JPH11193735A - Air-fuel ratio control system for internal combustion engine and method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to maintain the operating state of an engine stable in a condition where the air-fuel ratio becomes lean by detecting a pressure within a cylinder of an internal combustion engine, integrating the detected pressure within the cylinder to obtain the integrated value, and controlling the air-fuel ratio of a mixture supplied to the engine in accordance with the integrated value. SOLUTION: Cylinder internal pressure sensors 5 to 8 each having a piezoelectric element as a sensor element portion for detecting the pressure within the cylinder are disposed on the respective cylinder heads of cylinders 1 to 4 of an internal combustion engine. The voltage generated by the sensor element portion is integrated and amplified. The resultant value is sent to an ECU 21 which receives inputs of output signals of an intake pipe internal pressure sensor 39, a cooling water temperature sensor 40, a throttle opening sensor, and the like. Then CPU 31 obtains a mean effective pressure from data of the internal pressure of the cylinder at 1 cycle that have been detected by the cylinder internal pressure sensor 5. The obtained mean effective pressure is compared with a threshold value set in accordance with an engine speed. Depending on the comparison result, the correction factor of the air-fuel ratio is increased or decreased for correction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an air-fuel ratio control apparatus and method for controlling an air-fuel ratio of an air-fuel mixture supplied to an internal combustion engine.

[0002]

2. Description of the Related Art There is known an air-fuel ratio control device for lean-burning an air-fuel ratio of an air-fuel mixture supplied to an internal combustion engine by performing lean control based on the pressure in the cylinder, that is, the in-cylinder pressure. For example, Japanese Patent Laying-Open No. 62-150058 discloses that the air-fuel ratio is controlled lean according to the ratio between the maximum value and the minimum value of the in-cylinder pressure detected by the in-cylinder pressure sensor.

[0003]

However, in such a conventional air-fuel ratio control device, the ratio between the maximum value and the minimum value of the in-cylinder pressure detected by the in-cylinder pressure sensor is used, so that the combustion state of the engine is appropriately predicted. However, there is a problem that it is easy to cause a misfire in which the combustion becomes abnormal due to leaning, and it is difficult to maintain a stable operation state.

Accordingly, an object of the present invention is to provide an air-fuel ratio control apparatus and method capable of maintaining a stable engine operating state even when the air-fuel ratio of a supplied air-fuel mixture is made lean for lean combustion. is there.

[0005]

An air-fuel ratio control apparatus according to the present invention comprises an in-cylinder pressure detecting means for generating an in-cylinder pressure detection signal corresponding to a pressure in a cylinder of an internal combustion engine, and an integration by integrating the in-cylinder pressure detection signal. An integration means for obtaining a value, a comparison means for comparing the integration value with a threshold value, and an air-fuel ratio adjusting means for controlling an air-fuel ratio of an air-fuel mixture supplied to the engine according to the integration value. .

According to the air-fuel ratio control method of the present invention, the pressure in a cylinder of an internal combustion engine is detected, the detected pressure in the cylinder is integrated to obtain an integral value, and the mixture supplied to the engine is determined according to the integral value. It is characterized by controlling the air-fuel ratio. That is, according to the present invention, since the integrated value is obtained by integrating the detected pressure in the cylinder, the combustion state of the engine can be determined from the integrated value. Therefore, by controlling the air-fuel ratio of the supplied air-fuel mixture in accordance with the integral value, a stable operating state of the engine can be maintained even when the air-fuel ratio is made lean.

[0007]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows an internal combustion engine body to which an air-fuel ratio control device according to the present invention is applied. The internal combustion engine main body has four cylinders 1 to 4, and an intake pipe 16 and an exhaust pipe 17 are connected to each of the cylinders 1 to 4. The cylinder heads of the cylinders 1 to 4 are provided with in-cylinder pressure sensors 5 to 8 as in-cylinder pressure detecting means for detecting the pressure in the cylinders.

