at every 120 ° crank interrupt before top dead center (step B1 in FIG. 4), and the cylinder pressure P (60B) is read at every 60 ° crank interrupt before top dead center (step in FIG. 5). C1), cylinder pressure P (60A) is 60 after top dead center
It is read at every crank interruption of ° (step D1 in FIG. 6).

After that, in step A2 of FIG. 3, the combustion index Cio is calculated based on the equation (1), and step A
In step 3, the deviation ΔCi is obtained, and if the air-fuel ratio feedback allowable operating state is reached, the YES route of step A4 is taken, and in step A5, the feedback correction coefficient Kfb is obtained based on the accumulated information of the deviation ΔCi, and thereafter the basic drive is performed. The time T _B and other correction factors are calculated to obtain the fuel injection time T _inj (step A7).
_The injector 6 is driven by _inj (step A)
8).

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.
Since the air-fuel ratio is made rich, the engine can be operated in a state close to the lean combustion limit. This greatly contributes to improvement of fuel consumption and reduction of NOx.

The advantages of using the above combustion index Cio are as follows. (1) Since the number of measuring points for the in-cylinder pressure is as small as three, the amount of calculation for obtaining the combustion index Cio can be small. (2) Formula used to calculate the combustion index Cio ((1)
Since the pressure difference is used for both the denominator and the numerator in (Equation), the calculation for zero-point calibration of the in-cylinder pressure becomes unnecessary.

(3) Since the ratio of the denominator and the numerator is used to obtain the combustion index Cio, gain control of the in-cylinder pressure becomes unnecessary. (4) Since the combustion index Cio has engine output information per unit amount of air, the combustion index Cio can be set to a substantially constant value regardless of the engine load. If the air-fuel ratio feedback allowable operation state is not set, the NO route of step A4 is taken and step A6 is executed.
Then, the feedback correction coefficient Kfb is set to "1", and thereafter, the basic drive time T _B and other correction coefficients are calculated to obtain the fuel injection time T _inj (step A7), and the injector is injected at this fuel injection time T _inj . 6 is driven (step A8).

Since the fuel injection time T _inj is calculated for each cylinder, the above fuel injection control is executed for each cylinder. As described above, in this embodiment, the combustion index Cio defined by using a small amount of detected in-cylinder pressure information is created,
Focusing on the fact that the combustion state of the engine can be easily evaluated using the combustion index Cio, the air-fuel ratio adjustment element as the combustion variation adjustment element of the engine is controlled by using the above-mentioned combustion state evaluation method. Since the combustion state of the engine can be controlled, lean combustion limit control can be easily realized, which greatly contributes to improvement of fuel consumption and reduction of NOx.

It is theoretically possible to evaluate the rich combustion limit using the combustion index Cio and perform the rich combustion limit control. Further, instead of the accumulated information of the deviation ΔCi between the combustion index Cio and the set value Cios, the deviation ΔCi
It is also possible to use i itself to control the engine in the direction in which the magnitude of this deviation ΔCi decreases.

Further, as the in-cylinder pressure measurement points, 120 ° before top dead center, 60 ° before top dead center, and 60 ° after top dead center, and in the first cylinder at two different points in the compression stroke of the engine. The pressure and the second in-cylinder pressure and the third in-cylinder pressure in the internal combustion engine expansion stroke may be measured at three points, and the combustion index may be the above-mentioned third in-cylinder pressure and the first and second cylinders. It may be defined by the ratio of the difference between the internal pressure of one of the cylinder pressures and the difference between the first and second cylinder pressures. By using the combustion index defined in this way, the combustion state of the engine can be evaluated and the combustion state of the engine can be controlled in the same manner as in the above case.

Further, based on the result of comparison between the combustion index and the threshold value, instead of the air-fuel ratio or in addition to the air-fuel ratio, the EGR
The amount may be controlled.

[0046]

As described in detail above, according to the present invention,
The combustion chamber pressures of three points in total, two points in the compression stroke of the internal combustion engine and one point in the internal combustion engine expansion stroke, are detected, a combustion index is calculated from these combustion chamber pressures, and internal combustion is performed based on this combustion index. Since the combustion state of the engine is evaluated, the amount of calculation for obtaining the combustion index is small, the calculation for zero-point calibration of the cylinder pressure is unnecessary, and the gain management of the cylinder pressure is also possible. It can be made unnecessary, which has the advantage that the combustion state of the engine can be evaluated easily.

