JP2014218946A - Air fuel ratio control device for internal combustion engine - Google Patents

Air fuel ratio control device for internal combustion engine Download PDF

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JP2014218946A
JP2014218946A JP2013099090A JP2013099090A JP2014218946A JP 2014218946 A JP2014218946 A JP 2014218946A JP 2013099090 A JP2013099090 A JP 2013099090A JP 2013099090 A JP2013099090 A JP 2013099090A JP 2014218946 A JP2014218946 A JP 2014218946A
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fuel ratio
air
output characteristic
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control
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雅徳 黒澤
Masanori Kurosawa
雅徳 黒澤
小栗　隆雅
Takamasa Oguri
小栗　　隆雅
小池　聡
Satoshi Koike
聡 小池
松岡幹泰
Mikiyasu Matsuoka
幹泰 松岡
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Denso Corp
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Denso Corp
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Priority to PCT/JP2014/002273 priority patent/WO2014181512A1/en
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/0025—Controlling engines characterised by use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures
    • F02D41/0047—Controlling exhaust gas recirculation [EGR]
    • F02D41/005—Controlling exhaust gas recirculation [EGR] according to engine operating conditions
    • F02D41/0052—Feedback control of engine parameters, e.g. for control of air/fuel ratio or intake air amount
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D21/00—Controlling engines characterised by their being supplied with non-airborne oxygen or other non-fuel gas
    • F02D21/06—Controlling engines characterised by their being supplied with non-airborne oxygen or other non-fuel gas peculiar to engines having other non-fuel gas added to combustion air
    • F02D21/08—Controlling engines characterised by their being supplied with non-airborne oxygen or other non-fuel gas peculiar to engines having other non-fuel gas added to combustion air the other gas being the exhaust gas of engine
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/02—Circuit arrangements for generating control signals
    • F02D41/04—Introducing corrections for particular operating conditions
    • F02D41/06—Introducing corrections for particular operating conditions for engine starting or warming up
    • F02D41/068—Introducing corrections for particular operating conditions for engine starting or warming up for warming-up
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/02—Circuit arrangements for generating control signals
    • F02D41/14—Introducing closed-loop corrections
    • F02D41/1438—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor
    • F02D41/1439—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the position of the sensor
    • F02D41/1441—Plural sensors
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/02—Circuit arrangements for generating control signals
    • F02D41/14—Introducing closed-loop corrections
    • F02D41/1438—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor
    • F02D41/1444—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases
    • F02D41/1454—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases the characteristics being an oxygen content or concentration or the air-fuel ratio
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/02—Circuit arrangements for generating control signals
    • F02D41/14—Introducing closed-loop corrections
    • F02D41/1438—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor
    • F02D41/1444—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases
    • F02D41/1454—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases the characteristics being an oxygen content or concentration or the air-fuel ratio
    • F02D41/1458—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases the characteristics being an oxygen content or concentration or the air-fuel ratio with determination means using an estimation
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/02—Circuit arrangements for generating control signals
    • F02D41/14—Introducing closed-loop corrections
    • F02D41/1438—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor
    • F02D41/1493—Details
    • F02D41/1494—Control of sensor heater
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/0004—Gaseous mixtures, e.g. polluted air
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2560/00—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics
    • F01N2560/02—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics the means being an exhaust gas sensor
    • F01N2560/025—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics the means being an exhaust gas sensor for measuring or detecting O2, e.g. lambda sensors
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2560/00—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics
    • F01N2560/14—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics having more than one sensor of one kind
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/40—Engine management systems

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  • Combined Controls Of Internal Combustion Engines (AREA)
  • Electrical Control Of Air Or Fuel Supplied To Internal-Combustion Engine (AREA)
  • Exhaust Gas After Treatment (AREA)
  • Output Control And Ontrol Of Special Type Engine (AREA)

Abstract

PROBLEM TO BE SOLVED: To expand a control region of an air fuel ratio of catalyst inflow gas while reducing a control amplitude of an air fuel ratio F/B (feedback) control on the basis of output from an upstream side oxygen sensor.SOLUTION: An air fuel ratio control device for an internal combustion engine includes a constant current circuit for changing output characteristics of an upstream side oxygen sensor 25 by making a constant current flow between sensor electrodes of the upstream side oxygen sensor 25. When output from a downstream side oxygen sensor 26 is on the rich side of target voltage, the output characteristics of the upstream side oxygen sensor 25 are switched to the lean direction. Thus, a control center of air fuel ratio F/B control on the basis of the output from the upstream side oxygen sensor 25 is changed to the lean direction and a control region of an air fuel ratio of catalyst inflow gas is expanded in the lean direction. In contrast, when the output from the downstream side oxygen sensor 26 is on the lean side of the target voltage, the output characteristics of the upstream side oxygen sensor 25 are switched to the rich direction. Thus, the control center of the air fuel ratio F/B control is changed to the rich direction and the control region of the air fuel ratio of the catalyst inflow gas is expanded in the rich direction.

Description

本発明は、内燃機関の排出ガス浄化用の触媒の上流側の排出ガスのリッチ／リーンを検出する上流側センサの出力に基づいて空燃比フィードバック制御を行う内燃機関の空燃比制御装置に関する発明である。   The present invention relates to an air-fuel ratio control apparatus for an internal combustion engine that performs air-fuel ratio feedback control based on an output of an upstream sensor that detects rich / lean exhaust gas upstream of a catalyst for purifying exhaust gas of the internal combustion engine. is there.

近年、内燃機関を搭載した車両では、排気管に排出ガス浄化用の触媒を設置すると共に、この触媒の上流側や下流側に排出ガスの空燃比又はリッチ／リーンを検出する排出ガスセンサ（空燃比センサ又は酸素センサ）を設置し、排出ガスセンサの出力に基づいて空燃比をＦ／Ｂ（フィードバック）制御して触媒の排出ガス浄化率を高めるようにしたものがある。   In recent years, in vehicles equipped with an internal combustion engine, a catalyst for purifying exhaust gas is installed in an exhaust pipe, and an exhaust gas sensor (air-fuel ratio) that detects an air-fuel ratio or rich / lean of exhaust gas upstream or downstream of the catalyst. Some sensors or oxygen sensors are installed, and the exhaust gas purification rate of the catalyst is increased by F / B (feedback) control of the air-fuel ratio based on the output of the exhaust gas sensor.

このような空燃比制御システムにおいては、例えば、特許文献１（特許第３８７６６４２号公報）に記載されているように、触媒の上流側の酸素センサの出力に基づいた空燃比Ｆ／Ｂ制御のＰＩＤ制御量を逐次算出することで、空燃比Ｆ／Ｂ制御の制御振幅の低振幅化と制御周波数の高周波数化を両立して、触媒の排出ガス浄化率を向上させるようにしたものがある。   In such an air-fuel ratio control system, for example, as described in Patent Document 1 (Japanese Patent No. 3876642), a PID for air-fuel ratio F / B control based on the output of an oxygen sensor upstream of the catalyst is used. There is one that improves the exhaust gas purification rate of the catalyst by simultaneously calculating the control amount so as to achieve both the reduction of the control amplitude of the air-fuel ratio F / B control and the increase of the control frequency.

特許第３８７６６４２号公報Japanese Patent No. 3876642

近年の排出ガス浄化率の更なる向上の要求に伴う触媒性能（酸素吸蔵能力等）の向上により、触媒流出ガス（触媒の下流側の排出ガス）の目標空燃比を理論空燃比よりもリッチ側に設定することもある。しかし、上流側の酸素センサの出力に基づいた空燃比Ｆ／Ｂ制御では、触媒流入ガス（触媒の上流側の排出ガス）の空燃比を、酸素センサの出力のリッチ／リーンが反転する空燃比（例えば理論空燃比付近）を中心に制御するため、空燃比Ｆ／Ｂ制御の制御振幅を低振幅化すると、触媒流入ガスの空燃比の制御変化幅が小さくなって、触媒流入ガスの空燃比の制御領域が狭くなる。触媒流入ガスの空燃比の制御領域が狭くなると、触媒流出ガスの空燃比の制御領域も狭くなり、触媒流出ガスの空燃比を目標空燃比に制御することが困難になる。   The target air-fuel ratio of the catalyst outflow gas (exhaust gas on the downstream side of the catalyst) is made richer than the stoichiometric air-fuel ratio due to improvements in catalyst performance (oxygen storage capacity, etc.) in response to the demand for further improvement in exhaust gas purification rate in recent years. It may be set to. However, in the air-fuel ratio F / B control based on the output of the upstream oxygen sensor, the air-fuel ratio of the catalyst inflow gas (exhaust gas upstream of the catalyst) is reversed by the rich / lean output of the oxygen sensor. If the control amplitude of the air-fuel ratio F / B control is reduced to reduce the control amplitude mainly in the vicinity of the theoretical air-fuel ratio (for example, the vicinity of the theoretical air-fuel ratio), the control change width of the air-fuel ratio of the catalyst inflow gas becomes small, and The control area becomes narrower. If the control range of the air-fuel ratio of the catalyst inflow gas is narrowed, the control range of the air-fuel ratio of the catalyst outflow gas is also narrowed, and it becomes difficult to control the air-fuel ratio of the catalyst outflow gas to the target air-fuel ratio.

そこで、本発明が解決しようとする課題は、上流側センサの出力に基づいた空燃比フィードバック制御の制御振幅を低振幅化しながら触媒流入ガスの空燃比の制御領域を拡大することができる内燃機関の空燃比制御装置を提供することにある。   Accordingly, the problem to be solved by the present invention is that of an internal combustion engine capable of expanding the control range of the air-fuel ratio of the catalyst inflow gas while reducing the control amplitude of the air-fuel ratio feedback control based on the output of the upstream sensor. An object is to provide an air-fuel ratio control device.

上記課題を解決するために、請求項１に係る発明は、内燃機関（１１）の排出ガスを浄化する触媒（２４）と、この触媒（２４）の上流側の排出ガスの空燃比のリッチ／リーンを検出する上流側センサ（２５）と、触媒（２４）の下流側の排出ガスの空燃比を検出又は推定する下流側空燃比取得手段（２６）とを備え、上流側センサ（２５）の出力に基づいて空燃比フィードバック制御を行う内燃機関の空燃比制御装置において、上流側センサ（２５）の出力特性を変更する出力特性変更手段（４８）と、下流側空燃比取得手段（２６）の出力に応じて上流側センサ（２５）の出力特性を変更するように出力特性変更手段（４８）を制御する出力特性変更制御手段（３８）とを備えた構成としたものである。   In order to solve the above-mentioned problem, the invention according to claim 1 is directed to a catalyst (24) for purifying exhaust gas of the internal combustion engine (11), and a rich air / fuel ratio of exhaust gas upstream of the catalyst (24). An upstream sensor (25) for detecting lean, and a downstream air-fuel ratio acquisition means (26) for detecting or estimating the air-fuel ratio of the exhaust gas downstream of the catalyst (24), and the upstream sensor (25) In an air-fuel ratio control apparatus for an internal combustion engine that performs air-fuel ratio feedback control based on the output, an output characteristic changing means (48) for changing the output characteristics of the upstream sensor (25), and a downstream air-fuel ratio acquisition means (26) An output characteristic change control means (38) for controlling the output characteristic change means (48) so as to change the output characteristic of the upstream sensor (25) according to the output is provided.

