JPH0249948A - Air-fuel ratio control device for engine - Google Patents

Abstract

PURPOSE:To improve purifying performance of exhaust in a catalyst by correcting air-fuel ratio in one of the cylinder groups in accordance with an output of the third air-fuel ratio sensor provided in a common exhaust passage, in the case of an engine which performs a feedback control of the air-fuel ratio in every cylinder group divided into two parts. CONSTITUTION:The first and second O2 sensors 15, 16 are provided in exhaust passages 13, 14 of each cylinder group divided into two parts, and being based on an output of these sensors, a feedback control of each fuel injection valve 10, 11 is performed by an ECU20 in order that air-fuel ratio of each group respectively approaches the target air-fuel ratio. Here each exhaust passage 13, 14 is collected in the downstream side of the O2 sensors 15, 16, forming a common exhaust passage 17, and a catalytic converter 18 is provided interposing halfway the passage 17. While in the upstream side part of the catalytic converter 18 in the common exhaust passage 17, the third O2 sensor 19, detecting the exhaust gas from each exhaust passage 13, 14 for its air-fuel ratio deflected from the target air-fuel ratio, is provided, and the air-fuel ratio in at least one of the cylinder groups is corrected being based on an output of the third O2 sensor 19.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an engine air-fuel ratio control device that performs feedback control of an air-fuel ratio for each cylinder group of a multi-cylinder engine divided into two cylinder groups.

(Prior art) Conventionally, in a ■-type multi-cylinder engine such as a ■6-type engine, an air-fuel ratio sensor such as a 0□ sensor is provided in the common exhaust passage downstream from the gathering point of the exhaust passages of both banks, and A catalytic converter is installed downstream of this air-fuel ratio sensor to purify the exhaust gas, but since the air-fuel ratio sensor is located far from the engine exhaust boat, the temperature of the exhaust gas is low. There is a problem that the air-fuel ratio decreases, causing a response delay in the air-fuel ratio sensor, and there is also a drawback that the air-fuel ratio varies between banks. Therefore, for example, as disclosed in Japanese Patent Application Laid-Open No. 60-190630,
An air-fuel ratio sensor is installed in each exhaust passage provided for each cylinder group belonging to each bank.
An air-fuel ratio control system is employed that performs air-fuel ratio feedback control independently for each of the two banks. By performing this type of air-fuel ratio control, the air-fuel ratio sensor can be exposed to high-temperature exhaust gas, and accurate air-fuel ratio control can be performed for each bank, thereby increasing the exhaust gas purification ability of the catalytic converter. Can be done.

However, due to variations in the characteristics and differences in the degree of deterioration of the air-fuel ratio sensors installed in the exhaust passages of both banks, a difference occurs in the total air-fuel ratio in the common exhaust passage, and the exhaust gas purification performance of the catalyst deteriorates. This has caused the problem of deterioration of emission characteristics.

(Object of the Invention) The present invention provides exhaust gas purification by the catalyst by making the air-fuel ratio of the exhaust gas flowing into the catalyst equal to the stoichiometric air-fuel ratio when air-fuel ratio control is performed for each two cylinder groups as described above. An object of the present invention is to provide an air-fuel ratio control device for an engine that can improve performance.

(Structure of the Invention) According to the present invention, two exhaust passages each provided with an air-fuel ratio sensor are brought together on the downstream side of the air-fuel ratio sensor to form a common exhaust passage, and exhaust gas is introduced into the common exhaust passage. A catalyst device for purification is provided, and the average air-fuel ratio of the exhaust gas discharged from the two exhaust passages is provided in a portion of the common exhaust passage between the gathering part of the two exhaust passages and the catalyst device. A third air-fuel ratio sensor is provided to detect a deviation from the target air-fuel ratio, and the air-fuel ratio of at least one cylinder group is corrected based on the detection of the deviation by the third air-fuel ratio sensor. shall be.

(Effects of the Invention) According to the present invention, the air-fuel ratio of the exhaust gas flowing into the catalyst can be made substantially equal to the stoichiometric air-fuel ratio, thereby ensuring the exhaust gas purification performance of the catalyst.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 is an overall schematic diagram showing an embodiment of an engine control device according to the present invention. In Figure 1, the engine body 1
For example, six cylinders are arranged in two rows in a character shape to form a left bank 2L and a right bank 2R, and each bank 2
Three cylinders belonging to L and 2R each form a first cylinder group and a second cylinder group. An air flow meter 4 is provided upstream of the common intake passage 3, a throttle valve 5 and a surge tank 6 are provided downstream of the air flow meter 4, and independent intake passages 7.8 branched from the surge tank 6 are connected to each bank. They are connected to the 2L and 2R cylinder groups, respectively. Each independent intake passage7.
8 is provided with fuel injectors 10 and 11 for supplying pressurized fuel from the fuel supply system to the intake boat through the fuel pipe 9 for each cylinder.

