JP2011149337A - Control diagnostic device for internal combustion engine - Google Patents

Control diagnostic device for internal combustion engine Download PDF

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JP2011149337A
JP2011149337A JP2010011557A JP2010011557A JP2011149337A JP 2011149337 A JP2011149337 A JP 2011149337A JP 2010011557 A JP2010011557 A JP 2010011557A JP 2010011557 A JP2010011557 A JP 2010011557A JP 2011149337 A JP2011149337 A JP 2011149337A
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fuel ratio
air
cylinders
variation
internal combustion
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JP5111529B2 (en
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Yoichi Iiboshi
洋一 飯星
Ryusei Miura
流星 三浦
Eisaku Fukuchi
栄作 福地
Akito Numata
明人 沼田
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Hitachi Astemo Ltd
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Hitachi Automotive Systems Ltd
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Priority to US13/010,302 priority patent/US20110179774A1/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
    • F02D41/008—Controlling each cylinder individually
    • F02D41/0085—Balancing of cylinder outputs, e.g. speed, torque or 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
    • F02D41/1439—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

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Electrical Control Of Air Or Fuel Supplied To Internal-Combustion Engine (AREA)
  • Combined Controls Of Internal Combustion Engines (AREA)

Abstract

<P>PROBLEM TO BE SOLVED: To prevent deterioration of exhaust of an internal combustion engine due to variation in the air-fuel ratio between cylinders, and to specify an abnormal cylinder when the air-fuel ratio of cylinders vary unusually. <P>SOLUTION: A control device for an internal combustion engine includes an upstream air-fuel ratio detector for detecting the upstream air-fuel ratio of a catalyst for controlling emission of exhaust to be discharged from a plurality of cylinders and controls the air-fuel ratio of the plurality of cylinders based on the upstream air-fuel ratio. Variation in the air-fuel ratio between the plurality of cylinders is increased and, at the same time, the upstream air-fuel ratio is controlled to rich. Further, abnormality of variation in the air-fuel ratio between cylinders and an abnormal cylinder are specified based on an estimation value of the air-fuel ratio (the center air-fuel ratio), at which the optimum output of an air-fuel ratio sensor provided downstream of the catalyst or the optimum catalyst emission control efficiency can be obtained, when variation in the air-fuel ratio is increased. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

本発明は、複数気筒を有する内燃機関の制御装置に関する。   The present invention relates to a control device for an internal combustion engine having a plurality of cylinders.

三元触媒を利用した排気浄化システムを備える内燃機関では、排気中のＨＣ，ＣＯ，ＮＯｘの浄化を触媒で行うため、内燃機関で燃焼される混合気の空燃比をＨＣ，ＣＯ，ＮＯｘの三成分を高効率にかつバランスよく浄化できる空燃比（中心空燃比）に制御することが行われる。こうした空燃比の制御は、内燃機関の排気通路に空燃比センサを設け、これによって検出された空燃比を所定の目標空燃比に一致させるフィードバック制御により実現している。   In an internal combustion engine equipped with an exhaust purification system using a three-way catalyst, since the purification of HC, CO, NOx in the exhaust is performed by a catalyst, the air-fuel ratio of the air-fuel mixture combusted in the internal combustion engine is set to three of HC, CO, NOx. Control is performed to an air-fuel ratio (center air-fuel ratio) that can purify components with high efficiency and good balance. Such control of the air-fuel ratio is realized by feedback control in which an air-fuel ratio sensor is provided in the exhaust passage of the internal combustion engine and the air-fuel ratio detected thereby coincides with a predetermined target air-fuel ratio.

特開２００９−３０４５５号公報JP 2009-30455 A

しかしながら、複数気筒を有する内燃機関においては、気筒間空燃比（各気筒ごとの空燃比）がばらつくことが原因で内燃機関の排気性能が悪化するという課題がある。   However, in an internal combustion engine having a plurality of cylinders, there is a problem that exhaust performance of the internal combustion engine deteriorates due to variation in the air-fuel ratio between cylinders (air-fuel ratio for each cylinder).

本発明の目的は、気筒間空燃比ばらつきによる内燃機関の排気性能の悪化を防止することである。   An object of the present invention is to prevent deterioration of exhaust performance of an internal combustion engine due to variation in air-fuel ratio between cylinders.

複数気筒から排出される排気を浄化する触媒と、触媒に流入する排気の空燃比を検出する上流空燃比検出手段と、上流空燃比に基づいて複数気筒の燃料噴射量を制御する空燃比制御手段と、を備えた内燃機関の制御装置において、制御装置は、複数気筒間の空燃比がばらついたときに、上流空燃比を複数気筒間の空燃比がばらつく前の上流空燃比よりリッチになるように複数気筒の燃料噴射量を制御することを特徴とする内燃機関の制御装置である。   Catalyst for purifying exhaust discharged from a plurality of cylinders, upstream air-fuel ratio detection means for detecting the air-fuel ratio of the exhaust flowing into the catalyst, and air-fuel ratio control means for controlling the fuel injection amount of the plurality of cylinders based on the upstream air-fuel ratio When the air-fuel ratio between the plurality of cylinders varies, the control device makes the upstream air-fuel ratio richer than the upstream air-fuel ratio before the air-fuel ratio between the plurality of cylinders varies. The control apparatus for an internal combustion engine controls the fuel injection amount of a plurality of cylinders.

さらに本発明にかかる手段を応用すれば、空燃比ばらつきを積極的に増大させた場合の、触媒下流の空燃比センサ出力あるいは排気三成分（ＨＣ，ＣＯ，ＮＯｘ）と排気中の酸素が過不足なく反応する空燃比（中心空燃比）に基づいて、気筒間空燃比ばらつき異常と異常気筒を特定することもできる。   Furthermore, if the means according to the present invention is applied, the air-fuel ratio sensor output downstream of the catalyst or the exhaust three components (HC, CO, NOx) and the oxygen in the exhaust gas will be excessive or insufficient when the air-fuel ratio variation is positively increased. Based on the air / fuel ratio (central air / fuel ratio) that reacts without any error, it is possible to identify the abnormal variation in air-fuel ratio between cylinders and the abnormal cylinder.