上流側センサの出力に基づいた空燃比Ｆ／Ｂ（フィードバック）制御の制御振幅を低振幅化すると、触媒流入ガス（触媒の上流側の排出ガス）の空燃比の制御変化幅が小さくなるが、本発明は、下流側空燃比取得手段の出力に応じて上流側センサの出力特性を変更することで、上流側センサの出力に基づいた空燃比Ｆ／Ｂ制御の制御中心（上流側センサの出力のリッチ／リーンが反転する空燃比）を変更して、触媒流入ガスの空燃比の制御領域を拡大することができる。これにより、上流側センサの出力に基づいた空燃比Ｆ／Ｂ制御の制御振幅を低振幅化しながら触媒流入ガスの空燃比の制御領域を拡大することができる。その結果、触媒流出ガス（触媒の下流側の排出ガス）の空燃比の制御領域も拡大することができ、触媒流出ガスの空燃比を目標空燃比に制御することが可能となる。   When the control amplitude of the air-fuel ratio F / B (feedback) control based on the output of the upstream side sensor is lowered, the control change width of the air-fuel ratio of the catalyst inflow gas (exhaust gas upstream of the catalyst) is reduced. The present invention changes the output characteristics of the upstream sensor in accordance with the output of the downstream air-fuel ratio acquisition means, thereby controlling the control center of the air-fuel ratio F / B control based on the output of the upstream sensor (the output of the upstream sensor). It is possible to expand the control range of the air-fuel ratio of the catalyst inflow gas by changing the rich / lean air-fuel ratio. As a result, the control range of the air-fuel ratio of the catalyst inflow gas can be expanded while reducing the control amplitude of the air-fuel ratio F / B control based on the output of the upstream sensor. As a result, the control range of the air / fuel ratio of the catalyst outflow gas (exhaust gas on the downstream side of the catalyst) can be expanded, and the air / fuel ratio of the catalyst outflow gas can be controlled to the target air / fuel ratio.

図１は本発明の一実施例におけるエンジン制御システムの概略構成を示す図である。FIG. 1 is a diagram showing a schematic configuration of an engine control system in one embodiment of the present invention. 図２はセンサ素子の構成を示す断面図である。FIG. 2 is a cross-sectional view showing the configuration of the sensor element. 図３は酸素センサの出力特性を示す図である。FIG. 3 is a diagram showing output characteristics of the oxygen sensor. 図４は下流側酸素センサ出力に応じた出力特性変更制御の実行例を示すタイムチャートである。FIG. 4 is a time chart showing an execution example of the output characteristic change control according to the downstream oxygen sensor output. 図５は外部ＥＧＲ量に応じた出力特性変更制御の実行例を示すタイムチャートである。FIG. 5 is a time chart showing an execution example of output characteristic change control according to the external EGR amount. 図６はバルブタイミング制御量に応じた出力特性変更制御の実行例を示すタイムチャートである。FIG. 6 is a time chart showing an execution example of the output characteristic change control according to the valve timing control amount. 図７は出力特性変更制御メインルーチンの処理の流れを示すローチャートである。FIG. 7 is a flowchart showing the flow of processing of the output characteristic change control main routine. 図８は出力特性変更制御ルーチンの処理の流れを示すローチャートである。FIG. 8 is a flowchart showing the processing flow of the output characteristic change control routine. 図９は触媒暖機制御ルーチンの処理の流れを示すフローチャートである。FIG. 9 is a flowchart showing a process flow of the catalyst warm-up control routine.

以下、本発明を実施するための形態を具体化した一実施例を説明する。
まず、図１に基づいてエンジン制御システムの概略構成を説明する。
内燃機関であるエンジン１１の吸気管１２の最上流部には、エアクリーナ１３が設けられ、このエアクリーナ１３の下流側に、吸入空気量を検出するエアフローメータ１４が設けられている。このエアフローメータ１４の下流側には、モータ１５によって開度調節されるスロットルバルブ１６と、このスロットルバルブ１６の開度（スロットル開度）を検出するスロットル開度センサ１７とが設けられている。 Hereinafter, an embodiment embodying a mode for carrying out the present invention will be described.
First, a schematic configuration of the engine control system will be described with reference to FIG.
An air cleaner 13 is provided at the most upstream portion of the intake pipe 12 of the engine 11 that is an internal combustion engine, and an air flow meter 14 that detects the intake air amount is provided downstream of the air cleaner 13. A throttle valve 16 whose opening is adjusted by a motor 15 and a throttle opening sensor 17 for detecting the opening (throttle opening) of the throttle valve 16 are provided on the downstream side of the air flow meter 14.

更に、スロットルバルブ１６の下流側には、サージタンク１８が設けられ、このサージタンク１８に、吸気管圧力を検出する吸気管圧力センサ１９が設けられている。また、サージタンク１８には、エンジン１１の各気筒に空気を導入する吸気マニホールド２０が設けられ、各気筒の吸気マニホールド２０に接続された吸気ポート又はその近傍に、それぞれ吸気ポートに燃料を噴射する燃料噴射弁２１が取り付けられている。また、エンジン１１のシリンダヘッドには、各気筒毎に点火プラグ２２が取り付けられ、各気筒の点火プラグ２２の火花放電によって各気筒内の混合気に着火される。   Further, a surge tank 18 is provided on the downstream side of the throttle valve 16, and an intake pipe pressure sensor 19 for detecting the intake pipe pressure is provided in the surge tank 18. In addition, the surge tank 18 is provided with an intake manifold 20 for introducing air into each cylinder of the engine 11, and fuel is injected into the intake port at or near the intake port connected to the intake manifold 20 of each cylinder. A fuel injection valve 21 is attached. An ignition plug 22 is attached to the cylinder head of the engine 11 for each cylinder, and the air-fuel mixture in each cylinder is ignited by spark discharge of the ignition plug 22 of each cylinder.

一方、エンジン１１の排気管２３には、排出ガス中のＣＯ、ＨＣ、ＮＯX 等を浄化する三元触媒等の触媒２４が設けられている。この触媒２４の上流側には、触媒流入ガス（触媒２４の上流側の排出ガス）の空燃比のリッチ／リーンを検出する上流側酸素センサ２５（上流側センサ）が設けられ、触媒２４の下流側には、触媒流出ガス（触媒２４の下流側の排出ガス）の空燃比のリッチ／リーンを検出する下流側酸素センサ２６（下流側空燃比取得手段）が設けられている。 On the other hand, the exhaust pipe 23 of the engine 11 is provided with a catalyst 24 such as a three-way catalyst for purifying CO, HC, NO x and the like in the exhaust gas. An upstream oxygen sensor 25 (upstream sensor) for detecting the rich / lean of the air-fuel ratio of the catalyst inflow gas (the exhaust gas upstream of the catalyst 24) is provided on the upstream side of the catalyst 24. On the side, a downstream oxygen sensor 26 (downstream air-fuel ratio acquisition means) that detects rich / lean air-fuel ratio of the catalyst outflow gas (exhaust gas downstream of the catalyst 24) is provided.

また、エンジン１１には、吸気バルブ２７のバルブタイミング（開閉タイミング）を変化させる吸気側可変バルブタイミング装置２９と、排気バルブ２８のバルブタイミングを変化させる排気側可変バルブタイミング装置３０とが設けられている。   Further, the engine 11 is provided with an intake side variable valve timing device 29 that changes the valve timing (opening / closing timing) of the intake valve 27 and an exhaust side variable valve timing device 30 that changes the valve timing of the exhaust valve 28. Yes.

更に、エンジン１１には、排出ガスの一部をＥＧＲガスとして吸気側へ還流させるＥＧＲ装置３１が搭載されている。このＥＧＲ装置３１は、排気管２３のうちの触媒２４の上流側と吸気管１２のうちのスロットルバルブ１６の下流側（又はサージタンク１８）との間にＥＧＲ配管３２が接続され、このＥＧＲ配管３２にＥＧＲガス流量（外部ＥＧＲ量）を調整するＥＧＲ弁３３が設けられている。   Further, the engine 11 is equipped with an EGR device 31 that recirculates a part of the exhaust gas to the intake side as EGR gas. The EGR device 31 has an EGR pipe 32 connected between the upstream side of the catalyst 24 in the exhaust pipe 23 and the downstream side (or the surge tank 18) of the throttle valve 16 in the intake pipe 12. 32 is provided with an EGR valve 33 that adjusts the EGR gas flow rate (external EGR amount).

また、エンジン１１のシリンダブロックには、冷却水温を検出する冷却水温センサ３４や、ノッキングを検出するノックセンサ３５が取り付けられている。また、クランク軸３６の外周側には、クランク軸３６が所定クランク角回転する毎にパルス信号を出力するクランク角センサ３７が取り付けられ、このクランク角センサ３７の出力信号に基づいてクランク角やエンジン回転速度が検出される。   A cooling water temperature sensor 34 that detects the cooling water temperature and a knock sensor 35 that detects knocking are attached to the cylinder block of the engine 11. A crank angle sensor 37 that outputs a pulse signal every time the crankshaft 36 rotates by a predetermined crank angle is attached to the outer peripheral side of the crankshaft 36. Based on the output signal of the crank angle sensor 37, the crank angle and engine The rotation speed is detected.

これら各種センサの出力は、電子制御ユニット（以下「ＥＣＵ」と表記する）３８に入力される。このＥＣＵ３８は、マイクロコンピュータを主体として構成され、内蔵されたＲＯＭ（記憶媒体）に記憶された各種のエンジン制御用のプログラムを実行することで、エンジン運転状態に応じて、燃料噴射量、点火時期、スロットル開度（吸入空気量）等を制御する。   Outputs of these various sensors are input to an electronic control unit (hereinafter referred to as “ECU”) 38. The ECU 38 is mainly composed of a microcomputer, and executes various engine control programs stored in a built-in ROM (storage medium), so that the fuel injection amount and the ignition timing are determined according to the engine operating state. The throttle opening (intake air amount) and the like are controlled.

