JP5004935B2 - Air-fuel ratio control method for internal combustion engine - Google Patents

Description

  The present invention relates to an air-fuel ratio control method for an internal combustion engine that controls an air-fuel ratio based on an output of an oxygen sensor provided in an exhaust passage.

2. Description of the Related Art In recent years, for example, internal combustion engines for automobiles use a NOx occlusion type catalyst (hereinafter abbreviated as a catalyst), which is a catalyst having an improved ability to occlude NOx in exhaust gas in order to purify the exhaust gas. . In an internal combustion engine using such a catalyst, the active state of the catalyst is determined based on the temperature of the catalyst, for example, as described in Patent Document 1, and if it is determined that the catalyst is inactive, the air-fuel ratio is stoichiometric. Alternatively, an air-fuel ratio control device configured to correct a target air-fuel ratio so as not to become rich is known.
Japanese Patent Laid-Open No. 11-36968

  By the way, with the above-described configuration, even if the target air-fuel ratio is corrected so as not to become stoichiometric or rich when the catalyst is inactive, most of the NOx is not occluded in the catalyst. Is discharged. If the operation is continued in such an air-fuel ratio control state without cutting the fuel to stop the fuel supply, the amount of oxygen stored in the catalyst is not sufficient. As a result, the purification rate of HC and CO in the exhaust gas may decrease.

  Therefore, the present invention aims to eliminate such problems.

  That is, the air-fuel ratio control method for an internal combustion engine according to the present invention is an internal combustion engine including a catalyst provided in the exhaust passage and an oxygen sensor provided upstream of the catalyst, after detecting that the oxygen sensor is activated. An air-fuel ratio control method for an internal combustion engine that controls an air-fuel ratio using an air-fuel ratio correction constant set based on an output of an oxygen sensor, wherein the supply of fuel is stopped after detecting that the oxygen sensor is activated As a fuel cut history, and when there is no fuel cut history record, a predetermined air-fuel ratio correction constant is selected so that the air-fuel ratio becomes leaner than when there is a fuel cut history record. To do.

  According to such a configuration, when the supply of fuel is stopped after the oxygen sensor is activated, this is recorded as a fuel cut history. In the case where the fuel cut history is not recorded in the activation after activation of the oxygen sensor, and there is a state where oxygen in the catalyst becomes extremely small, the air-fuel ratio correction constant is set to be more empty than in the case where there is a fuel cut history. By selecting the fuel ratio to be lean, it becomes possible to promptly activate the catalyst.

  The present invention is configured as described above, and the air-fuel ratio correction constant is set when the supply of fuel is not stopped after the activation of the oxygen sensor, and there is a situation where oxygen in the catalyst becomes extremely low. By selecting the air-fuel ratio to be leaner than when there is a cut history, it is possible to promptly activate the catalyst.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

The engine 100 schematically shown in FIG. 1 is of a spark ignition type four-cycle four-cylinder for an automobile, which is representatively shown in the configuration of one cylinder. An intake system 1 of the engine 100 is provided with a throttle valve 2 that opens and closes in response to an accelerator pedal (not shown), and a surge tank 3 is provided downstream thereof. A fuel injection valve 5 is further provided in the vicinity of one end communicating with the surge tank 3, and the fuel injection valve 5 is controlled by the electronic control unit 6. The cylinder head 8 forming the combustion chamber 7 is provided with an intake valve 9 and an exhaust valve 10 and a spark plug 11 that generates a spark. Further, the exhaust system 12 is provided with a three-way catalyst 14 as a catalyst in an exhaust pipe 13 leading to a muffler (not shown), and a signal for controlling the air-fuel ratio by measuring the oxygen concentration in the exhaust gas. A main O ₂ sensor 15 as an oxygen sensor to be output is disposed at a position upstream of the three-way catalyst 14, and a sub O ₂ sensor 16 as detection means for detecting the air-fuel ratio is also downstream of the three-way catalyst 14. It is arranged. The main O ₂ sensor 15 and the sub O ₂ sensor 16 output a binary output signal h in accordance with the oxygen concentration in the exhaust gas, that is, the air-fuel ratio. The main O ₂ sensor 15 and the sub O ₂ sensor 16 of this embodiment are each provided with a heater to promote activation, and are configured to be energized to the heater at the same time as the engine 100 is started. .

The electronic control device 6 is mainly configured by a microcomputer system including a central processing unit 17, a storage device 18, an input interface 19, and an output interface 20. The input interface 19 has an intake pressure signal a output from an intake pressure sensor 21 for detecting the pressure in the surge tank 3, that is, an intake pipe pressure, and an output from a cam position sensor 22 for detecting the rotation state of the engine 100. Cylinder discrimination signal G1, crank angle reference position signal G2, engine speed signal b, vehicle speed signal c output from the vehicle speed sensor 23 for detecting the vehicle speed, idle switch for detecting the open / closed state of the throttle valve 2 IDL signal d output from 24, water temperature signal e output from water temperature sensor 25 for detecting the cooling water temperature of engine 100, output signal (voltage signal) h output from main O ₂ sensor 15 described above, sub signal An output signal (voltage signal) k or the like output from the O ₂ sensor 16 is input. On the other hand, the output interface 20 is configured to output a fuel injection signal f to the fuel injection valve 5 and an ignition pulse g to the spark plug 11.