本発明によれば、気筒間空燃比ばらつきによる内燃機関の排気性能の悪化を防止することができる。   According to the present invention, it is possible to prevent deterioration of exhaust performance of an internal combustion engine due to variation in air-fuel ratio between cylinders.

内燃機関の全体構成図。1 is an overall configuration diagram of an internal combustion engine. 気筒間空燃比ばらつきの原理説明図。The principle explanatory drawing of the air-fuel ratio variation between cylinders. 気筒間空燃比ばらつきの影響（空燃比センサ出力と排気）。Influence of air-fuel ratio variation between cylinders (air-fuel ratio sensor output and exhaust). 気筒間空燃比ばらつきの影響（リア酸素センサ出力と排気）。Influence of air-fuel ratio variation between cylinders (rear oxygen sensor output and exhaust). 本発明の制御ブロック図の一例。An example of the control block diagram of this invention. 目標空燃比演算部の一例。An example of a target air fuel ratio calculating part. 目標空燃比および中心空燃比の補正方法の一例。An example of the correction method of a target air fuel ratio and a center air fuel ratio. 空燃比ばらつき度合いと最適浄化空燃比の関係。Relationship between air-fuel ratio variation and optimum purified air-fuel ratio. 本発明を実施したときのタイムチャート（正常時）。The time chart when carrying out the present invention (at the time of normal). 本発明を実施したときのタイムチャート（１番気筒リッチ異常時）。FIG. 3 is a time chart when the present invention is implemented (when the first cylinder is rich). 正常時の中心空燃比変化量。The amount of change in the center air-fuel ratio during normal operation. 正常時のタイムチャート。Normal time chart. １番気筒リッチ異常時の中心空燃比変化量。The amount of change in the center air-fuel ratio when the No. 1 cylinder is rich. １番気筒リッチ異常時のタイムチャート。Time chart when the No. 1 cylinder is rich. １番気筒リーン異常時の中心空燃比変化量。The amount of change in the center air-fuel ratio when the No. 1 cylinder lean is abnormal. １番気筒リーン異常時のタイムチャート。Time chart when the No. 1 cylinder lean is abnormal.

以下本発明の実施形態を、図面を参照して説明する。   Embodiments of the present invention will be described below with reference to the drawings.

図１は、本発明を適用する内燃機関の全体構成図の一例である。ＥＣＵ１０８では、スロットル１０４によって各気筒に流入する空気量を調整し、エンジンヘッド１０６内の各気筒の空燃比が所定値（目標空燃比）となるようにインジェクタ１０５の燃料噴射量を調整する制御が実行される。このインジェクタ１０５の燃料量を決めるために、空気流量センサ１０３で検知する空気量および回転数センサ（図示せず）から検知する回転数などからシリンダ内の空気量を推定して基本となるベース噴射量を決定する。このベース噴射量は、触媒１０７の上流に設置された空燃比センサ１０１が目標とする目標空燃比と一致するように燃料補正が行われる。さらに触媒１０７下流のリア酸素センサ１０２を用いて、触媒において排気三成分（ＨＣ，ＣＯ，ＮＯｘ）と酸素が過不足なく反応する空燃比（中心空燃比）を演算する。そして目標空燃比を中心空燃比近傍に制御することで、空気量の推定値や空燃比センサの出力に多少誤差があっても内燃機関の排気性能は高く維持される。ところが、例えばインジェクタ１０５が劣化して各気筒の噴射量がばらつき、各気筒の空燃比がばらつく異常（気筒間空燃比ばらつき）が生じると、次に説明するようなメカニズムにより排気悪化が生じる。   FIG. 1 is an example of an overall configuration diagram of an internal combustion engine to which the present invention is applied. The ECU 108 performs control to adjust the amount of air flowing into each cylinder by the throttle 104 and adjust the fuel injection amount of the injector 105 so that the air-fuel ratio of each cylinder in the engine head 106 becomes a predetermined value (target air-fuel ratio). Executed. In order to determine the fuel amount of the injector 105, the basic base injection is performed by estimating the air amount in the cylinder from the air amount detected by the air flow sensor 103 and the rotational speed detected from the rotational speed sensor (not shown). Determine the amount. Fuel correction is performed so that the base injection amount matches the target air-fuel ratio targeted by the air-fuel ratio sensor 101 installed upstream of the catalyst 107. Further, the rear oxygen sensor 102 downstream of the catalyst 107 is used to calculate an air-fuel ratio (center air-fuel ratio) at which the exhaust three components (HC, CO, NOx) and oxygen react without excess or deficiency in the catalyst. By controlling the target air-fuel ratio in the vicinity of the central air-fuel ratio, the exhaust performance of the internal combustion engine is maintained high even if there are some errors in the estimated air amount and the output of the air-fuel ratio sensor. However, for example, when the injector 105 deteriorates and the injection amount of each cylinder varies, and an abnormality in which the air-fuel ratio of each cylinder varies (inter-cylinder air-fuel ratio variation) occurs, exhaust deterioration is caused by the mechanism described below.