その際、ＥＣＵ３８は、所定の空燃比Ｆ／Ｂ制御実行条件が成立したときに、上流側酸素センサ２５の出力に基づいて触媒流入ガスの空燃比を上流側目標空燃比（例えば理論空燃比）付近に制御するようにＰＩＤ制御等により燃料噴射量をＦ／Ｂ補正する空燃比Ｆ／Ｂ制御を実行する。ここで、「Ｆ／Ｂ」は「フィードバック」を意味する（以下、同様）。更に、所定のサブＦ／Ｂ制御実行条件が成立したときに、下流側酸素センサ２６の出力に基づいて触媒流出ガスの空燃比を下流側目標空燃比付近に制御するように空燃比Ｆ／Ｂ制御を修正するサブＦ／Ｂ制御を実行する。このサブＦ／Ｂ制御では、例えば、空燃比Ｆ／Ｂ制御の制御中心（上流側目標空燃比）又はＦ／Ｂ補正量等を修正する。   At this time, the ECU 38 sets the air-fuel ratio of the catalyst inflow gas to the upstream target air-fuel ratio (for example, the theoretical air-fuel ratio) based on the output of the upstream oxygen sensor 25 when a predetermined air-fuel ratio F / B control execution condition is satisfied. Air-fuel ratio F / B control is performed to correct the fuel injection amount by F / B by PID control or the like so as to control the vicinity. Here, “F / B” means “feedback” (hereinafter the same). Further, when a predetermined sub F / B control execution condition is established, the air-fuel ratio F / B is controlled so that the air-fuel ratio of the catalyst outflow gas is controlled in the vicinity of the downstream target air-fuel ratio based on the output of the downstream oxygen sensor 26. The sub F / B control for correcting the control is executed. In this sub F / B control, for example, the control center (upstream target air-fuel ratio) of the air-fuel ratio F / B control or the F / B correction amount is corrected.

次に、図２に基づいて上流側酸素センサ２５の構成を説明する。尚、下流側酸素センサ２６の構成は上流側酸素センサ２５の構成と実質的に同一である。
上流側酸素センサ２５は、コップ型構造のセンサ素子４１を有しており、実際には当該センサ素子４１は素子全体が図示しないハウジングや素子カバー内に収容される構成となっており、エンジン１１の排気管２３内に配設されている。 Next, the configuration of the upstream oxygen sensor 25 will be described with reference to FIG. The configuration of the downstream oxygen sensor 26 is substantially the same as the configuration of the upstream oxygen sensor 25.
The upstream oxygen sensor 25 has a cup-shaped sensor element 41. Actually, the sensor element 41 is configured to be housed in a housing or an element cover (not shown), and the engine 11 Is disposed in the exhaust pipe 23.

センサ素子４１において、固体電解質層４２（固体電解質体）は、断面コップ状に形成されており、その外表面には排気側電極層４３が設けられ、内表面には大気側電極層４４が設けられている。固体電解質層４２は、ＺｒＯ2 、ＨｆＯ2 、ＴｈＯ2 、Ｂｉ2 Ｏ3 等にＣａＯ、ＭｇＯ、Ｙ2 Ｏ3 、Ｙｂ2 Ｏ3 等を安定剤として固溶させた酸素イオン伝導性酸化物焼結体からなる。また、各電極層４３，４４は共に白金等の触媒活性の高い貴金属からなり、その表面には多孔質の化学メッキ等が施されている。これらの電極層４３，４４が一対の対向電極（センサ電極）となっている。固体電解質層４２にて囲まれる内部空間は大気室４５となっており、その大気室４５内にはヒータ４６が収容されている。このヒータ４６は、センサ素子４１を活性化するのに十分な発熱容量を有しており、その発熱エネルギによりセンサ素子４１全体が加熱される。センサ素子４１の活性温度は、例えば３５０〜４００℃程度である。尚、大気室４５は、大気が導入されることでその内部が所定酸素濃度に保持され、大気側電極層４４が大気室４５内の大気に晒されている。 In the sensor element 41, the solid electrolyte layer 42 (solid electrolyte body) is formed in a cup shape in cross section, an exhaust side electrode layer 43 is provided on the outer surface, and an air side electrode layer 44 is provided on the inner surface. It has been. The solid electrolyte layer 42 is an oxygen ion conductive oxide-fired oxide in which CaO, MgO, Y 2 O 3 , Yb 2 O 3 or the like is dissolved in ZrO 2 , HfO 2 , ThO 2 , Bi 2 O 3 or the like as a stabilizer. Consists of union. Each of the electrode layers 43 and 44 is made of a noble metal having high catalytic activity such as platinum, and the surface thereof is subjected to porous chemical plating or the like. These electrode layers 43 and 44 form a pair of counter electrodes (sensor electrodes). An internal space surrounded by the solid electrolyte layer 42 is an atmospheric chamber 45, and a heater 46 is accommodated in the atmospheric chamber 45. The heater 46 has a heat generation capacity sufficient to activate the sensor element 41, and the entire sensor element 41 is heated by the heat generation energy. The activation temperature of the sensor element 41 is, for example, about 350 to 400 ° C. The atmosphere chamber 45 is maintained at a predetermined oxygen concentration by introducing the atmosphere, and the atmosphere-side electrode layer 44 is exposed to the atmosphere in the atmosphere chamber 45.

センサ素子４１では、固体電解質層４２の外側（電極層４３側）が排気雰囲気、固体電解質層４２の内側（電極層４４側）が大気雰囲気となっており、これら双方の酸素濃度の差（酸素分圧の差）に応じて電極層４３，４４間で起電力が発生する。つまり、センサ素子４１では、空燃比がリッチかリーンかで異なる起電力が発生する。これにより、センサ素子４１は、排出ガスの酸素濃度（すなわち空燃比）に応じた起電力信号を出力する。   In the sensor element 41, the outside of the solid electrolyte layer 42 (on the electrode layer 43 side) is an exhaust atmosphere, and the inside of the solid electrolyte layer 42 (on the electrode layer 44 side) is an air atmosphere. An electromotive force is generated between the electrode layers 43 and 44 in accordance with the difference in partial pressure. That is, the sensor element 41 generates different electromotive forces depending on whether the air-fuel ratio is rich or lean. Thereby, the sensor element 41 outputs an electromotive force signal corresponding to the oxygen concentration (that is, the air-fuel ratio) of the exhaust gas.

センサ素子４１は、空燃比が理論空燃比（空気過剰率λ＝１）に対してリッチかリーンかで異なる起電力を発生し、理論空燃比（空気過剰率λ＝１）付近で起電力が急変する特性を有する（図３の実線参照）。具体的には、空燃比がリッチ時のセンサ起電力は約０．９Ｖであり、空燃比がリーン時のセンサ起電力は約０Ｖである。   The sensor element 41 generates an electromotive force that differs depending on whether the air-fuel ratio is rich or lean with respect to the stoichiometric air-fuel ratio (excess air ratio λ = 1), and the electromotive force near the stoichiometric air-fuel ratio (excess air ratio λ = 1). It has characteristics that change suddenly (see the solid line in FIG. 3). Specifically, the sensor electromotive force when the air-fuel ratio is rich is about 0.9 V, and the sensor electromotive force when the air-fuel ratio is lean is about 0 V.

図２に示すように、センサ素子４１の排気側電極層４３は接地され、大気側電極層４４にはマイコン４７が接続されている。排出ガスの空燃比（酸素濃度）に応じてセンサ素子４１にて起電力が発生すると、その起電力に相当するセンサ検出信号がマイコン４７に対して出力される。マイコン４７は、例えばＥＣＵ３８内に設けられており、センサ検出信号に基づいて空燃比を算出する。   As shown in FIG. 2, the exhaust electrode layer 43 of the sensor element 41 is grounded, and the microcomputer 47 is connected to the atmosphere electrode layer 44. When an electromotive force is generated in the sensor element 41 in accordance with the air-fuel ratio (oxygen concentration) of the exhaust gas, a sensor detection signal corresponding to the electromotive force is output to the microcomputer 47. The microcomputer 47 is provided in the ECU 38, for example, and calculates the air-fuel ratio based on the sensor detection signal.

また、本実施例では、上流側酸素センサ２５の大気側電極層４４に定電流回路４８（出力特性変更手段）が接続され、この定電流回路４８による定電流Ｉｃｓの供給をＥＣＵ３８（マイコン４７）により制御して、上流側酸素センサ２５の一対のセンサ電極４３，４４間（排気側電極層４３と大気側電極層４４との間）に定電流を流すことで、上流側酸素センサ２５の出力特性を変更するようにしている。   In this embodiment, a constant current circuit 48 (output characteristic changing means) is connected to the atmosphere side electrode layer 44 of the upstream oxygen sensor 25, and the constant current Ics is supplied by the constant current circuit 48 to the ECU 38 (microcomputer 47). The output of the upstream oxygen sensor 25 is controlled by flowing a constant current between the pair of sensor electrodes 43 and 44 of the upstream oxygen sensor 25 (between the exhaust electrode layer 43 and the atmosphere electrode layer 44). The characteristics are changed.

本実施例では、大気側電極層４４→排気側電極層４３の向きに流れる定電流Ｉｃｓを正の定電流とし、排気側電極層４３→大気側電極層４４の向きに流れる定電流Ｉｃｓを負の定電流としている。図３に示すように、上流側酸素センサ２５のセンサ電極４３，４４間に正の定電流を流すと、上流側酸素センサ２５の出力特性がリーン方向にシフトする（上流側酸素センサ２５の出力のリッチ／リーンが反転する変曲点がリーン方向にシフトする）ようになっている。一方、上流側酸素センサ２５のセンサ電極４３，４４間に負の定電流を流すと、上流側酸素センサ２５の出力特性がリッチ方向にシフトする（上流側酸素センサ２５の出力のリッチ／リーンが反転する変曲点がリッチ方向にシフトする）ようになっている。   In this embodiment, the constant current Ics flowing in the direction from the atmosphere side electrode layer 44 to the exhaust side electrode layer 43 is set as a positive constant current, and the constant current Ics flowing in the direction from the exhaust side electrode layer 43 to the atmosphere side electrode layer 44 is negative. Constant current. As shown in FIG. 3, when a positive constant current is passed between the sensor electrodes 43 and 44 of the upstream oxygen sensor 25, the output characteristics of the upstream oxygen sensor 25 shift in the lean direction (the output of the upstream oxygen sensor 25). The inflection point at which the rich / lean reversal shifts in the lean direction). On the other hand, when a negative constant current is passed between the sensor electrodes 43 and 44 of the upstream oxygen sensor 25, the output characteristics of the upstream oxygen sensor 25 shift in the rich direction (the rich / lean output of the upstream oxygen sensor 25 is reduced). The inflection point to be inverted shifts in the rich direction).