Further, according to the present invention, the combustion state of the engine can be controlled by controlling the combustion fluctuation adjusting element of the engine by utilizing the above-mentioned combustion state evaluation method. The control can be realized, which has the advantage of contributing greatly to the improvement of fuel consumption and NOx reduction.

[Brief description of 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 this device.

FIG. 3 is a flowchart illustrating a control procedure of an embodiment of the present invention.

FIG. 4 is a flowchart illustrating a control procedure of an embodiment of the present invention.

FIG. 5 is a flowchart illustrating a control procedure of an embodiment of the present invention.

FIG. 6 is a flowchart illustrating a control procedure of an embodiment of the present invention.

FIG. 7 is a diagram illustrating pressure measurement points used to calculate a combustion index.

FIG. 8 is a diagram illustrating a relationship between combustion fluctuation and a crank angle in the vicinity of a lean limit.

FIG. 9 is a diagram illustrating a correlation between a combustion index and an engine output near the lean limit.

FIG. 10 is a diagram illustrating a relationship among a combustion index, an engine output, and an engine speed.

FIG. 11 is a diagram illustrating a relationship between an air-fuel ratio, combustion fluctuations, and NOx amount.

[Explanation of symbols]

1 Combustion Chamber 2 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 Temperature Sensor 11 Atmospheric Pressure Sensor 12 Throttle Sensor 13 O ₂ Sensor 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 Accumulation means 26 Limiter means 27 Switch means

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Kazuhide Tsuga 5-3-8, Shiba, Minato-ku, Tokyo Inside Mitsubishi Motors Corporation

Claims (6)

[Claims] 1. A combustion chamber pressure at three points of a first combustion chamber pressure and a second combustion chamber pressure at two different points in a compression stroke of an internal combustion engine and a third combustion chamber pressure at an internal combustion engine expansion stroke is detected. Then, a combustion index defined by the 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 in the pressure in the first and second combustion chambers. Is calculated, and the combustion state of the internal combustion engine is evaluated based on the combustion index. 2. A first combustion chamber pressure during a compression stroke of the internal combustion engine after the intake and exhaust valves are closed, and an internal combustion engine compression stroke at a timing after the first combustion chamber pressure but before the ignition timing. In-cylinder pressure detecting means for detecting three internal combustion chamber pressures, namely, the second combustion chamber pressure and the third combustion chamber pressure during the expansion stroke of the internal combustion engine at the time when the combustion is almost completed, and the in-cylinder pressure detecting means. Combustion index calculation means for calculating a combustion index defined by a ratio between the difference between the pressure in the third combustion chamber and the pressure in the second combustion chamber and the difference between the pressures in the first and second combustion chambers, Based on the combustion index calculated by the combustion index calculation means,
A combustion state evaluation device for an internal combustion engine, comprising: an evaluation means for evaluating the combustion state of the internal combustion engine. 3. A combustion chamber pressure at least at three points, namely, a first combustion chamber pressure and a second combustion chamber pressure at two different points in a compression stroke of the internal combustion engine, and a third combustion chamber pressure at an internal combustion engine expansion stroke. In-cylinder pressure detecting means, a difference between the pressure in the third combustion chamber and the pressure in one of the first and second combustion chambers detected by the in-cylinder pressure detecting means, and the first and the first in-cylinder pressures. 2 Combustion index calculation means for calculating a combustion index defined by the ratio of the pressure difference between the combustion chambers, comparison means for comparing the combustion index calculated by the combustion index calculation means with a set value, and the comparison means And a control means for controlling a combustion fluctuation adjusting element of the internal combustion engine based on the comparison result of 1. 4. The internal combustion engine is an internal combustion engine capable of operating in the vicinity of a lean combustion limit, and the control means uses the deviation based on the deviation between the combustion index obtained by the comparison means and the set value. 4. The combustion state control device for an internal combustion engine according to claim 3, wherein the combustion variation control element for the internal combustion engine is configured to be controlled in a direction in which the magnitude of the internal combustion engine decreases. 5. The combustion fluctuation of the internal combustion engine in a direction in which the magnitude of the cumulative information is decreased by the control means based on the cumulative information of the deviation between the combustion index and the set value obtained by the comparing means. 5. Combustion state control device for an internal combustion engine according to claim 4, characterized in that it is arranged to control the adjusting element. 6. The combustion state control device for an internal combustion engine according to claim 3, wherein the combustion fluctuation adjusting element is an air-fuel ratio adjusting element for the internal combustion engine.