図２は所定気筒の空燃比をリッチあるいはリーンに意図的にずらし、気筒間の空燃比ばらつきを発生させた際の触媒上流の空燃比センサ出力（測定値）と実際の排気空燃比（真値）の関係を模擬的に示したものである。気筒間の空燃比をばらつかせても空燃比センサ１０１で検知される測定値は目標値一定に制御される。これは前述のように測定値を目標値に保つフィードバック制御が働くためである。しかし、図２に示すように、実際に触媒に流入する排気空燃比は、所定気筒の空燃比がストイキから外れ気筒間の空燃比ばらつきが大きくなるほどリーンになる。言い換えれば、気筒間の空燃比ばらつきにより測定値は真値よりもリッチとなる。なお、ここに示す排気空燃比は触媒上流の排気成分濃度（ＨＣ，ＣＯ，ＣＯ2）などから一般的な方法で計算できる空燃比で、例えば排気分析計の出力として算出されるものである。 FIG. 2 intentionally shifts the air-fuel ratio of a predetermined cylinder to rich or lean, and causes an air-fuel ratio sensor output (measured value) upstream of the catalyst and an actual exhaust air-fuel ratio (true value) when an air-fuel ratio variation occurs between the cylinders. ) In a simulated manner. Even if the air-fuel ratio between cylinders varies, the measured value detected by the air-fuel ratio sensor 101 is controlled to be a target value constant. This is because the feedback control for maintaining the measured value at the target value works as described above. However, as shown in FIG. 2, the exhaust air-fuel ratio that actually flows into the catalyst becomes leaner as the air-fuel ratio of the predetermined cylinder deviates from the stoichiometry and the air-fuel ratio variation between the cylinders increases. In other words, the measured value becomes richer than the true value due to the air-fuel ratio variation between the cylinders. The exhaust air-fuel ratio shown here is an air-fuel ratio that can be calculated by a general method from the exhaust component concentration (HC, CO, CO 2 ) etc. upstream of the catalyst, and is calculated, for example, as the output of an exhaust gas analyzer.

図３に、気筒間空燃比ばらつきにより生じる空燃比センサ１０１出力のリッチずれを確認した実験結果の一例を示す。図３（ａ）は横軸に触媒上流の空燃比センサ出力値、縦軸に排気分析計で計測した触媒下流のＨＣ，ＣＯ，ＮＯｘの測定値を示す。気筒間空燃比ばらつきが無いとＨＣ，ＣＯ，ＮＯｘの中心空燃比は１４.４５である。ところが１番気筒の空燃比を他の３気筒より２０％リッチにすると、この中心空燃比は１４.３５と０.１ほどリッチにシフトしている。すなわち、この実験結果は、気筒間空燃比ばらつきがあると、空燃比制御で空燃比センサ１０１の出力が一定に保たれていても排気空燃比がリーンとなり、ＮＯｘ排出量が増加することを示している。   FIG. 3 shows an example of an experimental result in which a rich shift in the output of the air-fuel ratio sensor 101 caused by the variation in the air-fuel ratio between cylinders is confirmed. In FIG. 3A, the horizontal axis shows the output value of the air-fuel ratio sensor upstream of the catalyst, and the vertical axis shows the measured values of HC, CO, NOx downstream of the catalyst measured by the exhaust gas analyzer. If there is no inter-cylinder air-fuel ratio variation, the central air-fuel ratio of HC, CO, NOx is 14.45. However, if the air-fuel ratio of the first cylinder is made 20% richer than the other three cylinders, the center air-fuel ratio shifts to about 14.35, which is about 0.1. That is, this experimental result indicates that if there is a variation in the air-fuel ratio between cylinders, the exhaust air-fuel ratio becomes lean and the NOx emission amount increases even if the output of the air-fuel ratio sensor 101 is kept constant by air-fuel ratio control. ing.

測定値が真値よりもリッチとなる原因は、空燃比センサ１０１のリッチ応答がリーン応答よりも早いためである。従ってセンサのリッチ応答とリーン応答の差が大きいほどこの現象が顕著となる。その一方で触媒下流に設置されたリア酸素センサ１０２では、この差が小さく、前述のようなリッチシフトは起こらない。   The reason why the measured value becomes richer than the true value is that the rich response of the air-fuel ratio sensor 101 is faster than the lean response. Therefore, this phenomenon becomes more prominent as the difference between the rich response and the lean response of the sensor increases. On the other hand, in the rear oxygen sensor 102 installed downstream of the catalyst, this difference is small and the rich shift as described above does not occur.

図４はリア酸素センサと触媒下流の排気との関係の一例を示す。この実験では１番期気筒の空燃比を他の気筒と同じ（正常）、２０％リッチ，２０％リーンにしている。本実験ではＨＣ，ＣＯ，ＮＯｘをもっとも良く浄化できる時のセンサ出力は気筒間空燃比ばらつきによらず約６００ｍVである。従ってリアＯ2センサ出力の値が約６００ｍＶ一定になるように、空燃比制御の目標空燃比を設定すれば、気筒間空燃比ばらつきによる排気悪化を防止できる。 FIG. 4 shows an example of the relationship between the rear oxygen sensor and the exhaust gas downstream of the catalyst. In this experiment, the air-fuel ratio of the first cylinder is the same (normal) as the other cylinders, 20% rich and 20% lean. In this experiment, the sensor output when HC, CO, and NOx can be best purified is about 600 mV regardless of the variation in the air-fuel ratio between cylinders. Therefore, if the target air-fuel ratio for air-fuel ratio control is set so that the value of the rear O 2 sensor output becomes constant at about 600 mV, exhaust deterioration due to variation in the air-fuel ratio between cylinders can be prevented.

図５から図１０を用いて本発明の第１実施形態について説明する。   A first embodiment of the present invention will be described with reference to FIGS.