近年の排出ガス浄化率の更なる向上の要求に伴う触媒性能（酸素吸蔵能力等）の向上により、下流側目標空燃比（触媒流出ガスの目標空燃比）を理論空燃比よりもリッチ側に設定することもある。しかし、上流側酸素センサ２５の出力に基づいた空燃比Ｆ／Ｂ制御では、触媒流入ガスの空燃比を、上流側酸素センサ２５の出力のリッチ／リーンが反転する空燃比（例えば理論空燃比付近）を中心に制御するため、空燃比Ｆ／Ｂ制御の制御振幅を低振幅化すると、触媒流入ガスの空燃比の制御変化幅が小さくなって、触媒流入ガスの空燃比の制御領域が狭くなる。触媒流入ガスの空燃比の制御領域が狭くなると、触媒流出ガスの空燃比の制御領域も狭くなり、触媒流出ガスの空燃比を下流側目標空燃比に制御することが困難になる。   The downstream target air-fuel ratio (target air-fuel ratio of catalyst outflow gas) is set to be richer than the stoichiometric air-fuel ratio by improving the catalyst performance (oxygen storage capacity, etc.) in response to the demand for further improvement in exhaust gas purification rate in recent years. Sometimes. However, in the air-fuel ratio F / B control based on the output of the upstream oxygen sensor 25, the air-fuel ratio of the catalyst inflow gas is changed to the air-fuel ratio (for example, near the theoretical air-fuel ratio) where the rich / lean output of the upstream oxygen sensor 25 is reversed. If the control amplitude of the air-fuel ratio F / B control is lowered, the control change width of the air-fuel ratio of the catalyst inflow gas becomes smaller and the control range of the air-fuel ratio of the catalyst inflow gas becomes narrower. . When the control range of the air-fuel ratio of the catalyst inflow gas is narrowed, the control range of the air-fuel ratio of the catalyst outflow gas is also narrowed, and it becomes difficult to control the air-fuel ratio of the catalyst outflow gas to the downstream target air-fuel ratio.

そこで、本実施例では、ＥＣＵ３８により後述する図７及び図８の出力特性変更制御用の各ルーチンを実行することで、下流側酸素センサ２６の出力に応じて上流側酸素センサ２５の出力特性を変更するように定電流回路４８を制御する。これにより、下流側酸素センサ２６の出力に応じて、上流側酸素センサ２５の出力に基づいた空燃比Ｆ／Ｂ制御の制御中心（上流側酸素センサ２５の出力のリッチ／リーンが反転する空燃比）を変更して、触媒流入ガスの空燃比の制御領域を拡大する。   Therefore, in this embodiment, the ECU 38 executes the output characteristic change control routines shown in FIGS. 7 and 8 to be described later, whereby the output characteristic of the upstream oxygen sensor 25 is changed according to the output of the downstream oxygen sensor 26. The constant current circuit 48 is controlled to change. As a result, the control center of the air-fuel ratio F / B control based on the output of the upstream oxygen sensor 25 (the air-fuel ratio at which the rich / lean of the output of the upstream oxygen sensor 25 is reversed) according to the output of the downstream oxygen sensor 26. ) To expand the control range of the air-fuel ratio of the catalyst inflow gas.

具体的には、図４に示すように、下流側酸素センサ２６の出力が下流側目標空燃比に相当する目標電圧（例えば０．７Ｖ）よりもリッチ側のときに、上流側酸素センサ２５のセンサ電極４３，４４間に正の定電流を流して、上流側酸素センサ２５の出力特性をリーン方向にシフトさせる（上流側酸素センサ２５の出力のリッチ／リーンが反転する変曲点をリーン方向にシフトさせる）ように定電流回路４８を制御する。これにより、上流側酸素センサ２５の出力に基づいた空燃比Ｆ／Ｂ制御の制御中心をリーン方向に変更して、触媒流入ガスの空燃比の制御領域をリーン方向に拡大する。   Specifically, as shown in FIG. 4, when the output of the downstream oxygen sensor 26 is richer than a target voltage (for example, 0.7 V) corresponding to the downstream target air-fuel ratio, the upstream oxygen sensor 25 A positive constant current is passed between the sensor electrodes 43 and 44 to shift the output characteristic of the upstream oxygen sensor 25 in the lean direction (the inflection point at which the rich / lean output of the upstream oxygen sensor 25 is reversed is in the lean direction. The constant current circuit 48 is controlled so as to be shifted to Thereby, the control center of the air-fuel ratio F / B control based on the output of the upstream oxygen sensor 25 is changed to the lean direction, and the control region of the air-fuel ratio of the catalyst inflow gas is expanded in the lean direction.

一方、下流側酸素センサ２６の出力が目標電圧よりもリーン側のときに、上流側酸素センサ２５のセンサ電極４３，４４間に負の定電流を流して、上流側酸素センサ２５の出力特性をリッチ方向にシフトさせる（上流側酸素センサ２５の出力のリッチ／リーンが反転する変曲点をリッチ方向にシフトさせる）ように定電流回路４８を制御する。これより、上流側酸素センサ２５の出力に基づいた空燃比Ｆ／Ｂ制御の制御中心をリッチ方向に変更して、触媒流入ガスの空燃比の制御領域をリッチ方向に拡大する。   On the other hand, when the output of the downstream oxygen sensor 26 is leaner than the target voltage, a negative constant current is allowed to flow between the sensor electrodes 43 and 44 of the upstream oxygen sensor 25, so that the output characteristics of the upstream oxygen sensor 25 are The constant current circuit 48 is controlled so as to shift in the rich direction (shift the inflection point at which the rich / lean output of the upstream oxygen sensor 25 reverses in the rich direction). Thus, the control center of the air-fuel ratio F / B control based on the output of the upstream oxygen sensor 25 is changed to the rich direction, and the control range of the air-fuel ratio of the catalyst inflow gas is expanded in the rich direction.

ところで、ＥＧＲ装置３１を備えたシステムでは、外部ＥＧＲ量（ＥＧＲガスの流量）に応じて排出ガス中の水素濃度が変化し、それに応じて上流側酸素センサ２５の出力特性にずれが生じる。   By the way, in the system provided with the EGR device 31, the hydrogen concentration in the exhaust gas changes according to the external EGR amount (EGR gas flow rate), and the output characteristics of the upstream oxygen sensor 25 deviate accordingly.

そこで、本実施例では、外部ＥＧＲ量に応じて上流側酸素センサ２５の出力特性を変更するように定電流回路４８を制御する。これにより、外部ＥＧＲ量に応じて排出ガス中の水素濃度が変化し、それに応じて上流側酸素センサ２５の出力特性にずれが生じるのに対応して上流側酸素センサ２５の出力特性を変更して上流側酸素センサ２５の出力特性を修正する。   Therefore, in this embodiment, the constant current circuit 48 is controlled so as to change the output characteristic of the upstream oxygen sensor 25 according to the external EGR amount. Thereby, the output characteristic of the upstream oxygen sensor 25 is changed in response to the change in the hydrogen concentration in the exhaust gas according to the amount of external EGR and the deviation in the output characteristic of the upstream oxygen sensor 25 accordingly. Then, the output characteristic of the upstream oxygen sensor 25 is corrected.

具体的には、図５に示すように、外部ＥＧＲ量が所定値よりも多いときに、上流側酸素センサ２５のセンサ電極４３，４４間に正の定電流を流して、上流側酸素センサ２５の出力特性をリーン方向にシフトさせるように定電流回路４８を制御する。これにより、外部ＥＧＲ量の増加（排出ガス中の水素濃度の増加）による上流側酸素センサ２５の出力特性のリッチ方向のずれを修正する。   Specifically, as shown in FIG. 5, when the external EGR amount is larger than a predetermined value, a positive constant current is passed between the sensor electrodes 43 and 44 of the upstream oxygen sensor 25, and the upstream oxygen sensor 25. The constant current circuit 48 is controlled so as to shift the output characteristic in the lean direction. As a result, the shift in the rich direction of the output characteristic of the upstream oxygen sensor 25 due to the increase in the external EGR amount (increase in the hydrogen concentration in the exhaust gas) is corrected.

また、吸気側可変バルブタイミング装置２９や排気側可変バルブタイミング装置３０を備えたシステムでは、吸気バルブ２７のバルブタイミング進角量や排気バルブ２８のバルブタイミング遅角量に応じてバルブオーバーラップ量が変化して内部ＥＧＲ量（筒内に残留する燃焼ガス量）が変化する。更に、内部ＥＧＲ量に応じて排出ガス中の水素濃度が変化し、それに応じて上流側酸素センサ２５の出力特性にずれが生じる。   In the system including the intake side variable valve timing device 29 and the exhaust side variable valve timing device 30, the valve overlap amount depends on the valve timing advance amount of the intake valve 27 and the valve timing delay amount of the exhaust valve 28. It changes and the amount of internal EGR (the amount of combustion gas remaining in the cylinder) changes. Furthermore, the hydrogen concentration in the exhaust gas changes according to the amount of internal EGR, and the output characteristics of the upstream oxygen sensor 25 are shifted accordingly.

そこで、本実施例では、吸気バルブ２７のバルブタイミング進角量と排気バルブ２８のバルブタイミング遅角量との和をバルブタイミング制御量とし、このバルブタイミング制御量に応じて上流側酸素センサ２５の出力特性を変更するように定電流回路４８を制御する。これにより、バルブタイミング制御量に応じて変化する内部ＥＧＲ量に応じて排出ガス中の水素濃度が変化し、それに応じて上流側酸素センサ２５の出力特性にずれが生じるのに対応して上流側酸素センサ２５の出力特性を変更して上流側酸素センサ２５の出力特性を修正する。   Therefore, in this embodiment, the sum of the valve timing advance amount of the intake valve 27 and the valve timing retard amount of the exhaust valve 28 is set as a valve timing control amount, and the upstream oxygen sensor 25 of the upstream side oxygen sensor 25 corresponds to this valve timing control amount. The constant current circuit 48 is controlled so as to change the output characteristics. As a result, the hydrogen concentration in the exhaust gas changes in accordance with the internal EGR amount that changes in accordance with the valve timing control amount, and the upstream side corresponding to the deviation in the output characteristics of the upstream oxygen sensor 25 accordingly. The output characteristic of the upstream oxygen sensor 25 is corrected by changing the output characteristic of the oxygen sensor 25.