  The electronic control device 6 has various information determined according to the operating state of the engine 100 using the intake pressure signal a output from the intake pressure sensor 21 and the rotation speed signal b output from the cam position sensor 22 as main information. The basic injection time (basic injection amount) is corrected by the correction coefficient to determine the fuel injection valve opening time, that is, the final injector energization time T, and the fuel injection valve 5 is controlled based on the determined energization time to correspond to the engine load. A program for injecting fuel into the intake system 1 is incorporated. As a correction coefficient for correcting the basic injection amount, an intake air temperature correction coefficient for increasing in accordance with the intake air temperature, a feedback correction coefficient FAF when feedback control of the air-fuel ratio is performed, and a power increase correction coefficient when output is requested and so on.

When the air-fuel ratio feedback control is executed in a state where the engine 100 is warmed up and the main O ₂ sensor 15 and the sub O ₂ sensor 16 are fully activated, the actual air-fuel ratio is almost theoretical. For example, as shown in FIG. 2, the feedback correction coefficient FAF is changed in accordance with the output signal h from the main O ₂ sensor 15 so as to be close to the air-fuel ratio.

That is, when the output signal h of the main O ₂ sensor 15 exceeds the determination value and a rich state is detected, the feedback correction coefficient FAF is gradually decreased in the direction of decreasing the fuel using a predetermined integration constant KIM. I will let you. On the other hand, when the output signal h of the main O ₂ sensor 15 is below the determination voltage and the lean state is detected, the feedback correction coefficient is obtained when the delay time TDL elapses after the output signal h reaches the determination voltage. The FAF is skipped to the side where the fuel is increased by a fixed skip value RSP, and then the feedback correction coefficient FAF is increased to the side where the fuel is increased using a predetermined integral constant KIP. Furthermore, when the main O ₂ sensor 15 detects a rich state as a result of increasing the fuel, the feedback is performed after a predetermined delay time TDR has elapsed from the time when the output signal h of the main O ₂ sensor 15 exceeds the determination voltage. The correction coefficient FAF is skipped to the side where the fuel is reduced by a fixed skip value RSM, and then the feedback correction coefficient FAF is reduced to the side where the fuel is reduced using a predetermined integration constant KIM. The actual operation of the air-fuel ratio is made closer to the stoichiometric air-fuel ratio by repeatedly executing the above operation on the feedback correction coefficient FAF.

In this embodiment, the integration constants KIM and KIP and the skip values RSP and RSM are set to constant values among the air-fuel ratio correction constants described above, but the main O ₂ sensor 15 is completely activated. Thereafter, the delay times TDR and TDL are changed in accordance with the output signal k of the sub O ₂ sensor 16 except during execution of the air-fuel ratio control program described below.

In the air-fuel ratio control program, the air-fuel ratio correction constant set based on the output of the main O ₂ sensor 15 after detecting the activation of the main O ₂ sensor 15 that is an oxygen sensor is used. Controls the air-fuel ratio, and records that the fuel supply has been stopped after detecting that the main O ₂ sensor 15 is activated as a fuel cut history, and if there is no record of the fuel cut history, the fuel cut A predetermined air-fuel ratio correction constant is selected so that the air-fuel ratio becomes leaner than when there is a history record.

  The air-fuel ratio control program of this embodiment will be described with reference to FIG. This air-fuel ratio control program is executed when the engine 100 is in a cold state from when the main oxygen sensor 15 is fully activated until the warm-up is completed after the engine 100 is started in the cold state. Is.

First, in step S1, it is determined whether or not the main O ₂ sensor 15 is sufficiently activated. Activation of the main O ₂ sensor 15 is determined based on the state of the output signal h. When the main O ₂ sensor 15 is activated, a more agile reaction is exhibited than when the output signal h is not activated. Specifically, for example, the activation of the main O ₂ sensor 15 is determined based on the rising or falling slope (speed) of the output signal h. Since the main O ₂ sensor 15 shows a slightly slower reaction than the case where the main O ₂ sensor 15 is completely activated even during a predetermined time immediately after the activation determination, the main O ₂ sensor 15 Is fully activated after a predetermined time.

If it is determined in step S1 that the main O ₂ sensor 15 has been activated, whether or not a fuel cut history indicating that a fuel cut, which is a control for stopping the supply of fuel, that is, the injection, has been performed is recorded in step S2. Determine whether. That is, the fuel cut history is recorded when the fuel cut is executed after the engine is started until the engine 100 is warmed up, and the fuel cut history is not recorded when the fuel cut is not executed.