図５は本発明を実現する制御ブロック図の一例である。詳細は後述するが、目標空燃比演算部５０１は空燃比センサ出力、空気流量センサ出力から触媒内の酸素貯蔵量（ＯＳ量）を算出し、ＯＳ量が所定範囲に収まるような目標空燃比を演算する。ベース噴射量演算部５０３は空気流量センサ出力およびエンジン回転数センサ（図示せず）出力などからシリンダ空気量を推定し、目標空燃比に基づいてベース噴射量を算出する。空燃比制御演算部５０４は空燃比センサ出力を目標空燃比と一致させるようなベース噴射量の補正値（空燃比補正量）を演算する。そしてＩＮＪ噴射量設定部５０６では気筒毎にベース噴射量に空燃比補正量を反映した燃料パルス幅を設定する。本実施例においては各気筒の気筒ばらつきを実現するため気筒間ばらつき指令値を演算する気筒ばらつき制御演算部５０５、および気筒間のばらつき指令値と触媒下流空燃比センサ出力から気筒ばらつきを判定する気筒ばらつき判定部５０２を備える。ここで設定される気筒ばらつき設定値に応じて目標空燃比をリッチに補正することで、気筒間空燃比ばらつきによる排気悪化を防止できる。さらに気筒間ばらつきをおこなっている際のリア酸素センサ出力に基づいて気筒ばらつき異常を判定できる。   FIG. 5 is an example of a control block diagram for realizing the present invention. Although details will be described later, the target air-fuel ratio calculation unit 501 calculates the oxygen storage amount (OS amount) in the catalyst from the air-fuel ratio sensor output and the air flow rate sensor output, and sets the target air-fuel ratio so that the OS amount falls within a predetermined range. Calculate. A base injection amount calculation unit 503 estimates a cylinder air amount from an air flow rate sensor output and an engine speed sensor (not shown) output, and calculates a base injection amount based on the target air-fuel ratio. The air-fuel ratio control calculation unit 504 calculates a correction value (air-fuel ratio correction amount) of the base injection amount so that the air-fuel ratio sensor output matches the target air-fuel ratio. The INJ injection amount setting unit 506 sets a fuel pulse width reflecting the air-fuel ratio correction amount in the base injection amount for each cylinder. In this embodiment, a cylinder variation control calculation unit 505 that calculates a cylinder variation command value in order to realize cylinder variation of each cylinder, and a cylinder that determines cylinder variation from the cylinder variation command value and the catalyst downstream air-fuel ratio sensor output. A variation determination unit 502 is provided. By correcting the target air-fuel ratio richly in accordance with the cylinder variation set value set here, exhaust deterioration due to variation in the cylinder-to-cylinder air-fuel ratio can be prevented. Further, it is possible to determine the cylinder variation abnormality based on the rear oxygen sensor output when the variation between the cylinders is performed.

図６は目標空燃比演算部の一例を示す。酸素貯蔵量演算部６０２では空燃比センサ出力ＲＡＢＦ，空気流量センサ出力ＱＡおよび中心空燃比ＣＮＴＡＢＦから酸素貯蔵量ＯＳを以下の式１で算出する。   FIG. 6 shows an example of the target air-fuel ratio calculation unit. The oxygen storage amount calculation unit 602 calculates the oxygen storage amount OS from the air-fuel ratio sensor output RABF, the air flow rate sensor output QA, and the central air-fuel ratio CNTABF according to the following formula 1.

ＯＳ＝Σ（ＲＡＢＦ−ＣＮＴＡＢＦ）＊ＱＡ … 数１
目標空燃比補正部６０１では酸素貯蔵量ＯＳが所定範囲からはずれるか、あるいは触媒後ろに設置されたリア酸素センサ出力が所定範囲からはずれた場合に、酸素貯蔵量とリア酸素センサ出力が所定範囲に戻る方向に目標空燃比を変更する。さらに中心空燃比推定部６０３では、酸素貯蔵量が所定範囲内でかつリア酸素センサ出力が所定範囲から外れた場合に中心空燃比を補正する。空燃比補正部６０４では、これら目標空燃比や中心空燃比を気筒空燃比ばらつきに基づいて補正する。 OS = Σ (RABF-CNTABF) * QA
When the oxygen storage amount OS deviates from the predetermined range in the target air-fuel ratio correction unit 601 or the rear oxygen sensor output installed behind the catalyst deviates from the predetermined range, the oxygen storage amount and the rear oxygen sensor output fall within the predetermined range. Change the target air-fuel ratio in the return direction. Further, the central air-fuel ratio estimation unit 603 corrects the central air-fuel ratio when the oxygen storage amount is within a predetermined range and the rear oxygen sensor output is out of the predetermined range. The air-fuel ratio correction unit 604 corrects the target air-fuel ratio and the center air-fuel ratio based on the cylinder air-fuel ratio variation.

図７で目標空燃比および中心空燃比の補正方法の一例を示す。例えば酸素貯蔵量ＯＳが増大した際は目標空燃比をリッチにする。これにより触媒に流入する排気の空燃比がリッチなって酸素貯蔵量が減るため、リア酸素センサでＮＯｘ浄化率の低下を検知するまえにＮＯｘ浄化率の低下を防止できる。また酸素貯蔵量が増大しているのにリア酸素センサ出力がリッチ判定基準を超えた際には、目標空燃比をリッチとするとともに、数１の酸素貯蔵量演算を修正するため、中心空燃比をリッチに補正する。これにより中心空燃比は触媒で排気三成分が酸素と過不足なく反応する空燃比に近づく。   FIG. 7 shows an example of a method for correcting the target air-fuel ratio and the central air-fuel ratio. For example, when the oxygen storage amount OS increases, the target air-fuel ratio is made rich. As a result, the air-fuel ratio of the exhaust gas flowing into the catalyst becomes rich and the oxygen storage amount decreases, so that it is possible to prevent the reduction of the NOx purification rate before the rear oxygen sensor detects the reduction of the NOx purification rate. When the oxygen storage amount increases but the rear oxygen sensor output exceeds the rich criterion, the target air-fuel ratio is made rich and the central air-fuel ratio is corrected in order to correct the oxygen storage amount calculation of equation (1). Is corrected to rich. As a result, the central air-fuel ratio approaches the air-fuel ratio at which the three exhaust components react with oxygen without excess or deficiency in the catalyst.