具体的には、図６に示すように、バルブタイミング制御量が所定値よりも大きいときに、上流側酸素センサ２５のセンサ電極４３，４４間に正の定電流を流して、上流側酸素センサ２５の出力特性をリーン方向にシフトさせるように定電流回路４８を制御する。これにより、内部ＥＧＲ量の増加（排出ガス中の水素濃度の増加）による上流側酸素センサ２５の出力のリッチ方向のずれを修正する。   Specifically, as shown in FIG. 6, when the valve timing control amount is larger than a predetermined value, a positive constant current is caused to flow between the sensor electrodes 43 and 44 of the upstream oxygen sensor 25 and the upstream oxygen sensor. The constant current circuit 48 is controlled to shift the output characteristics of 25 in the lean direction. This corrects the shift in the rich direction of the output of the upstream oxygen sensor 25 due to an increase in the internal EGR amount (an increase in the hydrogen concentration in the exhaust gas).

尚、吸気側可変バルブタイミング装置２９のみを備えたシステムの場合には、吸気バルブ２７のバルブタイミング進角量をバルブタイミング制御量とする。また、排気側可変バルブタイミング装置３０のみを備えたシステムの場合には、排気バルブ２８のバルブタイミング進角量をバルブタイミング制御量とする。   In the case of a system including only the intake side variable valve timing device 29, the valve timing advance amount of the intake valve 27 is set as a valve timing control amount. Further, in the case of a system including only the exhaust side variable valve timing device 30, the valve timing advance amount of the exhaust valve 28 is set as a valve timing control amount.

また、本実施例では、後述する図９の触媒暖機制御ルーチンを実行することで、触媒暖機要求が発生したときに、触媒２４の暖機を促進する触媒暖機制御を実行する。この触媒暖機制御では、エンジン１１に供給する混合気の空燃比を理論空燃比よりもリーンに制御するリーン燃焼制御を行うと共に、点火時期を遅角する点火時期遅角制御を行って、排出ガスの温度を上昇させる。更に、触媒暖機制御の実行中に、上流側酸素センサ２５のセンサ電極４３，４４間に正の定電流を流して、上流側酸素センサ２５の出力特性をリーン方向にシフトさせるように定電流回路４８を制御する。これにより、リーン燃焼制御を行う触媒暖機制御の実行中に、上流側酸素センサ２５の出力に基づいた空燃比の制御領域をリーン方向にシフトさせて、リーン燃焼制御を精度良く行うことができるようにする。
以下、ＥＣＵ３８が実行する図７乃至図９の各ルーチンの処理内容を説明する。 In this embodiment, a catalyst warm-up control for promoting warm-up of the catalyst 24 is executed when a catalyst warm-up request is generated by executing a catalyst warm-up control routine of FIG. 9 described later. In this catalyst warm-up control, lean combustion control for controlling the air-fuel ratio of the air-fuel mixture supplied to the engine 11 to be leaner than the stoichiometric air-fuel ratio is performed, and ignition timing retarding control for retarding the ignition timing is performed. Increase gas temperature. Further, during the catalyst warm-up control, a constant positive current is passed between the sensor electrodes 43 and 44 of the upstream oxygen sensor 25 to shift the output characteristic of the upstream oxygen sensor 25 in the lean direction. The circuit 48 is controlled. Thus, during the catalyst warm-up control for performing the lean combustion control, the air-fuel ratio control region based on the output of the upstream oxygen sensor 25 is shifted in the lean direction, so that the lean combustion control can be performed with high accuracy. Like that.
The processing contents of the routines shown in FIGS. 7 to 9 executed by the ECU 38 will be described below.

［出力特性変更制御メインルーチン］
図７に示す出力特性変更制御メインルーチンは、ＥＣＵ３８の電源オン期間中（イグニッションスイッチのオン期間中）に所定周期で繰り返し実行され、特許請求の範囲でいう出力特性変更制御手段としての役割を果たす。本ルーチンが起動されると、まず、ステップ１０１で、空燃比Ｆ／Ｂ制御が開始されたか否かを判定し、空燃比Ｆ／Ｂ制御がまだ開始されていなければ、そのまま本ルーチンを終了する。 [Output characteristics change control main routine]
The output characteristic change control main routine shown in FIG. 7 is repeatedly executed at a predetermined period during the power-on period of the ECU 38 (while the ignition switch is on), and serves as output characteristic change control means in the claims. . When this routine is started, first, at step 101, it is determined whether or not the air-fuel ratio F / B control has been started. If the air-fuel ratio F / B control has not yet been started, this routine is terminated as it is. .

その後、上記ステップ１０１で、空燃比Ｆ／Ｂ制御が開始されたと判定された場合には、ステップ１０２に進み、サブＦ／Ｂ制御が開始されたか否かを判定し、サブＦ／Ｂ制御がまだ開始されていなければ、そのまま本ルーチンを終了する。   Thereafter, if it is determined in step 101 that the air-fuel ratio F / B control has been started, the process proceeds to step 102 to determine whether or not the sub F / B control has been started, and the sub F / B control is performed. If it has not started yet, this routine is terminated.

その後、上記ステップ１０２で、サブＦ／Ｂ制御が開始されたと判定された場合には、ステップ１０３に進み、後述する図８の出力特性変更制御ルーチンを実行することで、下流側酸素センサ２６の出力、外部ＥＧＲ量、バルブタイミング制御量に応じて、上流側酸素センサ２５の出力特性を変更する。   Thereafter, if it is determined in step 102 that the sub-F / B control has been started, the process proceeds to step 103, and an output characteristic change control routine of FIG. The output characteristics of the upstream oxygen sensor 25 are changed according to the output, the external EGR amount, and the valve timing control amount.

［出力特性変更制御ルーチン］
図８に示す出力特性変更制御ルーチンは、前記図７の出力特性変更制御メインルーチンのステップ１０３で実行されるサブルーチンである。本ルーチンが起動されると、まず、ステップ２０１で、下流側酸素センサ２６の出力が目標電圧（例えば０．７Ｖ）よりもリッチ側であるか否か（つまり触媒流出ガスの空燃比が下流側目標空燃比よりもリッチであるか否か）を判定する。 [Output characteristics change control routine]
The output characteristic change control routine shown in FIG. 8 is a subroutine executed in step 103 of the output characteristic change control main routine of FIG. When this routine is started, first, at step 201, whether or not the output of the downstream oxygen sensor 26 is richer than the target voltage (for example, 0.7V) (that is, the air-fuel ratio of the catalyst outflow gas is downstream). It is determined whether or not the air-fuel ratio is richer than the target air-fuel ratio.

このステップ２０１で、下流側酸素センサ２６の出力が目標電圧よりもリッチ側であると判定された場合には、ステップ２０２に進み、上流側酸素センサ２５のセンサ電極４３，４４間に正の定電流を流して、上流側酸素センサ２５の出力特性をリーン方向にシフトさせるように定電流回路４８を制御する。この場合、上流側酸素センサ２５のセンサ電極４３，４４間に流す正の定電流は、所定値に設定（固定）しても良いし、下流側酸素センサ２６の出力又はサブＦ／Ｂ補正量に応じて変化させるようにしても良い。   If it is determined in step 201 that the output of the downstream oxygen sensor 26 is richer than the target voltage, the routine proceeds to step 202, where a positive constant is established between the sensor electrodes 43 and 44 of the upstream oxygen sensor 25. The constant current circuit 48 is controlled so as to shift the output characteristic of the upstream oxygen sensor 25 in the lean direction by supplying a current. In this case, the positive constant current flowing between the sensor electrodes 43 and 44 of the upstream oxygen sensor 25 may be set (fixed) to a predetermined value, or the output of the downstream oxygen sensor 26 or the sub F / B correction amount. You may make it change according to.

一方、上記ステップ２０１で、下流側酸素センサ２６の出力が目標電圧よりもリッチ側ではないと判定された場合には、ステップ２０３に進み、下流側酸素センサ２６の出力が目標電圧よりもリーン側であるか否か（つまり触媒流出ガスの空燃比が下流側目標空燃比よりもリーンであるか否か）を判定する。   On the other hand, if it is determined in step 201 that the output of the downstream oxygen sensor 26 is not richer than the target voltage, the process proceeds to step 203 where the output of the downstream oxygen sensor 26 is leaner than the target voltage. (That is, whether the air-fuel ratio of the catalyst outflow gas is leaner than the downstream target air-fuel ratio).

このステップ２０３で、下流側酸素センサ２６の出力が目標電圧よりもリーン側であると判定された場合には、ステップ２０４に進み、上流側酸素センサ２５のセンサ電極４３，４４間に負の定電流を流して、上流側酸素センサ２５の出力特性をリッチ方向にシフトさせるように定電流回路４８を制御する。この場合、上流側酸素センサ２５のセンサ電極４３，４４間に流す負の定電流は、所定値に設定（固定）しても良いし、下流側酸素センサ２６の出力又はサブＦ／Ｂ補正量に応じて変化させるようにしても良い。   If it is determined in step 203 that the output of the downstream oxygen sensor 26 is leaner than the target voltage, the process proceeds to step 204 where a negative constant is set between the sensor electrodes 43 and 44 of the upstream oxygen sensor 25. The constant current circuit 48 is controlled so as to shift the output characteristic of the upstream oxygen sensor 25 in the rich direction by supplying a current. In this case, the negative constant current flowing between the sensor electrodes 43 and 44 of the upstream oxygen sensor 25 may be set (fixed) to a predetermined value, or the output of the downstream oxygen sensor 26 or the sub F / B correction amount. You may make it change according to.

尚、上記ステップ２０１と上記ステップ２０３で両方とも「Ｎｏ」と判定された場合（下流側酸素センサ２６の出力が目標電圧と一致する場合）には、上流側酸素センサ２５の出力特性を現在の状態に維持するように定電流回路４８を制御する。或は、上流側酸素センサ２５の出力特性を変更していない通常状態に戻すように定電流回路４８を制御する（定電流を０にする）ようにしても良い。   In addition, when both of the above step 201 and step 203 are determined “No” (when the output of the downstream oxygen sensor 26 matches the target voltage), the output characteristics of the upstream oxygen sensor 25 are set to the current values. The constant current circuit 48 is controlled to maintain the state. Alternatively, the constant current circuit 48 may be controlled so that the output characteristic of the upstream oxygen sensor 25 is returned to the normal state in which the output characteristic is not changed (the constant current is set to 0).