As shown in FIG. 2, each of the in-cylinder pressure sensors 5 to 8 has a sensor element portion 9 composed of a piezoelectric element,
And an amplification unit 10 for integrating (or averaging) and amplifying the voltage generated from the sensor element unit 9. As shown in FIG. 2, an ignition plug 13 is screwed into a screw hole 12 of each cylinder head 11 of the engine body, and is fixed to the ignition plug mounting seat surface 14 of the cylinder head 11 and its ignition plug washer portion 13a. The sensor element portion 9 of the in-cylinder pressure sensor is sandwiched together with the washer 15 and fixed by pressure.

The detection output of each of the in-cylinder pressure sensors 5 to 8 is EC
U (engine control unit) 21 is supplied. As shown in FIG.
PU31, ROM32, RAM33, A / D converter 3
4, at least a drive circuit 35 and a counter 37, which are connected to each other by a common bus. A /
The above-described in-cylinder pressure sensors 5 to 8 are connected to the D converter 34, and the four injectors 41 to 44 are connected to the drive circuit 35. The injectors 41 to 44 are provided in the intake pipe 16 in the vicinity of the intake port for each cylinder.
The fuel is injected by the driving operation of 5.

Other sensors are also connected to the A / D converter 34, for example, an intake pipe internal pressure sensor 39 for detecting the pressure in the intake pipe 16 downstream of a throttle valve (not shown), and cooling of the internal combustion engine. There are engine parameter sensors such as a cooling water temperature sensor 40 for detecting the water temperature T _W and a throttle opening sensor (not shown) for detecting the opening of the throttle valve. The A / D converter 34 uses the output pulse of the crank angle sensor 38 as the sampling timing. Since the crank angle sensor 38 generates a pulse each time the crankshaft rotates, for example, once, the A / D converter 34 synchronizes the analog output voltage of each sensor with the output pulse of the crank angle sensor 38 in a predetermined order. Is converted to a digital value and output for each sensor, and the digital value is repeatedly updated. The counter 37 measures the pulse generation interval output from the crank angle sensor 38 by counting the number of clock pulse generations, and generates a signal indicating the engine speed Ne. The crank angle sensor 38 generates a TDC signal indicating the top dead center of the piston of each cylinder together with a reference position signal indicating the time when the rotation angle of the crankshaft is at a predetermined angular position, and these are supplied to the CPU 31.

The CPU 31 of the ECU 21 performs a fuel injection control operation in synchronism with the TDC signal for each cylinder according to a program stored in the ROM 32 in order to supply fuel into the cylinders 1 to 4 of the engine by the injectors 41 to 44. . Since the same fuel injection control operation is performed for any of the cylinders, the fuel injection control operation for the cylinder 1 provided with the in-cylinder pressure sensor 5 will now be described.

In the fuel injection control operation, the CPU 31
First, as shown in FIG.
Fuel injection time Ti to engine speed Ne and intake pipe pressure
P_B(Step S1). Reference fuel injection
The firing time Ti is, for example, Ti stored in the ROM 32 in advance.
From the data map, engine speed Ne and intake pipe pressure P
_BThe search is set according to. The engine speed Ne is
The pressure P in the intake pipe obtained from the_BIs A / D conversion
Obtained from the vessel 34.

After setting the reference fuel injection time Ti, a net average effective pressure Pme is calculated based on the data of the in-cylinder pressure Pi for one cycle obtained from the in-cylinder pressure sensor 5 (step S2). The net average effective pressure Pme is a difference between the indicated average effective pressure Pmi and the pumping loss Pmf as shown in Expression (1).