図８は空燃比のばらつき度合いと最適浄化空燃比の関係を示す。本例では空燃比ばらつきを所定の１気筒の燃料パルス幅を増量させることで実現する。また最適浄化空燃比は、ＨＣ，ＣＯ，ＮＯｘのすべてが触媒で最も高効率で浄化される際に検知された触媒上流の空燃比センサの出力値を表す。本発明では所定気筒の噴射パルス幅を増量すると共に、空燃比制御の目標値をリッチシフトする。特に図的に気筒間空燃比ばらつきを生じさせる場合は、リッチシフト量をあらかじめ実験により求めた最適空燃比より設定することにより、リア酸素センサ出力にもとづいて目標空燃比が最適浄化空燃比まで補正されるよりも早くなり、排気悪化を防止できる。   FIG. 8 shows the relationship between the variation degree of the air-fuel ratio and the optimum purified air-fuel ratio. In this example, the air-fuel ratio variation is realized by increasing the fuel pulse width of a predetermined cylinder. The optimum purified air-fuel ratio represents the output value of the air-fuel ratio sensor upstream of the catalyst detected when all of HC, CO, and NOx are purified with the highest efficiency by the catalyst. In the present invention, the injection pulse width of the predetermined cylinder is increased and the target value of the air-fuel ratio control is richly shifted. In particular, when the air-fuel ratio variation between cylinders is generated graphically, the target air-fuel ratio is corrected to the optimum purified air-fuel ratio based on the rear oxygen sensor output by setting the rich shift amount from the optimum air-fuel ratio obtained in advance through experiments. It is faster than it is done, and exhaust deterioration can be prevented.

図９は本制御を実施した際のタイムチャートの一例である。１番気筒の燃料パルス幅を他の気筒より増量させることで気筒間空燃比ばらつきを開始し、増量を止めることで気筒間ばらつきを終了させている。本実施例では気筒間空燃比ばらつきを開始すると共に目標空燃比をリッチ方向に制御する。この結果、実際の触媒入り口空燃比は触媒の浄化効率が最適となる空燃比を維持しており、リア酸素センサ出力はリッチ判定しきい値とリーン判定しきい値の間に保たれる。一方、気筒間空燃比ばらつきを終了するときは、逆に目標空燃比をリーン方向に制御する。   FIG. 9 is an example of a time chart when this control is performed. The variation in the air-fuel ratio between the cylinders is started by increasing the fuel pulse width of the first cylinder from the other cylinders, and the variation between the cylinders is terminated by stopping the increase. In this embodiment, the air-fuel ratio variation between cylinders is started and the target air-fuel ratio is controlled in the rich direction. As a result, the actual catalyst inlet air-fuel ratio maintains the air-fuel ratio at which the catalyst purification efficiency is optimum, and the rear oxygen sensor output is maintained between the rich determination threshold and the lean determination threshold. On the other hand, when the air-fuel ratio variation between cylinders is finished, the target air-fuel ratio is controlled in the lean direction.

図１０は本制御を気筒間空燃比ばらつき発生時に実施した際のタイムチャートの一例である。この場合、目標空燃比をリッチに制御してもリアＯ2センサ出力がリーン判定を下回っている。これは燃料噴射増量前から１番気筒の空燃比が他の気筒よりもリッチであることを示す。この場合は１気筒ずつ他の気筒も増量してリアＯ2出力がリッチあるいはリーンに外れるかを記録する。１番気筒増量のときリーン、他気筒増量のときリッチになれば、１番気筒がリッチ異常となっていると判定できる。その理由はリッチ気筒をリッチにすると気筒間空燃比ばらつきが想定よりも増加し、あらかじめ実験により求めたリッチ補正が不十分でリア酸素センサ出力がリーンとなるからである。逆にリッチ気筒とバランスさせるためリーンとなっている他の気筒をリッチとすると、想定よりも気筒間空燃比ばらつきが小さくなり、リッチ補正が大きいためリア酸素センサ出力はリッチになる。１番気筒がリーン異常となっている場合はこの逆であり、気筒間空燃比ばらつき制御をすべての気筒で行い、所定の１気筒だけリアＯ2センサ出力がリッチになればその１気筒はリーン異常と判定できる。さらに酸素貯蔵量ＯＳ量が所定範囲から外れた場合には判定を禁止することで、外乱による誤判定を防止できる。なお本制御は触媒が十分活性化した後に実施することが好ましい。 FIG. 10 is an example of a time chart when this control is performed when the variation in air-fuel ratio between cylinders occurs. In this case, the rear O 2 sensor output is below the lean determination even if the target air-fuel ratio is controlled to be rich. This indicates that the air-fuel ratio of the first cylinder is richer than the other cylinders before the fuel injection increase. In this case, the number of other cylinders is increased one by one, and it is recorded whether the rear O 2 output is rich or lean. It can be determined that the No. 1 cylinder is rich abnormal if lean when the No. 1 cylinder is increased and rich when the other cylinder is increased. The reason is that when the rich cylinder is made rich, the variation in the air-fuel ratio between cylinders increases more than expected, and the rich correction obtained by experiments in advance is insufficient and the rear oxygen sensor output becomes lean. Conversely, if other cylinders that are lean to balance with the rich cylinders are made rich, the variation in the air-fuel ratio between the cylinders becomes smaller than expected, and the rich correction is large, so the rear oxygen sensor output becomes rich. The reverse is true when the No. 1 cylinder is in a lean condition, and the inter-cylinder air-fuel ratio variation control is performed for all the cylinders. If the rear O 2 sensor output becomes rich for only one predetermined cylinder, that one cylinder is lean. Can be determined as abnormal. Further, when the oxygen storage amount OS amount is out of the predetermined range, it is possible to prevent erroneous determination due to disturbance by prohibiting the determination. This control is preferably performed after the catalyst has been sufficiently activated.