この後、ステップ２０５に進み、外部ＥＧＲ量が所定値よりも多いか否かを、例えば、ＥＧＲ弁３３の開度が所定開度よりも大きいか否かによって判定する。
このステップ２０５で、外部ＥＧＲ量が所定値よりも多いと判定された場合には、ステップ２０６に進み、上流側酸素センサ２５のセンサ電極４３，４４間に正の定電流を流して、上流側酸素センサ２５の出力特性をリーン方向にシフトさせるように定電流回路４８を制御する。この場合、上流側酸素センサ２５のセンサ電極４３，４４間に流す正の定電流は、所定値に設定（固定）しても良いし、外部ＥＧＲ量（例えばＥＧＲ弁３３の開度）に応じて変化させるようにしても良い。 Thereafter, the routine proceeds to step 205, where it is determined whether or not the external EGR amount is larger than a predetermined value, for example, based on whether or not the opening degree of the EGR valve 33 is larger than the predetermined opening degree.
If it is determined in step 205 that the external EGR amount is greater than the predetermined value, the process proceeds to step 206 where a positive constant current is passed between the sensor electrodes 43 and 44 of the upstream oxygen sensor 25 and the upstream side The constant current circuit 48 is controlled to shift the output characteristic of the oxygen sensor 25 in the lean direction. In this case, the positive constant current flowing between the sensor electrodes 43 and 44 of the upstream oxygen sensor 25 may be set (fixed) to a predetermined value or according to the external EGR amount (for example, the opening degree of the EGR valve 33). May be changed.

一方、上記ステップ２０５で、外部ＥＧＲ量が所定値よりも多くはないと判定された場合には、ステップ２０７に進み、外部ＥＧＲ量が所定値よりも少ないか否かを、例えば、ＥＧＲ弁３３の開度が所定開度よりも小さいか否かによって判定する。   On the other hand, if it is determined in step 205 that the external EGR amount is not larger than the predetermined value, the process proceeds to step 207, where it is determined whether the external EGR amount is smaller than the predetermined value, for example, the EGR valve 33 Is determined based on whether or not the opening degree is smaller than a predetermined opening degree.

このステップ２０７で、外部ＥＧＲ量が所定値よりも少ないと判定された場合には、ステップ２０８に進み、上流側酸素センサ２５のセンサ電極４３，４４間に負の定電流を流して、上流側酸素センサ２５の出力特性をリッチ方向にシフトさせるように定電流回路４８を制御する。この場合、上流側酸素センサ２５のセンサ電極４３，４４間に流す負の定電流は、所定値に設定（固定）しても良いし、外部ＥＧＲ量（例えばＥＧＲ弁３３の開度）に応じて変化させるようにしても良い。   If it is determined in step 207 that the external EGR amount is smaller than the predetermined value, the process proceeds to step 208 where a negative constant current is passed between the sensor electrodes 43 and 44 of the upstream oxygen sensor 25 and the upstream side The constant current circuit 48 is controlled to shift the output characteristics of the oxygen sensor 25 in the rich direction. In this case, the negative constant current that flows between the sensor electrodes 43 and 44 of the upstream oxygen sensor 25 may be set (fixed) to a predetermined value or according to the external EGR amount (for example, the opening degree of the EGR valve 33). May be changed.

尚、上記ステップ２０５と上記ステップ２０７で両方とも「Ｎｏ」と判定された場合（外部ＥＧＲ量が所定値と一致する場合）には、上流側酸素センサ２５の出力特性を現在の状態に維持するように定電流回路４８を制御する。或は、上流側酸素センサ２５の出力特性を変更していない通常状態に戻すように定電流回路４８を制御する（定電流を０にする）ようにしても良い。   In addition, when both of the above step 205 and step 207 are determined “No” (when the external EGR amount matches a predetermined value), the output characteristic of the upstream oxygen sensor 25 is maintained in the current state. The constant current circuit 48 is controlled as described above. Alternatively, the constant current circuit 48 may be controlled so that the output characteristic of the upstream oxygen sensor 25 is returned to the normal state in which the output characteristic is not changed (the constant current is set to 0).

この後、ステップ２０９に進み、バルブタイミング制御量（例えば吸気バルブ２７のバルブタイミング進角量と排気バルブ２８のバルブタイミング遅角量との和）が所定値よりも大きいか否かを判定する。   Thereafter, the routine proceeds to step 209, where it is determined whether or not the valve timing control amount (for example, the sum of the valve timing advance amount of the intake valve 27 and the valve timing retard amount of the exhaust valve 28) is larger than a predetermined value.

このステップ２０９で、バルブタイミング制御量が所定値よりも大きいと判定された場合には、ステップ２１０に進み、上流側酸素センサ２５のセンサ電極４３，４４間に正の定電流を流して、上流側酸素センサ２５の出力特性をリーン方向にシフトさせるように定電流回路４８を制御する。この場合、上流側酸素センサ２５のセンサ電極４３，４４間に流す正の定電流は、所定値に設定（固定）しても良いし、バルブタイミング制御量に応じて変化させるようにしても良い。   If it is determined in step 209 that the valve timing control amount is larger than the predetermined value, the process proceeds to step 210 where a positive constant current is passed between the sensor electrodes 43 and 44 of the upstream oxygen sensor 25 and the upstream side. The constant current circuit 48 is controlled to shift the output characteristic of the side oxygen sensor 25 in the lean direction. In this case, the positive constant current that flows between the sensor electrodes 43 and 44 of the upstream oxygen sensor 25 may be set (fixed) to a predetermined value, or may be changed according to the valve timing control amount. .

一方、上記ステップ２０９で、バルブタイミング制御量が所定値よりも大きくはないと判定された場合には、ステップ２１１に進み、バルブタイミング制御量が所定値よりも小さいか否かを判定する。   On the other hand, if it is determined in step 209 that the valve timing control amount is not greater than the predetermined value, the process proceeds to step 211 to determine whether or not the valve timing control amount is smaller than the predetermined value.

このステップ２１１で、バルブタイミング制御量が所定値よりも小さいと判定された場合には、ステップ２１２に進み、上流側酸素センサ２５のセンサ電極４３，４４間に負の定電流を流して、上流側酸素センサ２５の出力特性をリッチ方向にシフトさせるように定電流回路４８を制御する。この場合、上流側酸素センサ２５のセンサ電極４３，４４間に流す負の定電流は、所定値に設定（固定）しても良いし、バルブタイミング制御量に応じて変化させるようにしても良い。   If it is determined in step 211 that the valve timing control amount is smaller than the predetermined value, the process proceeds to step 212 where a negative constant current is passed between the sensor electrodes 43 and 44 of the upstream oxygen sensor 25 and the upstream side. The constant current circuit 48 is controlled to shift the output characteristic of the side oxygen sensor 25 in the rich direction. In this case, the negative constant current flowing between the sensor electrodes 43 and 44 of the upstream oxygen sensor 25 may be set (fixed) to a predetermined value, or may be changed according to the valve timing control amount. .

尚、上記ステップ２０９と上記ステップ２１１で両方とも「Ｎｏ」と判定された場合（バルブタイミング制御量が所定値と一致する場合）には、上流側酸素センサ２５の出力特性を現在の状態に維持するように定電流回路４８を制御する。或は、上流側酸素センサ２５の出力特性を変更していない通常状態に戻すように定電流回路４８を制御する（定電流を０にする）ようにしても良い。   Note that if both of the above step 209 and step 211 are determined “No” (when the valve timing control amount matches the predetermined value), the output characteristic of the upstream oxygen sensor 25 is maintained in the current state. Thus, the constant current circuit 48 is controlled. Alternatively, the constant current circuit 48 may be controlled so that the output characteristic of the upstream oxygen sensor 25 is returned to the normal state in which the output characteristic is not changed (the constant current is set to 0).

［触媒暖機制御ルーチン］
図９に示す触媒暖機制御ルーチンは、ＥＣＵ３８の電源オン期間中（イグニッションスイッチのオン期間中）に所定周期で繰り返し実行され、特許請求の範囲でいう触媒暖機制御手段としての役割を果たす。本ルーチンが起動されると、まず、ステップ３０１で、空燃比Ｆ／Ｂ制御が開始されたか否かを判定し、空燃比Ｆ／Ｂ制御がまだ開始されていなければ、そのまま本ルーチンを終了する。 [Catalyst warm-up control routine]
The catalyst warm-up control routine shown in FIG. 9 is repeatedly executed at a predetermined cycle during the power-on period of the ECU 38 (while the ignition switch is on), and serves as catalyst warm-up control means in the claims. When this routine is started, first, at step 301, it is determined whether or not the air-fuel ratio F / B control has been started. If the air-fuel ratio F / B control has not yet been started, this routine is terminated as it is. .

その後、上記ステップ３０１で、空燃比Ｆ／Ｂ制御が開始されたと判定された場合には、ステップ３０２に進み、触媒暖機要求が発生しているか否かを、例えば、触媒２４の温度（検出値又は推定値）が活性温度よりも低いか否か等によって判定する。触媒暖機要求が発生していなければ、そのまま本ルーチンを終了する。   Thereafter, if it is determined in step 301 that the air-fuel ratio F / B control has been started, the process proceeds to step 302 to determine whether or not a catalyst warm-up request has occurred, for example, the temperature of the catalyst 24 (detection). Value or estimated value) is determined by whether or not the temperature is lower than the activation temperature. If no catalyst warm-up request has been generated, this routine is terminated.

一方、上記ステップ３０２で、触媒暖機要求が発生していると判定された場合には、ステップ３０３に進み、触媒２４の暖機を促進する触媒暖機制御を実行する。この触媒暖機制御では、エンジン１１に供給する混合気の空燃比を理論空燃比よりもリーンに制御するリーン燃焼制御を行うと共に、点火時期を遅角する点火時期遅角制御を行って、排出ガスの温度を上昇させる。   On the other hand, if it is determined in step 302 that a catalyst warm-up request has been generated, the process proceeds to step 303, where catalyst warm-up control for promoting warm-up of the catalyst 24 is executed. In this catalyst warm-up control, lean combustion control for controlling the air-fuel ratio of the air-fuel mixture supplied to the engine 11 to be leaner than the stoichiometric air-fuel ratio is performed, and ignition timing retarding control for retarding the ignition timing is performed. Increase gas temperature.

この後、ステップ３０４に進み、触媒暖機制御の実行中に、上流側酸素センサ２５のセンサ電極４３，４４間に正の定電流を流して、上流側酸素センサ２５の出力特性をリーン方向にシフトさせるように定電流回路４８を制御する。この場合、上流側酸素センサ２５のセンサ電極４３，４４間に流す正の定電流は、所定値に設定（固定）する。   Thereafter, the process proceeds to step 304, and during the execution of the catalyst warm-up control, a positive constant current is passed between the sensor electrodes 43 and 44 of the upstream oxygen sensor 25, and the output characteristic of the upstream oxygen sensor 25 is made lean. The constant current circuit 48 is controlled to shift. In this case, the positive constant current flowing between the sensor electrodes 43 and 44 of the upstream oxygen sensor 25 is set (fixed) to a predetermined value.

