JPH04140444A - Air-fuel ratio control device of engine - Google Patents

Abstract

PURPOSE:To surely prevent a misfire by detecting a relative difference of air- fuel ratio between one cylinder group and the other cylinder group, and feedback controlling air-fuel ratio of an intake system of the cylinder group, whose air- fuel ratio relatively shows a lean direction, to absolute lean air-fuel ratio. CONSTITUTION:In a 6-cylinder V-engine provided with three cylinders 4 in each right/left bank 2, 3, signals from various sensors are received to a control unit U to perform air-fuel ratio feedback control. In the control by this control unit U, target air-fuel ratio is set to theoretical air-fuel ratio in both the right/ left banks 2, 3 for a predetermined period just after starting engine operation, and a feedback correction amount is studied based on corresponding linear O2 sensors 27, 28 relating to each bank 2, 3. Under comparison of study values of each bank 2, 3, for the bank of large study value, that is, for the bank relatively in a lean tendency, the target air-fuel ratio is made lean, and the feedback control is performed based on this lean target air-fuel ratio.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an air-fuel ratio control device for an engine, and more particularly to lean burn control.

(Prior art) As seen in Japanese Patent Application Laid-open No. 59-208141, O
A linear 02 sensor that linearly detects the oxygen concentration in exhaust gas is known as a z sensor. The same publication also discloses lean burn control in which the air-fuel ratio of the engine is feedback-controlled to an absolute lean state, such as A/F=20, using the linear 02 sensor. Regarding this lean burn control, for example, in a V-type engine in which cylinders in one group and cylinders in another group are arranged in a V-shape, one group of cylinders (one bank) is controlled under the stoichiometric air-fuel ratio. It is known to perform lean burn control on other cylinder groups (other banks) under an absolute lean air-fuel ratio. That is, in a V-type engine, the ignition order is usually one bank and then the other bank, so that one bank and the other bank are ignited alternately.
Therefore, by setting one bank to the stoichiometric air-fuel ratio and setting the other bank to lean burn, there is an advantage that fuel efficiency can be improved by lean burn while suppressing variations in rotation.

(Problems with the Prior Art) However, when such a method is used, the premise is that one bank and the other bank are provided with independent intake systems and fuel supply means, respectively. This may cause variations in the relative air-fuel ratio between one bank and another bank depending on the layout of the engine intake system or the characteristics of the injector as a fuel supply means. Taking an injector as an example, there are variations in the amount of injection between individual injectors due to manufacturing tolerances. If an injector with a large injection amount (hereinafter referred to as a rich injector) is disposed in one bank, this one bank will have a rich tendency characteristic. On the other hand, when injectors c and below, which have a small injection amount (referred to as lean injectors), are arranged in one bank, this one bank has a lean tendency characteristic.

For such variations in air-fuel ratio propensity between banks,
For example, when the lean burn control described above is applied to a bank that tends to be rich, more fuel will be supplied, and the correction of this fuel supply will be performed in the lean direction. However, since the correction in the lean direction is a correction in the direction of decreasing the supplied fuel in the J-burner, which is inherently prone to misfires, there is a strong possibility that misfires will occur.

Therefore, an object of the present invention is to focus on the fact that the tendency of the air-fuel ratio often differs between banks, for example, in the case of type III engines, and to actively utilize the difference in the tendency of the air-fuel ratio, An object of the present invention is to provide an air-fuel ratio control device for an engine that suppresses the risk of misfire in lean burn control.

(Means for Solving the Problems) In order to achieve this technical problem, in the first invention of the present invention, a multi-cylinder engine is provided with one group of cylinders and another group of cylinders. The one cylinder group and the other cylinder group are each provided with an independent intake system and fuel supply means, and the one cylinder group and the other cylinder group are An air-fuel ratio detection means for detecting a relative difference in air-fuel ratio between the one cylinder group and another cylinder group; The lean burn control means receives a signal from the means and feedback-controls the air-fuel ratio of the intake system of the cylinder group whose air-fuel ratio tends to be relatively lean to an absolute lean air-fuel ratio.