[0014]

Pme = Pmi−Pmf (1) The indicated mean effective pressure Pmi is

[0015]

(Equation 2)

Is calculated as follows. Here, TDC is the cylinder volume at the top dead center position, and BDC is the cylinder volume at the bottom dead center position. DV is a cylinder volume change amount. The relationship between the in-cylinder pressure Pi and the cylinder volume V can be illustrated as shown in FIG. 5 in one cycle including intake, compression, explosion, and exhaust. The indicated mean effective pressure Pmi corresponds to the range indicated by the symbol A in FIG. Equation (2)
Corresponds to the area surrounded by 1-2-3-4-5-1 in FIG. 5, and the second integral term corresponds to 1-2-3'-4 'in FIG.
It corresponds to the area enclosed by -5-1.

The pumping loss Pmf is

[0018]

(Equation 3)

[0019]

It is calculated as follows. Pumping loss Pm
f corresponds to the range indicated by reference numeral B in FIG. The first integral term in equation (3) corresponds to the area surrounded by 1-2-3-6-1 in FIG. 5, and the second integral term is 1-2-3′-6′-1 in FIG. It corresponds to the area enclosed by. After calculating the net average effective pressure Pme, the CPU 31 sets a threshold value a (Ne) (step S3), and determines whether the net average effective pressure Pme is equal to or greater than the threshold value a (Ne) (step S4). The threshold value a (Ne) is set according to the engine speed Ne. For example, the threshold value a (Ne) is set smaller as the engine speed Ne is higher. This is because the higher the engine speed Ne, the better the engine combustion state is. If Pme ≧ a (Ne) as determined in step S4, the air-fuel ratio correction coefficient K _AF is reduced by a predetermined value (for example, 0.05) in order to make the air-fuel ratio of the supplied air-fuel mixture lean (step S4).
5). On the other hand, if Pme <a (Ne), the air-fuel ratio correction coefficient K _AF is increased by a predetermined value in order to enrich the air-fuel ratio of the supplied air-fuel mixture (step S6). Therefore, Pm
If the condition of e ≧ a (Ne) continues, the air-fuel ratio correction coefficient K _AF
Gradually decreases and if the state of Pme <a (Ne) continues, the air-fuel ratio correction coefficient K _AF gradually increases. Note that the initial value of the air-fuel ratio correction coefficient K _AF is 1.0.

After setting the air-fuel ratio correction coefficient K _AF , the CPU 31 calculates the fuel injection time Tp (step S).
7). The fuel injection time Tp is obtained by multiplying the reference fuel injection time Ti obtained in step S1 by the air-fuel ratio correction coefficient K _AF obtained in step S5 or S6 as Ti × K _AF . After calculating the fuel injection time Tp, a drive command for the fuel injection time Tp of the injector 41 is issued to the drive circuit 35 (step S8). The drive circuit 35 drives the injector 41 for a fuel injection time Tp from a specific point in time (for example, immediately before the intake stroke) in synchronization with the TDC signal to inject and supply fuel.

By performing such a fuel injection control operation, in the state of Pme ≧ a (Ne), the engine combustion is performed well without misfiring, and the air-fuel ratio of the supplied air-fuel mixture is made lean. Performs lean combustion. P
When the state of me <a (Ne) is detected, the air-fuel ratio is made rich so as not to cause misfire, and excessive leaning is prevented. If the combustion of the internal combustion engine is normal, the in-cylinder pressure during expansion in the explosion stroke is higher than that in the compression stroke, and the internal combustion engine performs a positive work. However, in the case of misfiring due to abnormal combustion, the line 5-4-3 in FIG. 5 is not substantially equal to or higher than the line 3'-4'-5,
The indicated average effective pressure Pmi is smaller than that during normal combustion. Therefore, by comparing the net average effective pressure Pme (or the indicated average effective pressure Pmi) with the threshold value, the air-fuel ratio can be made lean while preventing abnormal combustion. Also,
Since this fuel injection control operation is performed for each cylinder, proper lean combustion can be performed in any cylinder.

