JP2009127597A - Catalyst degradation diagnostic device - Google Patents

Catalyst degradation diagnostic device Download PDF

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JP2009127597A
JP2009127597A JP2007306443A JP2007306443A JP2009127597A JP 2009127597 A JP2009127597 A JP 2009127597A JP 2007306443 A JP2007306443 A JP 2007306443A JP 2007306443 A JP2007306443 A JP 2007306443A JP 2009127597 A JP2009127597 A JP 2009127597A
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catalyst
air
fuel ratio
fuel
deterioration
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Koichi Kimura
光壱 木村
Toru Kidokoro
徹 木所
Yutaka Sawada
裕 澤田
Yasushi Iwasaki
靖志 岩▲崎▼
Koichi Kitaura
浩一 北浦
Hiroshi Miyamoto
寛史 宮本
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Toyota Motor Corp
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Toyota Motor Corp
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Abstract

<P>PROBLEM TO BE SOLVED: To provide a catalyst degradation diagnostic device capable of detecting the deterioration of a catalyst with a higher degree of accuracy. <P>SOLUTION: This catalyst degradation diagnostic device for an internal combustion engine diagnoses the deterioration of the catalyst arranged in an exhaust passage of the internal combustion engine. The device is configured to discriminate the concentration of sulfur in fuel based on the difference between the rich side maximum value of an output value of an oxygen sensor in the downstream of the catalyst and a steady value obtained when the value drops off from this maximum value to a lean side and comes into almost steady state, thereby determining the deterioration of the catalyst while taking the discrimination result into consideration. This constitution can detect the deterioration of the catalyst with the higher degree of accuracy since the deterioration is determined while taking into consideration an influence of the sulfur. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

本発明は、触媒劣化診断装置に関する。   The present invention relates to a catalyst deterioration diagnosis apparatus.

例えば、車両用の内燃機関において、その排気系には排気ガスを浄化するための触媒が設置されている。この触媒の中には酸素吸蔵能(O2ストレージ能)を有するものがあり、これは、触媒に流入する排気ガスの空燃比が理論空燃比(ストイキ)よりも大きくなると、即ちリーンになると排気ガス中に存在する過剰酸素を吸着保持し、触媒流入排気ガスの空燃比がストイキよりも小さくなると、即ちリッチになると吸着保持された酸素を放出する。例えばガソリンエンジンでは触媒に流入する排気ガスがストイキ近傍となるよう空燃比制御が行われるが、酸素吸蔵能を有する三元触媒を使用すると、運転条件により実際の空燃比がストイキから多少振れてしまっても、三元触媒による酸素の吸蔵・放出作用により、そのような空燃比ずれを吸収することができる。 For example, in an internal combustion engine for a vehicle, a catalyst for purifying exhaust gas is installed in the exhaust system. Some of these catalysts have an oxygen storage capacity (O 2 storage capacity). This is because when the air-fuel ratio of the exhaust gas flowing into the catalyst becomes larger than the stoichiometric air-fuel ratio (stoichiometric), that is, the exhaust gas becomes lean. Excess oxygen present in the gas is adsorbed and held, and when the air-fuel ratio of the catalyst inflow exhaust gas becomes smaller than the stoichiometric, that is, becomes rich, the adsorbed and held oxygen is released. For example, in a gasoline engine, air-fuel ratio control is performed so that the exhaust gas flowing into the catalyst is in the vicinity of the stoichiometric. However, such an air-fuel ratio shift can be absorbed by the oxygen storage / release action of the three-way catalyst.