That is, a group of cylinders exhibiting a lean tendency is detected, and lean burn control is applied to the cylinder group exhibiting a lean tendency. According to this, compared to when lean burn control is applied to a cylinder group that exhibits a tendency to be rich, the fuel supply correction will be made in the rich direction (increasing the amount of supplied fuel). .

Furthermore, in the second aspect of the present invention, the multi-cylinder engine is classified into one group of cylinders and another group of cylinders, and these one cylinder group and the other cylinder group include: Assuming that the engine air-fuel ratio control device is provided with an independent intake system and a fuel supply means and performs lean burn control so that only one cylinder group has an absolute lean air-fuel ratio, An injector with a lean tendency selected in advance is used as a fuel supply means for a cylinder group that is controlled to have a lean air-fuel ratio, a linear 02 sensor is provided in an exhaust system of the cylinder group, and the linear 02 sensor is provided in the exhaust system of the cylinder group. In response to a signal from the 02 sensor, feedback control is performed so that the air-fuel ratio of the intake system of the first cylinder group becomes an absolute lean air-fuel ratio.

That is, an injector having a lean tendency is selected in advance, and this lean injector is arranged in a cylinder group to be subjected to lean burn control. According to this, the cylinder group subject to lean burn control exhibits a lean tendency, and the fuel supply is corrected in the rich direction.

(Example) Hereinafter, an example of the present invention will be described based on the accompanying drawings.

In Fig. 1, l is the engine body, and engine body 1
It is said to be a type 6-cylinder engine with a left bank 2 and a right bank 3, and each bank 2.3 has three cylinders 4. Each cylinder 4 is equipped with a piston 6 that reciprocates up and down within the cylinder pore 5, and an intake boat 8 and an exhaust boat 9 are opened facing a combustion chamber 7 defined by the piston 6. An intake valve 10 is disposed, and an exhaust valve 11 is disposed on the exhaust boat 9, and both valves 101 and 11 are opened and closed at predetermined timing.

The intake passage 12 connected to each intake boat 8 of the engine main body 1 has a common intake pipe 13,
The surge tank 14 is formed by independent intake pipes 15, 16, one independent intake pipe 15 is connected to each intake boat 8 of the left bank 2, and the other independent intake pipe 16 is connected to each intake boat 8 of the right bank 3. has been done. In the intake passage 12,
An air cleaner 17 is disposed at the upstream end of the common intake pipe 13, and a throttle valve I8 as an output control valve is disposed at the downstream side of the common intake pipe 13.
An air flow meter 19 is disposed between the air cleaner 17 and the air cleaner 17 . Further, injectors 20 and 21 are arranged for each cylinder 4 so as to face the intake boat 8 of each cylinder 4.

The exhaust passage 22 connected to each exhaust boat 9 of the engine body 1 has two independent exhaust pipes 23 connected to each exhaust boat 9 of the left bank 2 and another independent exhaust pipe 23 connected to each exhaust boat 9 of the right bank 3. an independent exhaust pipe 24; and these independent exhaust pipes 23.
A three-way catalyst 26 for exhaust gas purification is disposed in this common exhaust pipe 25, and each of the independent exhaust pipes 23 and 24 has a common exhaust pipe 25. 02 sensors 27 and 28 are respectively arranged.

In FIG. 1, reference numeral U is a control unit composed of, for example, a microcomputer, and the control unit U includes the air flow meter 19.02 sensor 27.2.
A signal from sensor 8 is inputted, and signals from sensors 29 to 31 are also inputted. The air flow meter 19 is for detecting the amount of intake air. The 0□ sensors 27 and 28 detect the oxygen concentration in the exhaust gas, and are linear 02 sensors that linearly output signals in accordance with the oxygen concentration. The sensor 29 detects the engine cooling water temperature. The sensor 30 detects the opening degree of the throttle valve 18 (throttle opening degree). The sensor 3I detects the engine rotation speed from the rotation speed of the crankshaft 32.

The control unit U receives signals from these various sensors and performs air-fuel ratio feedback control.