この後、ステップ３０５に進み、触媒２４の暖機が完了したか否かを、例えば、触媒２４の温度（検出値又は推定値）が活性温度以上に上昇したか否か、或は、触媒暖機制御を開始してから所定時間以上が経過したか否か等によって判定する。   Thereafter, the process proceeds to step 305, where it is determined whether or not the warming-up of the catalyst 24 has been completed, for example, whether or not the temperature of the catalyst 24 (detected value or estimated value) has risen to the activation temperature or higher, or Judgment is made based on whether or not a predetermined time has elapsed since the start of machine control.

このステップ３０５で、触媒２４の暖機がまだ完了していないと判定された場合には、ステップ３０６に進み、エンジン回転変動（例えばエンジン回転速度の今回値と前回値との差）が所定値以上であるか否かを判定する。   If it is determined in step 305 that the warm-up of the catalyst 24 has not yet been completed, the process proceeds to step 306, where the engine speed fluctuation (for example, the difference between the current value of the engine speed and the previous value) is a predetermined value. It is determined whether it is above.

このステップ３０６で、エンジン回転変動が所定値よりも小さいと判定された場合には、ステップ３０７に進み、排出ガスの温度（検出値又は推定値）が所定値以上であるか否かを判定する。
このステップ３０７で、排出ガスの温度が所定値よりも低いと判定された場合には、そのまま本ルーチンを終了する。 If it is determined in step 306 that the engine rotation fluctuation is smaller than the predetermined value, the process proceeds to step 307, where it is determined whether or not the exhaust gas temperature (detected value or estimated value) is equal to or higher than the predetermined value. .
If it is determined in step 307 that the temperature of the exhaust gas is lower than the predetermined value, this routine is terminated as it is.

その後、上記ステップ３０５〜３０７のいずれかで「Ｙｅｓ」と判定された場合には、触媒暖機制御の終了条件が成立したと判断して、ステップ３０８に進み、触媒暖機制御（リーン燃焼制御及び点火時期遅角制御）を終了した後、ステップ３０９に進み、上流側酸素センサ２５の出力特性を変更していない通常状態に戻すように定電流回路４８を制御する（定電流を０にする）。
この図９のルーチンのステップ３０４及びステップ３０９の処理も特許請求の範囲でいう出力特性変更制御手段としての役割を果たす。 Thereafter, when it is determined “Yes” in any of the above steps 305 to 307, it is determined that the catalyst warm-up control end condition is satisfied, and the process proceeds to step 308, where the catalyst warm-up control (lean combustion control) is performed. Then, the process proceeds to step 309, and the constant current circuit 48 is controlled so as to return to the normal state in which the output characteristics of the upstream oxygen sensor 25 are not changed (the constant current is set to 0). ).
The processing of step 304 and step 309 in the routine of FIG. 9 also serves as output characteristic change control means in the claims.

以上説明した本実施例では、下流側酸素センサ２６の出力が目標電圧よりもリッチ側のときに、上流側酸素センサ２５の出力特性をリーン方向にシフトさせるように定電流回路４８を制御する。これにより、上流側酸素センサ２５の出力に基づいた空燃比Ｆ／Ｂ制御の制御中心をリーン方向に変更して、触媒流入ガスの空燃比の制御領域をリーン方向に拡大することができる。一方、下流側酸素センサ２６の出力が目標電圧よりもリーン側のときに、上流側酸素センサ２５の出力特性をリッチ方向にシフトさせるように定電流回路４８を制御する。これより、上流側酸素センサ２５の出力に基づいた空燃比Ｆ／Ｂ制御の制御中心をリッチ方向に変更して、触媒流入ガスの空燃比の制御領域をリッチ方向に拡大することができる。   In the present embodiment described above, the constant current circuit 48 is controlled so that the output characteristic of the upstream oxygen sensor 25 is shifted in the lean direction when the output of the downstream oxygen sensor 26 is richer than the target voltage. Thereby, the control center of the air-fuel ratio F / B control based on the output of the upstream oxygen sensor 25 can be changed to the lean direction, and the control range of the air-fuel ratio of the catalyst inflow gas can be expanded in the lean direction. On the other hand, when the output of the downstream oxygen sensor 26 is leaner than the target voltage, the constant current circuit 48 is controlled so as to shift the output characteristic of the upstream oxygen sensor 25 in the rich direction. Thus, the control center of the air-fuel ratio F / B control based on the output of the upstream oxygen sensor 25 can be changed to the rich direction, and the control range of the air-fuel ratio of the catalyst inflow gas can be expanded in the rich direction.

このように、下流側酸素センサ２６の出力に応じて上流側酸素センサ２５の出力特性を変更することで、上流側酸素センサ２５の出力に基づいた空燃比Ｆ／Ｂ制御の制御中心を変更して、触媒流入ガスの空燃比の制御領域を拡大することができる。その結果、触媒流出ガスの空燃比の制御領域も拡大することができ、触媒流出ガスの空燃比を目標空燃比に制御することが可能となる。   Thus, by changing the output characteristics of the upstream oxygen sensor 25 according to the output of the downstream oxygen sensor 26, the control center of the air-fuel ratio F / B control based on the output of the upstream oxygen sensor 25 is changed. Thus, the control range of the air-fuel ratio of the catalyst inflow gas can be expanded. As a result, the control range of the air / fuel ratio of the catalyst outflow gas can be expanded, and the air / fuel ratio of the catalyst outflow gas can be controlled to the target air / fuel ratio.

また、本実施例では、上流側酸素センサ２５のセンサ電極４３，４４間に定電流を流して上流側酸素センサ２５の出力特性を変更する定電流回路４８を設けるようにしたので、定電流回路４８によりセンサ電極４３，４４間に定電流を流すという簡単な方法で上流側酸素センサ２５の出力特性を変更することができる。しかも、上流側酸素センサ２５の大幅な設計変更やコストアップを招くことなく、上流側酸素センサ２５の出力特性を変更することができる。   In the present embodiment, the constant current circuit 48 for changing the output characteristics of the upstream oxygen sensor 25 by passing a constant current between the sensor electrodes 43 and 44 of the upstream oxygen sensor 25 is provided. 48, the output characteristic of the upstream oxygen sensor 25 can be changed by a simple method of passing a constant current between the sensor electrodes 43 and 44. In addition, the output characteristics of the upstream oxygen sensor 25 can be changed without causing a significant design change or cost increase of the upstream oxygen sensor 25.

また、本実施例では、外部ＥＧＲ量が所定値よりも多いときに、上流側酸素センサ２５の出力特性をリーン方向にシフトさせるように定電流回路４８を制御するようにしたので、外部ＥＧＲ量の増加（排出ガス中の水素濃度の増加）による上流側酸素センサ２５の出力特性のリッチ方向のずれを修正することができる。   In this embodiment, when the external EGR amount is larger than the predetermined value, the constant current circuit 48 is controlled so as to shift the output characteristic of the upstream oxygen sensor 25 in the lean direction. The deviation in the rich direction of the output characteristic of the upstream oxygen sensor 25 due to the increase in the amount of hydrogen (the increase in the hydrogen concentration in the exhaust gas) can be corrected.

更に、本実施例では、バルブタイミング制御量に応じて内部ＥＧＲ量が変化することを考慮して、バルブタイミング制御量が所定値よりも大きいときに、上流側酸素センサ２５の出力特性をリーン方向にシフトさせるように定電流回路４８を制御するようにしたので、内部ＥＧＲ量の増加（排出ガス中の水素濃度の増加）による上流側酸素センサ２５の出力のリッチ方向のずれを修正することができる。   Furthermore, in the present embodiment, considering that the internal EGR amount changes according to the valve timing control amount, when the valve timing control amount is larger than a predetermined value, the output characteristic of the upstream oxygen sensor 25 is set in the lean direction. Since the constant current circuit 48 is controlled so as to shift to, the shift in the rich direction of the output of the upstream oxygen sensor 25 due to the increase in the internal EGR amount (increase in the hydrogen concentration in the exhaust gas) can be corrected. it can.

また、本実施例では、リーン燃焼制御を行う触媒暖機制御の実行中に、上流側酸素センサ２５の出力特性をリーン方向にシフトさせるように定電流回路４８を制御するようにしたので、リーン燃焼制御を行う触媒暖機制御の実行中に、上流側酸素センサ２５の出力に基づいた空燃比の制御領域をリーン方向にシフトさせることができ、リーン燃焼制御を精度良く行うことができる。   In this embodiment, the constant current circuit 48 is controlled so as to shift the output characteristic of the upstream oxygen sensor 25 in the lean direction during the catalyst warm-up control for performing the lean combustion control. During the execution of the catalyst warm-up control that performs the combustion control, the control range of the air-fuel ratio based on the output of the upstream oxygen sensor 25 can be shifted in the lean direction, and the lean combustion control can be performed with high accuracy.

尚、上記実施例では、上流側酸素センサ２５（センサ素子４１）の大気側電極層４４に定電流回路４８を接続する構成としたが、これに限定されず、例えば、上流側酸素センサ２５（センサ素子４１）の排気側電極層４３に定電流回路４８を接続する構成としたり、或は、排気側電極層４３と大気側電極層４４の両方に定電流回路４８を接続する構成としても良い。   In the above embodiment, the constant current circuit 48 is connected to the atmosphere-side electrode layer 44 of the upstream oxygen sensor 25 (sensor element 41). However, the present invention is not limited to this. For example, the upstream oxygen sensor 25 ( The constant current circuit 48 may be connected to the exhaust side electrode layer 43 of the sensor element 41), or the constant current circuit 48 may be connected to both the exhaust side electrode layer 43 and the atmosphere side electrode layer 44. .

また、上記実施例では、コップ型構造のセンサ素子４１を有する酸素センサ２５を用いた構成としたが、これに限定されず、例えば、積層構造型のセンサ素子を有する酸素センサを用いた構成としても良い。   Moreover, in the said Example, although it was set as the structure using the oxygen sensor 25 which has the sensor element 41 of a cup type structure, it is not limited to this, For example, as a structure using the oxygen sensor which has a sensor element of a laminated structure type Also good.

また、上記実施例では、上流側酸素センサ２５の出力特性を変更するようにしたが、更に、下流側酸素センサ２６のセンサ電極間に定電流を流す定電流回路を設けて、下流側酸素センサ２６の出力特性を変更する構成としても良い。   In the above-described embodiment, the output characteristic of the upstream oxygen sensor 25 is changed. However, a constant current circuit for supplying a constant current between the sensor electrodes of the downstream oxygen sensor 26 is further provided, and the downstream oxygen sensor is provided. A configuration in which the output characteristics of 26 are changed is also possible.