触媒が劣化すると触媒の浄化効率が低下する。触媒の劣化度と酸素吸蔵能の低下度との間にはともに貴金属を介する反応であるため相関関係がある。よって、酸素吸蔵能が低下したことを検出することで触媒が劣化したことを検出することができる。一般的には、触媒に流入する排気ガスの空燃比を強制的にリッチ及びリーンに切り替えるアクティブ空燃比制御を行い、このアクティブ空燃比制御の実行に伴って触媒の酸素吸蔵容量を計測し、計測した酸素吸蔵容量に基づいて触媒の劣化を診断するいわゆるCmax法が採用される。
酸素吸蔵容量の計測においては、例えば、特許文献1,2等に開示されているように、硫黄濃度が高い燃料の場合、硫黄被毒により、触媒が一時的に劣化し、計測される酸素吸蔵容量が低下することが知られている。
When the catalyst deteriorates, the purification efficiency of the catalyst decreases. There is a correlation between the degree of deterioration of the catalyst and the degree of reduction of the oxygen storage capacity because they are reactions through noble metals. Therefore, it is possible to detect that the catalyst has deteriorated by detecting that the oxygen storage capacity has decreased. In general, active air-fuel ratio control that forcibly switches the air-fuel ratio of exhaust gas flowing into the catalyst to rich and lean is performed, and the oxygen storage capacity of the catalyst is measured and measured along with the execution of this active air-fuel ratio control. A so-called Cmax method for diagnosing deterioration of the catalyst based on the oxygen storage capacity is employed.
In the measurement of the oxygen storage capacity, for example, in the case of a fuel having a high sulfur concentration, as disclosed in Patent Documents 1 and 2, the catalyst is temporarily deteriorated due to sulfur poisoning, and the measured oxygen storage capacity is measured. It is known that capacity decreases.

特開2006−291773号公報JP 2006-291773 A 特開2003−83145号公報JP 2003-83145 A

燃料中の硫黄が一時的に触媒の表面に吸着されると、これが触媒の酸素吸放出反応を阻害し、あたかも熱劣化により触媒の貴金属がシンタリングしたような判定結果と同様の判定結果が生じ、触媒の劣化が熱劣化によるものと誤って判定してしまう可能性があった。   When sulfur in the fuel is temporarily adsorbed on the surface of the catalyst, this hinders the oxygen absorption and release reaction of the catalyst, resulting in the same determination result as if the noble metal of the catalyst was sintered due to thermal degradation. There is a possibility that the deterioration of the catalyst is erroneously determined to be due to thermal deterioration.

本発明は、上記の事情に鑑みて成されたものであり、その目的とするところは、より精度の高い触媒の劣化検出が可能な触媒劣化診断装置を提供することにある。   The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a catalyst deterioration diagnosis apparatus capable of detecting deterioration of a catalyst with higher accuracy.

本発明に係る触媒劣化診断装置は、内燃機関の排気通路に配置された触媒の劣化を診断する内燃機関の触媒劣化診断装置であって、燃料中の硫黄濃度を判別する硫黄濃度判別手段と、前記硫黄濃度判別手段の判別結果を考慮して触媒劣化を判断する触媒劣化判断手段と、を有し、前記硫黄濃度判別手段は、触媒上流の空燃比をアクティブ制御によりリッチからリーンに切り替えたときの、触媒下流の酸素センサの出力値のリッチ側最大値と、このリッチ側最大値からリーン側へ値が落ち込んでほぼ定常状態となったときの定常値との差に基づいて、燃料中の硫黄濃度を判別する、ことを特徴とする。   A catalyst deterioration diagnosis device according to the present invention is a catalyst deterioration diagnosis device for an internal combustion engine for diagnosing deterioration of a catalyst disposed in an exhaust passage of the internal combustion engine, and a sulfur concentration determination means for determining a sulfur concentration in fuel, Catalyst deterioration determining means for determining catalyst deterioration in consideration of the determination result of the sulfur concentration determining means, and the sulfur concentration determining means when the air-fuel ratio upstream of the catalyst is switched from rich to lean by active control. Based on the difference between the rich side maximum value of the output value of the oxygen sensor downstream of the catalyst and the steady state value when the value drops from the rich side maximum value to the lean side and becomes almost steady state. The sulfur concentration is discriminated.

上記構成において、前記硫黄濃度判別手段は、燃料中の硫黄濃度を判別する際に、前記リッチ側最大値と定常値との差に加えて、前記触媒下流の酸素センサの出力波形形状が高硫黄燃料特有の形状をとるか否かを判断する、構成を採用できる。   In the above configuration, when the sulfur concentration determination means determines the sulfur concentration in the fuel, in addition to the difference between the maximum value on the rich side and the steady value, the output waveform shape of the oxygen sensor downstream of the catalyst is high sulfur. It is possible to adopt a configuration for determining whether or not a fuel-specific shape is taken.