以上の実施形態を実施すれば以下のような効果を得ることができる。意図的に気筒間空燃比ばらつきを実施したときの排気悪化を防止できる。このため本制御は、空燃比を最適浄化空燃比近傍でチャタリングさせて触媒の浄化効率向上や触媒活性化促進させることができ、排気性能が向上する。さらに気筒間空燃比ばらつきを行った際のリア酸素センサ出力にもとづいて気筒間空燃比ばらつき異常を検知し、かつ空燃比が他と異なる異常気筒を特定できる。   By implementing the above embodiment, the following effects can be obtained. Exhaust deterioration can be prevented when the air-fuel ratio variation between cylinders is intentionally performed. For this reason, in this control, the air-fuel ratio can be chattered in the vicinity of the optimum purified air-fuel ratio to improve the purification efficiency of the catalyst and promote the catalyst activation, thereby improving the exhaust performance. Further, it is possible to detect an abnormal variation in air-fuel ratio between cylinders based on the output of the rear oxygen sensor when the variation in air-fuel ratio between cylinders is performed, and to identify an abnormal cylinder having a different air-fuel ratio.

図１１から図１６を用いて第２実施形態について説明する。第２の実施形態では中心空燃比を用いて異常判定を行う。本実施例では図１１（ａ）に示すように特定の気筒を割合Ｘだけリッチに制御した際に、目標空燃比と中心空燃比をＹ０リッチにシフトする。このＸとＹ０の関係は前述の最適浄化空燃比によって決める。図１１（ｂ）は診断前後での中心空燃比の変化量を示す。正常時では気筒間空燃比がそろう。図１１（ａ）のＡからＢへ中心空燃比を補正しているため中心空燃比の変化量はどの気筒をリッチにしてもＹ０となる。   A second embodiment will be described with reference to FIGS. 11 to 16. In the second embodiment, abnormality determination is performed using the center air-fuel ratio. In this embodiment, as shown in FIG. 11A, when the specific cylinder is controlled to be rich by the ratio X, the target air-fuel ratio and the center air-fuel ratio are shifted to Y0 rich. The relationship between X and Y0 is determined by the optimum purified air-fuel ratio described above. FIG. 11B shows the amount of change in the central air-fuel ratio before and after diagnosis. Under normal conditions, the air-fuel ratio between cylinders is the same. Since the center air-fuel ratio is corrected from A to B in FIG. 11A, the amount of change in the center air-fuel ratio becomes Y0 no matter which cylinder is rich.

図１２に、正常時のタイムチャートを示す。本実施例では診断開始時に１番気筒のみをリッチ割合Ｘ分リッチに制御し、リッチ分Ｘに応じて目標空燃比と中心空燃比をＹ０リッチにする。ここに示すＸとＹ０は図１１（ａ）で説明したように最適浄化空燃比を維持するためのリッチ割合と空燃比リッチシフト量である。この結果、触媒は最適浄化空燃比から外れることなく、触媒下流の空燃比を検知するリアＯ2センサ出力電圧は所定範囲（６００〜８００ｍＶ）の範囲に保たれる。 FIG. 12 shows a time chart in a normal state. In this embodiment, only the first cylinder is controlled to be rich by the rich ratio X at the start of diagnosis, and the target air-fuel ratio and the center air-fuel ratio are made rich by Y0 according to the rich X. X and Y0 shown here are the rich ratio and the air-fuel ratio rich shift amount for maintaining the optimum purified air-fuel ratio as described with reference to FIG. As a result, the catalyst does not deviate from the optimum purified air-fuel ratio, and the rear O 2 sensor output voltage for detecting the air-fuel ratio downstream of the catalyst is maintained within a predetermined range (600 to 800 mV).

次に１気筒がリッチで気筒間空燃比ばらつきが発生している場合について述べる。図１３（ａ）は１気筒がリッチである異常ケースにおける、気筒間空燃比ばらつき制御を実施した際の最適空燃比を示す。Ａｒが気筒ばらつき制御実施前の空燃比であり、Ｘｒｅだけ１番気筒がリッチである。すると他の気筒は空燃比を目標空燃比に保つためにＸｒｅ／（ｎ−１）だけリーンになる。ここでｎは気筒数を表す。リッチ異常である１番気筒をＸだけリッチにした結果がＢｒであり、１番気筒以外の正常気筒をＸだけリッチにした結果がＢｌである。このようにリッチ異常が発生している気筒は想定したＹ０よりもさらにリッチになる。その一方、他の正常気筒をリッチにすると想定したＹ０よりもリーンになる。図１３（ｂ）は各気筒をＸだけリッチにした際の中心空燃比変化量の記録であり、リッチ異常の気筒だけ大きくリッチに中心空燃比が変化する。従って中心空燃比変化量の記録値が図１３（ｂ）のようになれば、中心空燃比異常と判定でき、かつ１気筒だけＹ０よりもリッチになっていることでリッチ異常と判定できる。   Next, the case where one cylinder is rich and the air-fuel ratio variation between cylinders occurs will be described. FIG. 13A shows the optimum air-fuel ratio when the inter-cylinder air-fuel ratio variation control is performed in an abnormal case where one cylinder is rich. Ar is the air-fuel ratio before the cylinder variation control is performed, and the first cylinder is rich by Xre. Then, the other cylinders become lean by Xre / (n-1) in order to keep the air-fuel ratio at the target air-fuel ratio. Here, n represents the number of cylinders. The result of making the rich cylinder No. 1 cylinder rich by X is Br, and the result of making normal cylinders other than the No. 1 cylinder rich by X is Bl. Thus, the cylinder in which the rich abnormality has occurred becomes even richer than the assumed Y0. On the other hand, it becomes leaner than Y0 assumed to make other normal cylinders rich. FIG. 13B is a record of the change amount of the center air-fuel ratio when each cylinder is made rich by X, and the center air-fuel ratio is changed richly and richly only by the cylinder having the rich abnormality. Therefore, if the recorded value of the change amount of the center air-fuel ratio becomes as shown in FIG. 13B, it can be determined that the center air-fuel ratio is abnormal, and it can be determined that the rich abnormality is caused because only one cylinder is richer than Y0.