On the other hand, exhaust passages 13.14 are independently connected to each bank 2L, 2R, and these exhaust passages 13.
14 is a 0□ sensor 15.16 as an air-fuel ratio sensor.
are arranged respectively, and the exhaust passages 13 and 14 are arranged in the above 0□
They merge downstream of the sensors 15 and 16 to form a common exhaust passage 17.
is formed. This common exhaust passage 17 is provided with a three-way catalytic converter 18 that simultaneously purifies the three harmful components HC, Co, and NOX in the exhaust gas. A 0□ sensor 19 as a third air-fuel ratio sensor is disposed between the catalytic converter 18 and the catalytic converter 18 .

In the above configuration, the 02 sensor 15.16 that generates an electrical signal according to the oxygen concentration in the exhaust gas has a sudden change in output value near the stoichiometric air-fuel ratio (λ=1), as shown in Figure 2. , and the control circuit 20 controls these 0□ sensors 15.1
Based on the output of 6 and the outputs from the air flow meter 4, engine speed sensor, water temperature sensor, throttle opening sensor with idle switch, and other various sensors,
The pulse width Ti of the fuel injection control signal for the fuel injector 10.11 is calculated, and air-fuel ratio feedback control is performed for each bank 2L, 2R.

In this case, the control circuit 20 controls the 0□ sensor 15.16.
Judgment level a (slice level), which serves as a criterion for air-fuel ratio changes in the rich direction and lean direction, is set approximately at the center of the output change range, and the output curve of the O2 sensor 15.16 The time when the output curve crosses from the rich side to the rich side is defined as the lean detection time, and the time when the output curve crosses the determination level a from the rich side to the lean side is defined as the lean detection time. Furthermore, fuel injector 10.11 to 0! Sensor 15.
Combustion gas transmission delay up to 16, and O□ sensor 15
．． In order to compensate for the response delay etc. of the 16 itself, the 02 sensor 15
．． Delay times TDL and T are provided from when the output of No. 16 crosses the above-mentioned judgment level a and reverses to rich-lean or lean-rich until the air-fuel ratio change control starts, and when the lean delay time TDL has elapsed. The period from when the rich delay time TD,l has elapsed is set as the period when the air-fuel ratio control flag F=1, and the air-fuel ratio is controlled to the lean side. In the air-fuel ratio control signal waveform shown in FIG. 2, P is a proportional value, and ■ is an integral factor that determines the slope of the control signal waveform.

Further, in the control circuit, 20 is a third air-fuel ratio sensor 0.
□The sensor 19 detects the deviation amount of the actual air-fuel ratio A of the exhaust gas in the common exhaust passage 17 from the target air-fuel ratio V, and based on the detection of this deviation amount, both banks 2
The delay times T and T in the air-fuel ratio feedback control in L and 2R or the feedback control value are corrected so that the air-fuel ratio of the exhaust gas flowing into the catalyst device 18 becomes the stoichiometric air-fuel ratio.

Next, the air-fuel ratio control executed by the control circuit 20 will be explained with reference to the flowchart of FIG. 3.

First, in step S1, based on the throttle opening signal output from the throttle opening sensor and the engine rotation speed signal output from the engine rotation speed sensor,
It is determined whether the operating region is in the air-fuel ratio feedback control region of low and medium load regions, and if it is in the feedback region, the process proceeds to step s2 and executes the main routine of feedback control using the 02 sensor 15.16. . Then, in the next step S3, the output of the third 02 sensor 19, which indicates the actual air-fuel ratio A in the common exhaust passage 17, is read. Next, in step S4, this air-fuel ratio A is changed to the target air-fuel ratio ■.
If A>V, the air-fuel ratio has deviated to the rich side, so proceed to step S5, and calculate the value T□-M obtained by subtracting the predetermined delay correction time M from the rich delay time TD,l. is determined, and if Tom M2O, the rich delay time Tfl+t is changed to T□-M in step S6. Also, if To or -Mho, step S
Change the lean delay time TDL side at 7 to TDL+
Let it be M.

On the other hand, if it is determined in step S4 that A<V, the air-fuel ratio has deviated to the lean side, so step S8
The process proceeds to step S9 to determine the value TDLM obtained by subtracting a predetermined delay correction time M from the lean delay time T0°, and if TILL M2O, the lean delay time TDL is changed to TDLM in step S9. Also, T.D.
If LM<O, the rich delay time TIIR side is changed to Tel+M in step 310.

The above processing is repeatedly executed until it is determined in step Sll that the engine has stopped, but if the determination result in step S1 is
If NOj, open control is performed in step 312.