上記構成において、前記触媒劣化判断手段は、触媒上流空燃比のアクティブ制御時の触媒の酸素吸蔵容量に基いて触媒劣化を判断し、前記硫黄濃度判別手段の判別結果に応じて、触媒劣化判断に用いる酸素吸蔵容量または触媒劣化を判断するための判定値を補正する、構成を採用できる。   In the above configuration, the catalyst deterioration determination means determines the catalyst deterioration based on the oxygen storage capacity of the catalyst during active control of the catalyst upstream air-fuel ratio, and determines the catalyst deterioration based on the determination result of the sulfur concentration determination means. A configuration that corrects a determination value for determining the oxygen storage capacity or catalyst deterioration to be used can be adopted.

本発明によれば、硫黄の影響を考慮して触媒劣化を判断するので、より精度の高い触媒の劣化検出が可能となる。   According to the present invention, the catalyst deterioration is determined in consideration of the influence of sulfur, so that it is possible to detect the deterioration of the catalyst with higher accuracy.

以下、本発明の最良の実施形態について、添付図面を参照しつつ説明する。
図1は、本実施形態の構成を示す概略図である。図示されるように、内燃機関1は、シリンダブロック2に形成された燃焼室3の内部で燃料および空気の混合気を燃焼させ、燃焼室3内でピストン4を往復移動させることにより動力を発生する。内燃機関1は車両に搭載された多気筒エンジン(1気筒のみ図示)であり、火花点火式内燃機関、より具体的にはガソリンエンジンである。
DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, exemplary embodiments of the invention will be described with reference to the accompanying drawings.
FIG. 1 is a schematic diagram showing the configuration of the present embodiment. As shown in the figure, the internal combustion engine 1 generates power by burning a mixture of fuel and air inside a combustion chamber 3 formed in a cylinder block 2 and reciprocating a piston 4 in the combustion chamber 3. To do. The internal combustion engine 1 is a multi-cylinder engine (only one cylinder is shown) mounted on a vehicle, and is a spark ignition type internal combustion engine, more specifically, a gasoline engine.

内燃機関1のシリンダヘッドには、吸気ポートを開閉する吸気弁Viと、排気ポートを開閉する排気弁Veとが気筒ごとに配設されている。各吸気弁Viおよび各排気弁Veは図示しないカムシャフトによって開閉させられる。また、シリンダヘッドの頂部には、燃焼室3内の混合気に点火するための点火プラグ7が気筒ごとに取り付けられている。   In the cylinder head of the internal combustion engine 1, an intake valve Vi for opening and closing the intake port and an exhaust valve Ve for opening and closing the exhaust port are provided for each cylinder. Each intake valve Vi and each exhaust valve Ve are opened and closed by a camshaft (not shown). A spark plug 7 for igniting the air-fuel mixture in the combustion chamber 3 is attached to the top of the cylinder head for each cylinder.

各気筒の吸気ポートは気筒毎の枝管を介して吸気集合室であるサージタンク8に接続されている。サージタンク8の上流側には吸気集合通路をなす吸気管13が接続されており、吸気管13の上流端にはエアクリーナ9が設けられている。そして吸気管13には、上流側から順に、吸入空気量を検出するためのエアフローメータ5と、電子制御式スロットルバルブ10とが組み込まれている。なお吸気ポート、サージタンク8及び吸気管13により吸気通路が形成される。   The intake port of each cylinder is connected to a surge tank 8 serving as an intake air collecting chamber via a branch pipe for each cylinder. An intake pipe 13 that forms an intake manifold passage is connected to the upstream side of the surge tank 8, and an air cleaner 9 is provided at the upstream end of the intake pipe 13. An air flow meter 5 for detecting the intake air amount and an electronically controlled throttle valve 10 are incorporated in the intake pipe 13 in order from the upstream side. An intake passage is formed by the intake port, the surge tank 8 and the intake pipe 13.