図１４は１番気筒がリッチ異常であるときのタイムチャートの一例である。１番気筒をＸだけリッチにするとともに、目標空燃比と中心空燃比をリッチに制御する。ところが図１３（ａ）に示すように、このときの最適浄化空燃比はさらにリッチなので、ＮＯｘが浄化できず、それと共に触媒下流のリア酸素センサ出力がリーンとなる。またこの際、酸素貯蔵量は所定範囲から外れていないので、目標空燃比と中心空燃比がリッチに補正される。この補正により、リア酸素センサ出力が所定の範囲一定に収まったときの中心空燃比と診断前の中心空燃比の変化量から異常気筒を特定する。   FIG. 14 is an example of a time chart when the first cylinder is in rich abnormality. The first cylinder is made rich by X, and the target air-fuel ratio and the center air-fuel ratio are controlled to be rich. However, as shown in FIG. 13A, the optimal purified air-fuel ratio at this time is further rich, so NOx cannot be purified, and at the same time, the rear oxygen sensor output downstream of the catalyst becomes lean. At this time, since the oxygen storage amount is not out of the predetermined range, the target air-fuel ratio and the center air-fuel ratio are corrected to be rich. By this correction, an abnormal cylinder is specified from the central air-fuel ratio when the rear oxygen sensor output is kept within a predetermined range and the amount of change in the central air-fuel ratio before diagnosis.

最後に１気筒が他の気筒よりリーンとなる気筒間空燃比ばらつきが発生している場合について述べる。図１５（ａ）は１番気筒がＸｌｅだけ空燃比がリーンになっており、他の気筒はＸｌｅ／（ｎ−１）だけ空燃比がリッチとなっている。最適浄化空燃比はリッチ気筒の空燃比で決まる。Ａｌが診断前の目標空燃比であり、リーン異常気筒をリッチにした結果がＢｌ、残りの正常気筒をリッチにした結果がＢｒである。図１５（ｂ）にも示すようにリーン異常気筒では中心空燃比の変化量が想定したＹ０よりも小さく（リーン）、正常気筒ではＹ０よりもおおきく（リッチ）になっている。この場合も一つだけ傾向が違う、中心空燃比の変化量が少ない１番気筒をリーン異常と判定できる。   Finally, the case where the variation in the air-fuel ratio between cylinders in which one cylinder is leaner than the other cylinders will be described. In FIG. 15A, the air-fuel ratio is lean by Xle in the first cylinder, and the air-fuel ratio is rich by Xle / (n-1) in the other cylinders. The optimum purified air-fuel ratio is determined by the air-fuel ratio of the rich cylinder. Al is the target air-fuel ratio before diagnosis, and the result of making the lean abnormal cylinder rich is Bl, and the result of making the remaining normal cylinders rich is Br. As shown in FIG. 15 (b), the change amount of the center air-fuel ratio is smaller (lean) in the lean abnormal cylinder and larger (rich) in the normal cylinder than Y0. In this case as well, it is possible to determine that the first cylinder having a different tendency and having a small amount of change in the central air-fuel ratio is lean abnormality.

図１６は１番気筒がリーン異常時のタイムチャートを示す。１番気筒の空燃比をＸだけリッチに制御すると共に目標空燃比と中心空燃比をＹ０だけリッチに制御する。この場合は図１５（ａ）に示したように最適浄化空燃比はよりリーンなのでＣＯやＨＣが増加し、触媒下流のリア酸素センサ出力はリッチになる。このため目標空燃比および中心空燃比がリーン補正される。   FIG. 16 shows a time chart when the first cylinder is in a lean abnormality. The air-fuel ratio of the first cylinder is controlled to be rich by X, and the target air-fuel ratio and the central air-fuel ratio are controlled to be rich by Y0. In this case, as shown in FIG. 15 (a), since the optimum purified air-fuel ratio is leaner, CO and HC increase, and the rear oxygen sensor output downstream of the catalyst becomes rich. For this reason, the target air-fuel ratio and the center air-fuel ratio are lean-corrected.

以上の実施形態を実施すれば以下のような効果を得ることができる。所定気筒をリッチに制御し、意図的に気筒空燃比ばらつきを発生させた際の中心空燃比から気筒間空燃比ばらつきの異常気筒を検知できる。なお上流空燃比センサの異常は、どの気筒を増量しても空燃比ばらつき度合いは同じであるため中心空燃比の変化量は殆ど同じになる。このため中心空燃比の変化量をもちいることで本実施例によれば気筒間空燃比ばらつきだけを検知できる。   By implementing the above embodiment, the following effects can be obtained. By controlling the predetermined cylinder to be rich, it is possible to detect an abnormal cylinder having an inter-cylinder air-fuel ratio variation from the center air-fuel ratio when the cylinder air-fuel ratio variation is intentionally generated. The abnormality of the upstream air-fuel ratio sensor is almost the same as the amount of change in the center air-fuel ratio because the degree of air-fuel ratio variation is the same regardless of which cylinder is increased. For this reason, according to the present embodiment, only the variation in the air-fuel ratio between cylinders can be detected by using the change amount of the central air-fuel ratio.

また、気筒間空燃比ばらつきによる上流空燃比検知手段の検知誤差を保障するため、気筒間空燃比を意図的にばらつかせても排気性能が悪化しない。さらに気筒間空燃比がばらついている異常時においては異常検知だけでなく、異常気筒を特定できる。この結果、排気性能のロバスト性が向上すると共に故障時のメンテナンス性も改善できる。   Further, in order to guarantee the detection error of the upstream air-fuel ratio detecting means due to the inter-cylinder air-fuel ratio variation, the exhaust performance does not deteriorate even if the inter-cylinder air-fuel ratio is intentionally varied. Furthermore, when an abnormality occurs in which the air-fuel ratio between cylinders varies, not only abnormality detection but also an abnormal cylinder can be specified. As a result, the robustness of the exhaust performance is improved and the maintainability at the time of failure can be improved.