The execution of step S2 in this embodiment by the CPU 31 corresponds to the integration means, and
The execution of steps 3 to S8 by the CPU 31 and the drive circuit 35 and the injectors 41 to 44 correspond to air-fuel ratio adjusting means. In the embodiment described above, compared with the step S4 brake mean effective pressure Pme a threshold a (Ne), but sets the air-fuel ratio direction in accordance with the comparison result, the net mean effective pressure Pme _n calculated this time When one cycle compares the difference ΔPme the threshold α and (Ne) of the net mean effective pressure Pme _{n -1} calculated previously, may be set the air-fuel ratio direction in accordance with the comparison result. This threshold α (Ne) is set according to the engine speed Ne.

In the above-described embodiment, the net average effective pressure Pme is obtained as the integral value of the in-cylinder pressure detection signal. However, the indicated average effective pressure Pmi is compared with a threshold value, and the air-fuel ratio is determined according to the comparison result. The direction may be set. Further, in the above-described embodiment, the threshold value a (Ne) is set according to the engine speed Ne. However, the threshold value is set according to an engine parameter other than the engine speed, such as the throttle valve opening. Is also good.

[0025]

As described above, according to the present invention, the pressure in a cylinder of an internal combustion engine is detected, the detected pressure in the cylinder is integrated to obtain an integrated value, and the integrated value is supplied to the engine according to the integrated value. The air-fuel ratio of the air-fuel mixture is controlled. Therefore, since the combustion state of the engine can be determined from the integral value, by controlling the air-fuel ratio of the supplied air-fuel mixture in accordance with the integral value, the air-fuel ratio can be made lean while preventing misfiring, and stable. The maintained operating state of the engine can be maintained.

[Brief description of the drawings]

FIG. 1 is a diagram showing an internal combustion engine main body.

FIG. 2 is a diagram showing a configuration of an in-cylinder pressure sensor.

FIG. 3 is a block diagram illustrating a configuration of an ECU.

FIG. 4 is a flowchart showing an operation of a CPU in the ECU.

FIG. 5 is a diagram showing a relationship between in-cylinder pressure and cylinder volume.

[Description of Signs of Main Parts]

 1-4 cylinder 5-8 in-cylinder pressure sensor 16 intake pipe 17 exhaust pipe 21 ECU 38 crank angle sensor 39 intake pipe internal pressure sensor 40 cooling water temperature sensor 41-44 injector

Continuation of the front page (72) Inventor Kenji Nakano 1-4-1 Chuo, Wako-shi, Saitama Prefecture Honda Research Institute Co., Ltd. (72) Inventor Hiroaki Kato 1-4-1 Chuo, Wako-shi, Saitama Honda Co., Ltd. Inside the Technical Research Institute (72) Inventor Kenji Abe 1-4-1 Chuo, Wako-shi, Saitama Prefecture Inside Honda R & D Co., Ltd. (72) Inventor Hideyuki Oki 1-4-1 Chuo, Wako-shi, Saitama Honda Co., Ltd. In-house (72) Inventor Shunichi Tsuzuki 1-4-1 Chuo, Wako-shi, Saitama

Claims (4)

[Claims] 1. An in-cylinder pressure detection means for generating an in-cylinder pressure detection signal corresponding to a pressure in a cylinder of an internal combustion engine; an integration means for integrating the in-cylinder pressure detection signal to obtain an integral value; Air-fuel ratio control means for controlling the air-fuel ratio of the air-fuel mixture supplied to the engine. 2. The air-fuel ratio adjusting means leans the air-fuel ratio of the air-fuel mixture supplied to the engine when the integral value is equal to or greater than a threshold value, and supplies the air-fuel ratio to the engine when the integral value is smaller than the threshold value. The air-fuel ratio control device according to claim 1, wherein the air-fuel ratio of the air-fuel mixture is enriched. 3. The air-fuel ratio control device according to claim 2, wherein the threshold value is set smaller as the engine speed increases. 4. A pressure in a cylinder of the internal combustion engine is detected, an integrated value is obtained by integrating the detected pressure in the cylinder, and an air-fuel ratio of an air-fuel mixture supplied to the engine is controlled according to the integrated value. Air-fuel ratio control method.