  In step S3, it is determined that the fuel cut history is not recorded, that is, the fuel supply is not stopped, and the air-fuel ratio correction constant is selected so that the air-fuel ratio becomes lean. In this case, specifically, selection is made so that the delay time TDL as the air-fuel ratio correction constant becomes longer. By this selection of the delay time TDL, the time until the air-fuel ratio is switched to the rich side is lengthened, and the air-fuel ratio becomes lean accordingly. Generally, before the warm-up operation is completed, the air-fuel ratio is controlled to be richer in order to ensure drivability. Accordingly, in such an embodiment, since the oxygen in the three-way catalyst 14 tends to be insufficient, the delay time TDL is selected to be on the lean side.

  In step S4, since it is determined that the fuel cut history is recorded, the delay time TDL is selected to be substantially stoichiometric or slightly lean. Thereafter, in step S5, it is determined whether or not the warm-up operation is completed. If not, the process returns to step S2.

In such a configuration, the case where the engine 100 is started and the main O ₂ sensor 15 is sufficiently activated and then the automobile is stopped, that is, the engine 100 is in the idle operation state will be described. . As described above, when the supply of fuel is not stopped until the engine 100 is in the idle operation state and the warm-up operation is completed, the fuel cut history is not recorded. During this time, since the air-fuel ratio is set slightly richer than the stoichiometric ratio, the oxygen in the three-way catalyst 14 decreases due to the oxidation reaction with CO and HC.

  Therefore, Step S1, Step S2, and Step S3 are executed in this order to select the air-fuel ratio correction constant so that the air-fuel ratio is stoichiometric or slightly lean. Thereby, the inside of the three way catalyst 14 will be in the state which oxygen increases. In this way, when the oxygen in the three-way catalyst 14 increases, the oxidation reaction is promoted and the temperature of the three-way catalyst 14 rises. As the temperature rises, the activation of the three-way catalyst 14 can be accelerated even in the engine 100 in the idle operation state. Therefore, the purification efficiency of the three-way catalyst 14 before activation can be improved, and NOx, CO, and HC can be suppressed from being discharged when the automobile starts.

On the other hand, after the main O ₂ sensor 15 is fully activated, until the warm-up operation is completed, that is, when the engine 100 is in the cold state, the vehicle is driven and the fuel supply is stopped by deceleration or the like. When a situation occurs, a large amount of air flows into the three-way catalyst 14 during that time by not supplying fuel. For this reason, the oxygen-deficient state due to the start-up or the operation in the cold state is eliminated, and it becomes possible to keep it slightly in the vicinity of the stoichiometric lean side. In this way, the oxygen in the three-way catalyst 14 increases, the oxidation reaction is promoted, and the activation of the three-way catalyst 14 is promoted.

  In this way, while the vehicle is stopped, the delay time TDL is selected so that the air-fuel ratio becomes lean, and when the vehicle is cut once and fuel cut is performed, the delay is made so that the air-fuel ratio becomes slightly lean or stoichiometric. By selecting the time TDL, it is possible to improve the purification capacity of the three-way catalyst 14 until the engine 100 reaches the state where the warm-up operation is completed.

  In addition, this invention is not limited to the above-mentioned embodiment.

  In the above-described embodiment, the delay times TDR and TDL as the air-fuel ratio correction constant have been described. However, skip values RSP and RSM for controlling the feedback correction coefficient FAF, or integration constants KIM and KIP may be used. In this case, the skip value RSP is selected (adjusted) to reduce the value, the skip value RSM is selected to increase the value, the integration constant KIP decreases the rate of change, and the integration constant KIM increases the rate of change. Choose to do. As described above, by selecting the skip value RSP, RSM or the integral constants KIM, KIP of the feedback correction coefficient FAF, the variable range, that is, the amplitude of the feedback correction coefficient FAF is reduced, and the same effect as the above-described embodiment can be obtained. It is.

In the above description, the engine in which the O ₂ sensors are arranged before and after the catalyst has been described. However, the engine may be applied to an engine having only the main O ₂ sensor 15 in the above-described embodiment.

In addition, the activation determination of the main O ₂ sensor 15 may be performed based on the elapsed time from the start of the engine 100.

  In addition, the specific configuration of each part is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention.

1 is a schematic configuration diagram of an embodiment of the present invention. 3 is a timing chart showing the basic air-fuel ratio control operation of the embodiment. The flowchart which shows the control procedure of the embodiment.

Explanation of symbols

6 ... electronic controller 14 ... three-way catalyst 15 ... main O ₂ sensor 16 ... sub O ₂ sensor 17 ... central processing unit 18 ... memory 19 ... input interface 20 ... Output Interface

Claims (1)

In an internal combustion engine including a catalyst provided in the exhaust passage and an oxygen sensor provided upstream of the catalyst, an air-fuel ratio correction constant set based on the output of the oxygen sensor after detecting that the oxygen sensor is activated An air-fuel ratio control method for an internal combustion engine that uses an air-fuel ratio to control,
Record that the fuel supply was stopped after detecting the activation of the oxygen sensor as a fuel cut history,
An air-fuel ratio control method for an internal combustion engine that selects a predetermined air-fuel ratio correction constant so that the air-fuel ratio becomes leaner than when there is no fuel cut history record when there is no fuel cut history record.

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