吸気通路、特に吸気ポート内に燃料を噴射するインジェクタ(燃料噴射弁)12が気筒ごとに配設される。インジェクタ12から噴射された燃料は吸入空気と混合されて混合気をなし、この混合気が吸気弁Viの開弁時に燃焼室3に吸入され、ピストン4で圧縮され、点火プラグ7で点火燃焼させられる。   An injector (fuel injection valve) 12 that injects fuel into the intake passage, particularly into the intake port, is provided for each cylinder. The fuel injected from the injector 12 is mixed with intake air to form an air-fuel mixture. The air-fuel mixture is sucked into the combustion chamber 3 when the intake valve Vi is opened, compressed by the piston 4, and ignited and burned by the spark plug 7. It is done.

一方、各気筒の排気ポートは気筒毎の枝管を介して排気集合通路をなす排気管6に接続されており、排気管6には、O2ストレージ機能(酸素吸蔵能)を有する三元触媒からなる触媒11が取り付けられている。なお排気ポート、枝管及び排気管6により排気通路が形成される。触媒11の上流側と下流側とにそれぞれ、排気中の酸素濃度に基づいて排気空燃比を検出する空燃比センサ17及びO2(酸素)センサ18が設置されている。空燃比センサ17は所謂広域空燃比センサからなり、比較的広範囲に亘る空燃比を連続的に検出可能で、排気空燃比に比例した値の信号を出力する。他方、O2センサ18は、理論空燃比を境に出力値が急変する特性を持つ。 On the other hand, the exhaust port of each cylinder is connected to an exhaust pipe 6 forming an exhaust collecting passage through a branch pipe for each cylinder, and the exhaust pipe 6 has a three-way catalyst having an O 2 storage function (oxygen storage capacity). A catalyst 11 comprising: An exhaust passage is formed by the exhaust port, the branch pipe, and the exhaust pipe 6. An air-fuel ratio sensor 17 and an O 2 (oxygen) sensor 18 that detect the exhaust air-fuel ratio based on the oxygen concentration in the exhaust gas are installed on the upstream side and the downstream side of the catalyst 11, respectively. The air-fuel ratio sensor 17 is a so-called wide-area air-fuel ratio sensor, can continuously detect an air-fuel ratio over a relatively wide range, and outputs a signal having a value proportional to the exhaust air-fuel ratio. On the other hand, the O 2 sensor 18 has a characteristic that its output value changes abruptly at the theoretical air-fuel ratio.

上述の点火プラグ7、スロットルバルブ10及びインジェクタ12等は、制御手段としての電子制御ユニット(以下ECUと称す)20に電気的に接続されている。ECU20は、何れも図示されないCPU、ROM、RAM、入出力ポート、および記憶装置等を含むものである。またECU20には、図示されるように、前述のエアフローメータ5、空燃比センサ17、O2センサ18のほか、内燃機関1のクランク角を検出するクランク角センサ14、アクセル開度を検出するアクセル開度センサ15、その他の各種センサが図示されないA/D変換器等を介して電気的に接続されている。ECU20は、各種センサの検出値等に基づいて、所望の出力が得られるように、点火プラグ7、スロットルバルブ10、インジェクタ12等を制御し、点火時期、燃料噴射量、燃料噴射時期、スロット
ル開度等を制御する。
The spark plug 7, the throttle valve 10, the injector 12, and the like described above are electrically connected to an electronic control unit (hereinafter referred to as ECU) 20 as a control means. The ECU 20 includes a CPU, a ROM, a RAM, an input / output port, a storage device, and the like, all not shown. In addition to the air flow meter 5, air-fuel ratio sensor 17, and O 2 sensor 18, the ECU 20 includes a crank angle sensor 14 that detects the crank angle of the internal combustion engine 1 and an accelerator that detects the accelerator opening, as shown in the figure. The opening sensor 15 and other various sensors are electrically connected via an A / D converter or the like (not shown). The ECU 20 controls the ignition plug 7, the throttle valve 10, the injector 12, etc. so as to obtain a desired output based on the detection values of various sensors, etc., and performs ignition timing, fuel injection amount, fuel injection timing, throttle opening. Control the degree etc.