To explain the outline of the control by this control unit U, for a predetermined period immediately after the start of engine operation, the target air-fuel ratio is the stoichiometric air-fuel ratio for both the left and right banks 2.3.
= 14.7, learning of the feedback correction amount based on the corresponding linear 02 sensor 27.28 is performed for each bank 2.3, and then the learning value of left bank 2 and the learning value of right bank 3 are Based on the comparison, for bank 5 with a large learning value, that is, a bank with a relatively lean tendency, its target air-fuel ratio is set to lean, and feedback control is performed based on this lean target air-fuel ratio. It has become.

Based on the above premise, a detailed explanation will be given based on the flowcharts shown in FIGS. 2 and 3.

First, after inputting various information in step Sl (hereinafter, the step number is indicated by the symbol "S"),
Proceeding to step 2, the basic injection pulse width Ce for the injectors 20 and 21 is calculated based on the following formula.

Here, Qa miko intake air amount N: engine rotational speed At the next step 83, it is determined whether or not sampling of the feedback correction amount Cfb, which will be described later, has been performed n times. Immediately after the engine starts, the answer is NO, so the process advances to S4, where the target air-fuel ratio for both the left and right banks 2.3 is set to the stoichiometric air-fuel ratio (A/F=14.7), and then the linear 02 sensor 27. 28 detection signal reading (S5
), then the feedback correction amount Cfb is calculated based on the linear 02 sensor 27.28 corresponding to each bank 2.3 (S6), and then in S7, the learning value clarn of the feedback correction amount Cfb is calculated as follows. This is done based on the formula.

Here clran: Current learning value clran (n -1): Previous learning value nCfb
: Cumulative value of Cfb n times n: Number of samples Then, in S8, the final injection pulse width is determined by a known method such as adding the feedback correction amount Cfb to the basic injection pulse width Ce, and is calculated for each injector 20.
．． Checking the injection timing of 21 (S9), the injection of injectors 20 and 21 is executed (SIO).

The sampling of Cfb of the feedback correction amount is n
After the process is repeated, the answer is YES in S3, and the process proceeds to Sll, where a lean target air-fuel ratio is set.

That is, as shown in FIG. 3, after reading the learning values clran of the right bank 3 and left bank 2 (S12
．． 513), and based on the comparison of these learned values, it is determined whether or not the right bank 3 tends to be relatively lean (S14). That is, as shown in FIG. 4, if the learned value clran of the right bank 3 is larger than the learned value clran of the left bank 2, it is assumed that the right bank 3 is in a lean tendency, and the process proceeds to S15. Set the target air-fuel ratio of bank 3 to, for example, A/F based on the map shown in FIG.
A lean target air-fuel ratio is set, such as F=21.0. On the other hand, when the left bank 2 tends to be relatively lean, the process proceeds from S14 to S16, where the target air-fuel ratio of the left bank 2 is set to be lean.

Thereafter, feedback control of the right bank 3 or the left bank 2 is performed based on this lean target air-fuel ratio (S17.318, etc.). In this case, in principle, the stoichiometric air-fuel ratio is set as the target air-fuel ratio for the relatively rich bank, and feedback control is performed under this air-fuel ratio.

The drawings after FIG. 6 show a second embodiment of the present invention.

In this example, we focused on the fact that lean injectors and rich injectors exist within the manufacturing tolerance range of injectors, as shown in Figure 6, and classified lean injectors and notch injectors in advance. Therefore, the lean injector is arranged in the right bank 3, while the rich injector is arranged in the left bank 2. That is, in FIG. 1, the left bank 2 injector 20 is a rich injector, and the right bank 3 injector 20 is a rich injector.
The injector 21 is a lean injector. Regarding the Oz sensor, an 02 sensor that outputs a binary signal across the stoichiometric air-fuel ratio and a linear 02 sensor are prepared, and the sensor 27 for the left bank is the 02 sensor, and the sensor 28 for the right bank 3 is used as the 02 sensor. is considered to be a linear 02 sensor.