The process shown in the flowchart of FIG. 3 explained above corrects the deviation in the air-fuel ratio of the exhaust gas flowing into the catalyst by changing the rich delay time TDR or the lean delay time TDL. Next, the processing of Step 7 S2, which is the feedback control main routine based on the changed delay times TDII and Tot, will be explained with reference to the flowchart of FIG.

First, in step S21, the actual air-fuel ratio A from the O2 sensor 19 is read, and in step 322, this actual air-fuel ratio A is compared with the target air-fuel ratio (■), and A>V.

If the air-fuel ratio is rich in step 323, the previous air-fuel ratio A' is further compared with the target air-fuel ratio V, and A'>V.
, if the previous time was also rich, it is determined in step S24 whether the air-fuel ratio flag F is 1 or not, and if F=1, the integral value ΔI is subtracted from the feedback control value in the next step S25, and the air-fuel ratio flag is determined to be empty. Control the fuel ratio to the lean side. Also, A′≦V
If F was lean last time, a lean delay time TDL timer is set in step 326, and in the next step S27 it is determined whether or not the lean delay time TDL has time-amplified. During this period, the lean delay time is subtracted in step 328, and the integral value Δ■ is added to the feedback control value in step S29.
is added to control the air-fuel ratio to the rich side. When the lean delay time TDL is up, step S
In step 30, the air-fuel ratio flag F is set to 1 to perform rich determination, and in step 331, the proportional value P is subtracted from the feedback control value. Thereafter, in step S32, the current air-fuel ratio A is set as the previous air-fuel ratio A' and the process ends.

On the other hand, if it is determined in step S22 that A≦vF and the air-fuel ratio is lean, then in step S33 the previous air-fuel ratio A' is compared with the target air-fuel ratio ■, and if A'<V, the previous air-fuel ratio is also lean. In this case, the air-fuel ratio flag F is set to 0 in step S34.
If F=0, the integral value Δ■ is added to the feed bank control value in step 335 to control the air-fuel ratio to the rich side. In addition, if A'≧■ and the previous time was rich, the rich delay time TD is determined in step 336.
1 timer is set, and in the next step S37 it is determined whether or not the rich delay time To11 has timed up. If this determination is rNOJ, the rich delay timer is subtracted in step 338, and the rich delay timer is subtracted in step S39.
The integral value ΔI is subtracted from the feed bank control value to control the air-fuel ratio to the lean side. Rich Daytime Ti
, , is time amplified, the process proceeds to step 340, where the air-fuel ratio flag F is set to 0 and a lean determination is made, the proportional value P is added to the feedback control value in step S41, and the proportional value P is added to the feedback control value in step S41. The process ends with the current air-fuel ratio A being set as the previous air-fuel ratio A'.

In addition, in the above-mentioned embodiment, the delay time To Tl1
Although the correction of ll or the correction of the feedback control value is performed for both banks 2L and 2R, the correction may be performed for at least one bank only.

[Brief explanation of the drawing]

FIG. 1 is an overall schematic diagram of an embodiment of the present invention, FIG. 2 is a diagram showing the relationship between the output of the air-fuel ratio sensor and the air-fuel ratio feedbank control signal, and FIGS. It is a flowchart of fuel ratio feed bank control. - Engine body, 2R - Left and right bank common intake passage 7.8 - Independent intake passage 0.11 - Fuel injector 3.14 - Exhaust passage 5.16.19 - Of sensor 7... - Common exhaust passage 18...Catalytic converter 0
−Control circuit

Claims (1)

[Claims] In a multi-cylinder engine divided into two cylinder groups, a first air-fuel ratio sensor is disposed in the exhaust passage of one cylinder group, and a second air-fuel ratio sensor is disposed in the exhaust passage of the other cylinder group. In the air-fuel ratio control device for an engine, the air-fuel ratio control device for an engine is configured to perform feedback control to bring the air-fuel ratio of a corresponding cylinder group closer to a target air-fuel ratio based on the outputs of the first and second air-fuel ratio sensors. Two exhaust passages each provided with a first and second air-fuel ratio sensor are assembled on the downstream side of the air-fuel ratio sensor to form a common exhaust passage, and a catalyst device for purifying exhaust gas is installed in the common exhaust passage. is provided in a portion of the common exhaust passage between the gathering part of the two exhaust passages and the catalyst device, the average air-fuel ratio of the exhaust gas discharged from the two exhaust passages is set to the target air-fuel ratio. An engine characterized in that a third air-fuel ratio sensor is provided for detecting the deviation, and the air-fuel ratio of at least one cylinder group is corrected based on the detection of the deviation by the third air-fuel ratio sensor. Air-fuel ratio control device.