１０１ 空燃比センサ
１０２ リア酸素センサ
１０３ 空気流量センサ
１０４ スロットル
１０５ インジェクタ
１０６ エンジンヘッド
１０７ 触媒
１０８ ＥＣＵ 101 Air-fuel ratio sensor 102 Rear oxygen sensor 103 Air flow sensor 104 Throttle 105 Injector 106 Engine head 107 Catalyst 108 ECU

Claims (7)

複数気筒から排出される排気を浄化する触媒と、
前記触媒に流入する排気の空燃比を検出する上流空燃比検出手段と、
前記上流空燃比に基づいて前記複数気筒の燃料噴射量を制御する空燃比制御手段と、
を備えた内燃機関の制御装置において、
前記制御装置は、
前記複数気筒間の空燃比がばらついたときに、
前記上流空燃比を前記複数気筒間の空燃比がばらつく前の上流空燃比よりリッチになるように前記複数気筒の燃料噴射量を制御することを特徴とする内燃機関の制御装置。 A catalyst for purifying exhaust discharged from a plurality of cylinders;
Upstream air-fuel ratio detection means for detecting the air-fuel ratio of the exhaust gas flowing into the catalyst;
Air-fuel ratio control means for controlling the fuel injection amount of the plurality of cylinders based on the upstream air-fuel ratio;
An internal combustion engine control apparatus comprising:
The controller is
When the air-fuel ratio among the plurality of cylinders varies,
The control apparatus for an internal combustion engine, wherein the fuel injection amount of the plurality of cylinders is controlled so that the upstream air-fuel ratio becomes richer than an upstream air-fuel ratio before the air-fuel ratio between the plurality of cylinders varies. 前記複数気筒間の空燃比ばらつき度合いに応じて、前記上流空燃比をリッチに制御する度合いを大きくすることを特徴とする請求項１記載の内燃機関の制御装置。   2. The control apparatus for an internal combustion engine according to claim 1, wherein the degree of rich control of the upstream air-fuel ratio is increased in accordance with the degree of air-fuel ratio variation among the plurality of cylinders. 前記内燃機関は、前記触媒から流出する排気の空燃比を検出する下流空燃比検出手段を備え、
前記制御装置は、前記複数気筒間の空燃比がばらついた後の前記下流空燃比に基づいて前記複数気筒間の空燃比ばらつき異常を判定することを特徴とする請求項１〜３記載の内燃機関の制御装置。 The internal combustion engine includes downstream air-fuel ratio detection means for detecting an air-fuel ratio of exhaust flowing out from the catalyst,
The internal combustion engine according to claim 1, wherein the control device determines an abnormality in air-fuel ratio variation among the plurality of cylinders based on the downstream air-fuel ratio after the air-fuel ratio among the plurality of cylinders varies. Control device. 少なくも一つの気筒の燃料噴射量を他の気筒の燃料噴射量よりも所定割合、増量または減量することで前記複数気筒間の空燃比ばらつきを増加させる手段を有することを特徴とする請求項１〜３記載の内燃機関の制御装置。   2. The apparatus according to claim 1, further comprising means for increasing the air-fuel ratio variation among the plurality of cylinders by increasing or decreasing the fuel injection amount of at least one cylinder by a predetermined ratio with respect to the fuel injection amount of the other cylinders. The control device for an internal combustion engine according to any one of claims 1 to 3. 前記複数気筒間の空燃比をばらつかせた後の前記下流空燃比が所定範囲から外れることで、気筒間の空燃比ばらつき異常と判定することを特徴とする請求項４記載の内燃機関の制御装置。   5. The control of an internal combustion engine according to claim 4, wherein the downstream air-fuel ratio after varying the air-fuel ratio among the plurality of cylinders deviates from a predetermined range, thereby determining that the air-fuel ratio variation abnormality among the cylinders is abnormal. apparatus. 少なくとも前記上流空燃比と前記触媒でＨＣ，ＣＯ，ＮＯｘからなる排気三成分と排気中の酸素が過不足なく反応する中心空燃比との差の積算値から前記触媒に貯蔵される酸素貯蔵量を推定し、前記酸素貯蔵量があらかじめ定めた所定範囲になるように前記上流空燃比を制御する内燃機関の制御装置において、前記複数気筒間の空燃比ばらつきに応じて前記中心空燃比をリッチに補正することを特徴とする請求項１〜３記載の内燃機関の制御装置。   The amount of oxygen stored in the catalyst is determined from at least the integrated value of the difference between the upstream air-fuel ratio and the exhaust air three-component composed of HC, CO and NOx and the central air-fuel ratio at which the oxygen in the exhaust reacts without excess or deficiency. In the control apparatus for an internal combustion engine that estimates and controls the upstream air-fuel ratio so that the oxygen storage amount falls within a predetermined range, the central air-fuel ratio is corrected to be rich according to variations in the air-fuel ratio among the plurality of cylinders. The control apparatus for an internal combustion engine according to any one of claims 1 to 3, wherein 特定の１気筒だけ燃料パルス幅を増量あるいは減量して前記気筒間の空燃比ばらつきを増加させ、前記下流空燃比があらかじめ定めた所定範囲よりもリッチになる場合は前記中心空燃比をリッチに補正し、前記下流空燃比があらかじめ定めた所定範囲よりもリーンになる場合には前記中心空燃比をリーンに補正し、前記気筒間の空燃比ばらつきが増加中の中心空燃比の補正量に基づいて前記複数気筒間の空燃比ばらつき異常を判定すること特徴とする請求項６記載の内燃機関の制御装置。   The fuel pulse width is increased or decreased for a specific cylinder to increase the air-fuel ratio variation between the cylinders. When the downstream air-fuel ratio becomes richer than a predetermined range, the center air-fuel ratio is corrected to be rich. When the downstream air-fuel ratio is leaner than a predetermined range, the center air-fuel ratio is corrected to lean, and the variation in the air-fuel ratio between the cylinders is corrected based on the correction amount of the center air-fuel ratio that is increasing. The control apparatus for an internal combustion engine according to claim 6, wherein an abnormality in air-fuel ratio variation among the plurality of cylinders is determined.
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