また、下流側酸素センサ２６に代えて、触媒流出ガスの空燃比を検出する空燃比センサ（空燃比に応じたリニアな空燃比信号を出力するセンサ）を設けた構成としても良い。或は、下流側酸素センサ２６を省略して、例えば、触媒２４の性能を模擬したモデルを用いて触媒流出ガスの空燃比を推定する構成としても良い。   Instead of the downstream oxygen sensor 26, an air-fuel ratio sensor for detecting the air-fuel ratio of the catalyst outflow gas (a sensor for outputting a linear air-fuel ratio signal corresponding to the air-fuel ratio) may be provided. Alternatively, the downstream oxygen sensor 26 may be omitted, and the air-fuel ratio of the catalyst outflow gas may be estimated using a model that simulates the performance of the catalyst 24, for example.

その他、本発明は、図１に示すような吸気ポート噴射式エンジンに限定されず、筒内噴射式エンジンや、吸気ポート噴射用の燃料噴射弁と筒内噴射用の燃料噴射弁の両方を備えたデュアル噴射式のエンジンにも適用して実施できる。   In addition, the present invention is not limited to the intake port injection type engine as shown in FIG. 1, but includes an in-cylinder injection type engine, and both an intake port injection fuel injection valve and an in-cylinder injection fuel injection valve. It can also be applied to dual-injection engines.

１１…エンジン（内燃機関）、２４…触媒、２５…上流側酸素センサ（上流側センサ）、２６…下流側酸素センサ（下流側空燃比取得手段）、３８…ＥＣＵ（出力特性変更制御手段，触媒暖機制御手段）、４８…定電流回路（出力特性変更手段）   DESCRIPTION OF SYMBOLS 11 ... Engine (internal combustion engine), 24 ... Catalyst, 25 ... Upstream oxygen sensor (upstream sensor), 26 ... Downstream oxygen sensor (downstream air-fuel ratio acquisition means), 38 ... ECU (output characteristic change control means, catalyst) Warm-up control means), 48 ... constant current circuit (output characteristic changing means)

Claims (10)

内燃機関（１１）の排出ガスを浄化する触媒（２４）と、該触媒（２４）の上流側の排出ガスの空燃比のリッチ／リーンを検出する上流側センサ（２５）と、前記触媒（２４）の下流側の排出ガスの空燃比を検出又は推定する下流側空燃比取得手段（２６）とを備え、前記上流側センサ（２５）の出力に基づいて空燃比フィードバック制御を行う内燃機関の空燃比制御装置において、
前記上流側センサ（２５）の出力特性を変更する出力特性変更手段（４８）と、
前記下流側空燃比取得手段（２６）の出力に応じて前記上流側センサ（２５）の出力特性を変更するように前記出力特性変更手段（４８）を制御する出力特性変更制御手段（３８）と
を備えていることを特徴とする内燃機関の空燃比制御装置。 A catalyst (24) for purifying exhaust gas of the internal combustion engine (11), an upstream sensor (25) for detecting rich / lean air-fuel ratio of exhaust gas upstream of the catalyst (24), and the catalyst (24 ) Downstream air-fuel ratio acquisition means (26) for detecting or estimating the air-fuel ratio of the exhaust gas on the downstream side of the internal combustion engine that performs air-fuel ratio feedback control based on the output of the upstream sensor (25). In the fuel ratio control device,
Output characteristic changing means (48) for changing the output characteristic of the upstream sensor (25);
An output characteristic change control means (38) for controlling the output characteristic change means (48) so as to change the output characteristic of the upstream sensor (25) in accordance with the output of the downstream air-fuel ratio acquisition means (26). An air-fuel ratio control apparatus for an internal combustion engine, comprising: 前記出力特性変更制御手段（３８）は、前記下流側空燃比取得手段（２６）の出力が目標値よりもリッチ側のときに前記上流側センサ（２５）の出力のリッチ／リーンが反転する変曲点をリーン方向にシフトさせるように前記出力特性変更手段（４８）を制御し、前記下流側空燃比取得手段（２６）の出力が前記目標値よりもリーン側のときに前記変曲点をリッチ方向にシフトさせるように前記出力特性変更手段（４８）を制御することを特徴とする請求項１に記載の内燃機関の空燃比制御装置。   The output characteristic change control means (38) is a change that reverses the rich / lean output of the upstream sensor (25) when the output of the downstream air-fuel ratio acquisition means (26) is richer than a target value. The output characteristic changing means (48) is controlled so as to shift the inflection point in the lean direction, and the inflection point is set when the output of the downstream air-fuel ratio acquisition means (26) is leaner than the target value. The air-fuel ratio control apparatus for an internal combustion engine according to claim 1, wherein the output characteristic changing means (48) is controlled to shift in a rich direction. 前記上流側センサ（２５）は、一対のセンサ電極（４３，４４）間に固体電解質体（４２）が配置されたセンサ素子（４１）を有し、
前記出力特性変更手段（４８）は、前記センサ電極（４３，４４）間に定電流を流して前記上流側センサ（２５）の出力特性を変更することを特徴とする請求項１又は２に記載の内燃機関の空燃比制御装置。 The upstream sensor (25) includes a sensor element (41) in which a solid electrolyte body (42) is disposed between a pair of sensor electrodes (43, 44),
The output characteristic changing means (48) changes the output characteristic of the upstream sensor (25) by causing a constant current to flow between the sensor electrodes (43, 44). An air-fuel ratio control apparatus for an internal combustion engine. 前記下流側空燃比取得手段（２６）は、前記触媒（２４）の下流側の排出ガスの空燃比又はリッチ／リーンを検出するセンサであることを特徴とする請求項１乃至３のいずれかに記載の内燃機関の空燃比制御装置。   4. The downstream air-fuel ratio acquisition means (26) is a sensor that detects an air-fuel ratio or rich / lean of exhaust gas downstream of the catalyst (24). An air-fuel ratio control apparatus for an internal combustion engine as described. 前記内燃機関（１１）の排出ガスの一部をＥＧＲガスとして吸気側へ還流させるＥＧＲ装置（３１）を備え、
前記出力特性変更制御手段（３８）は、前記ＥＧＲガスの流量に応じて前記上流側センサ（２５）の出力特性を変更するように前記出力特性変更手段（４８）を制御することを特徴とする請求項１乃至４のいずれかに記載の内燃機関の空燃比制御装置。 An EGR device (31) for recirculating a part of the exhaust gas of the internal combustion engine (11) to the intake side as EGR gas;
The output characteristic change control means (38) controls the output characteristic change means (48) so as to change the output characteristic of the upstream sensor (25) according to the flow rate of the EGR gas. The air-fuel ratio control apparatus for an internal combustion engine according to any one of claims 1 to 4. 前記出力特性変更制御手段（３８）は、前記ＥＧＲガスの流量が所定値よりも多いときに前記上流側センサ（２５）の出力のリッチ／リーンが反転する変曲点をリーン方向にシフトさせるように前記出力特性変更手段（４８）を制御することを特徴とする請求項５に記載の内燃機関の空燃比制御装置。   The output characteristic change control means (38) shifts the inflection point at which the rich / lean output of the upstream sensor (25) is inverted in the lean direction when the flow rate of the EGR gas is higher than a predetermined value. 6. The air-fuel ratio control apparatus for an internal combustion engine according to claim 5, wherein the output characteristic changing means (48) is controlled. 前記内燃機関（１１）の吸気バルブ（２７）と排気バルブ（２８）のうちの少なくとも一方のバルブタイミングを変化させる可変バルブタイミング装置（２９，３０）を備え、
前記出力特性変更制御手段（３８）は、前記バルブタイミングの制御量に応じて前記上流側センサ（２５）の出力特性を変更するように前記出力特性変更手段（４８）を制御することを特徴とする請求項１乃至６のいずれかに記載の内燃機関の空燃比制御装置。 A variable valve timing device (29, 30) for changing the valve timing of at least one of the intake valve (27) and the exhaust valve (28) of the internal combustion engine (11);
The output characteristic change control means (38) controls the output characteristic change means (48) so as to change the output characteristic of the upstream sensor (25) in accordance with the control amount of the valve timing. An air-fuel ratio control apparatus for an internal combustion engine according to any one of claims 1 to 6. 前記出力特性変更制御手段（３８）は、前記バルブタイミングの制御量が所定値よりも大きいときに前記上流側センサ（２５）の出力のリッチ／リーンが反転する変曲点をリーン方向にシフトさせるように前記出力特性変更手段（４８）を制御することを特徴とする請求項７に記載の内燃機関の空燃比制御装置。   The output characteristic change control means (38) shifts the inflection point where the rich / lean output of the upstream sensor (25) is inverted in the lean direction when the control amount of the valve timing is larger than a predetermined value. The air-fuel ratio control apparatus for an internal combustion engine according to claim 7, wherein the output characteristic changing means (48) is controlled as described above. 前記内燃機関（１１）に供給する混合気の空燃比をリーンに制御するリーン燃焼制御を行って前記触媒（２４）の暖機を促進する触媒暖機制御を実行する触媒暖機制御手段（３８）を備え、
前記出力特性変更制御手段（３８）は、前記触媒暖機制御の実行中に前記上流側センサ（２５）の出力のリッチ／リーンが反転する変曲点をリーン方向にシフトさせるように前記出力特性変更手段（４８）を制御することを特徴とする請求項１乃至８のいずれかに記載の内燃機関の空燃比制御装置。 Catalyst warm-up control means (38) for performing catalyst warm-up control for performing warm-up of the catalyst (24) by performing lean combustion control for leanly controlling the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine (11) )
The output characteristic change control means (38) shifts the inflection point at which the rich / lean output of the upstream sensor (25) reverses in the lean direction during execution of the catalyst warm-up control. The air-fuel ratio control apparatus for an internal combustion engine according to any one of claims 1 to 8, wherein the changing means (48) is controlled. 前記出力特性変更制御手段（３８）は、前記触媒（２４）の暖機が完了したとき又は前記内燃機関（１１）の回転変動が所定値以上になったとき又は前記排出ガスの温度が所定値以上になったときに前記上流側センサ（２５）の出力特性を変更していない通常状態に戻すように前記出力特性変更手段（４８）を制御することを特徴とする請求項９に記載の内燃機関の空燃比制御装置。   The output characteristic change control means (38) is configured such that when the warm-up of the catalyst (24) is completed, or when the rotational fluctuation of the internal combustion engine (11) becomes a predetermined value or more, or the temperature of the exhaust gas is a predetermined value. The internal combustion engine according to claim 9, wherein the output characteristic changing means (48) is controlled so as to return the output characteristic of the upstream side sensor (25) to a normal state where the output characteristic has not been changed. Engine air-fuel ratio control device.
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