FIG. 7 shows the injector classification process. That is, the injector is installed in the engine, the target air-fuel ratio of the engine is set to the stoichiometric air-fuel ratio, and then the engine is actually operated (PL), the detection signal from the linear 02 sensor is read (P2), and the air-fuel ratio is calculated from the stoichiometric air-fuel ratio. Detect deviation (deviation) (P3). Then, based on this deviation, the unique characteristics of the injector are determined (P4), and injectors whose actual injection amount is injected in winter are classified as rich injectors, and conversely, injectors that are injected with a small amount are classified as rich injectors. are selected as lean injectors.

FIG. 8 shows the content of feedback control for the left bank 2 equipped with a rich injector. That is, basically the same processing as in FIG. 2 is performed, but in calculating the basic injection pulse width at 323, the basic pulse width is adjusted so that the air-fuel ratio of left bank 2 becomes the stoichiometric air-fuel ratio. Setting of Ce is performed.

FIG. 9 shows the content of feedback control for the right bank 3 equipped with a lean injector. here,
The target air-fuel ratio in S33 is set based on the map shown in FIG.
8 performs lean burn feedback control.

In this embodiment, for the right bank 3 where lean burn control is performed, the feedback correction value Cfb
As a result, a correction value (positive value) in the rich direction is guaranteed. In other words, in lean burn control where misfires are likely to occur, it can be guaranteed that the correction will be made in a direction that avoids misfires. Note that for the left bank 2, a rich injector is employed in this embodiment, but an injector that tends to be richer than at least the lean injector employed for the right bank 3 may be employed.

(Effects of the Invention) As is clear from the above description, according to the present invention, in lean burn control, the correction is guaranteed in the rich direction, so that the risk of engine misfire can be suppressed.

[Brief explanation of drawings]

FIG. 1 is an overall system diagram of the embodiment. 2 to 5 show the first embodiment. FIGS. 2 and 3 are flowcharts showing an example of control, FIG. 4 is an explanatory diagram showing learning values of feedback correction values, and FIG. 5 is a map regarding control target values of lean burn control. 6 to 9 show the second embodiment, in which FIG. 6 is an explanatory diagram showing the range of manufacturing error of the injector, FIG. 7 is a process diagram showing the injector selection process, and FIGS. 8 and 9. The figure is a flowchart showing an example of control. 1: Engine body 2: Left bank 3: Right bank 13: Common intake passage 15: Independent intake passage 16: Independent intake passage 19: Air flow meter 20: Injector 21: Injector 23: Independent exhaust pipe for left bank 24: For right bank Independent exhaust pipe 27: Air-fuel ratio sensor for left bank 28: Air-fuel ratio sensor for right bank U: Control unit (V-type engine)

Claims (2)

[Claims] (1) A multi-cylinder engine is classified into one group of cylinders and another group of cylinders, and each of these one cylinder group and the other cylinder group is provided with an independent intake system and fuel supply means. The first cylinder group and the other cylinder group are used to control the relative relationship between the first cylinder group and the other cylinder group in an engine air-fuel ratio control device in which air-fuel ratio feedback control is performed independently. an air-fuel ratio detecting means for detecting a difference in air-fuel ratio; and an air-fuel ratio detecting means for detecting a difference in air-fuel ratio; An air-fuel ratio control device for an engine, comprising: a lean-burn control means for performing feedback control on the air-fuel ratio; (2) A multi-cylinder engine is classified into one group of cylinders and another group of cylinders, and each of these one cylinder group and the other cylinder group is provided with an independent intake system and fuel supply means. In an air-fuel ratio control device for an engine that performs lean burn control so that only one cylinder group has an absolute lean air-fuel ratio, the first cylinder group that is controlled to have an absolute lean air-fuel ratio An injector with a preselected lean tendency is used as the fuel supply means, a linear O_2 sensor is provided in the exhaust system of the one cylinder group, and in response to a signal from the linear O_2 sensor, the first cylinder group An air-fuel ratio control device for an engine, characterized in that the air-fuel ratio of an intake system of an engine is feedback-controlled so that it becomes an absolute lean air-fuel ratio.