触媒11は、これに流入する排気ガスの空燃比A/Fが理論空燃比(ストイキ、例えば、A/Fs=14.6)近傍のときにNOx ,HCおよびCOを同時に浄化する。そしてこれに対応して、ECU20は、内燃機関の通常運転時、触媒11に流入する排気ガスの空燃比即ち触媒前空燃比A/Ffrが理論空燃比に一致するように空燃比を制御する。具体的にはECU20は、理論空燃比に等しい目標空燃比A/Ftを設定すると共に、空燃比センサ17により検出された触媒前空燃比A/Ffrが目標空燃比A/Ftに一致するように、インジェクタ12から噴射される燃料噴射量をフィードバック制御する。これにより触媒11に流入する排気ガスの空燃比は理論空燃比近傍に保たれ、触媒11において最大の浄化性能が発揮されるようになる。   The catalyst 11 simultaneously purifies NOx, HC, and CO when the air-fuel ratio A / F of the exhaust gas flowing into the catalyst 11 is near the stoichiometric air-fuel ratio (stoichiometric, for example, A / Fs = 14.6). Correspondingly, during normal operation of the internal combustion engine, the ECU 20 controls the air-fuel ratio so that the air-fuel ratio of the exhaust gas flowing into the catalyst 11, that is, the pre-catalyst air-fuel ratio A / Ffr, matches the stoichiometric air-fuel ratio. Specifically, the ECU 20 sets a target air-fuel ratio A / Ft equal to the stoichiometric air-fuel ratio, and the pre-catalyst air-fuel ratio A / Ffr detected by the air-fuel ratio sensor 17 matches the target air-fuel ratio A / Ft. The fuel injection amount injected from the injector 12 is feedback-controlled. As a result, the air-fuel ratio of the exhaust gas flowing into the catalyst 11 is kept in the vicinity of the theoretical air-fuel ratio, and the maximum purification performance is exhibited in the catalyst 11.

ここで、触媒11についてより詳細に説明する。図2に示すように、触媒11においては、図示しない担体基材の表面上にコート材31が被覆され、このコート材31に微粒子状の触媒成分32が多数分散配置された状態で保持され、触媒11内部で露出されている。触媒成分32は主にPt,Pd等の貴金属からなり、NOx ,HCおよびCOといった排ガス成分を反応させる際の活性点となる。他方、コート材31は、排気ガスと触媒成分32との界面における反応を促進させる助触媒の役割を担うと共に、雰囲気ガスの空燃比に応じて酸素を吸収放出可能な酸素吸蔵成分を含む。酸素吸蔵成分は例えば酸化セリウムCeO2やジルコニアからなる。例えば、触媒成分32及びコート材31の雰囲気ガスが理論空燃比よりリッチであると、触媒成分32の周囲に存在する酸素吸蔵成分に吸蔵さ
れていた酸素が放出され、この結果、放出された酸素によりHCおよびCOといった未燃成分が酸化され、浄化される。逆に、触媒成分32及びコート材31の雰囲気ガスが理論空燃比よりリーンであると、触媒成分32の周囲に存在する酸素吸蔵成分が雰囲気ガスから酸素を吸収し、この結果NOxが還元浄化される。
Here, the catalyst 11 will be described in more detail. As shown in FIG. 2, in the catalyst 11, a coating material 31 is coated on the surface of a carrier base material (not shown), and the coating material 31 is held in a state in which a large number of particulate catalyst components 32 are dispersedly arranged. The catalyst 11 is exposed inside. The catalyst component 32 is mainly composed of a noble metal such as Pt or Pd, and serves as an active point for reacting exhaust gas components such as NOx, HC and CO. On the other hand, the coating material 31 plays the role of a promoter that promotes the reaction at the interface between the exhaust gas and the catalyst component 32 and includes an oxygen storage component capable of absorbing and releasing oxygen according to the air-fuel ratio of the atmospheric gas. The oxygen storage component is made of, for example, cerium oxide CeO 2 or zirconia. For example, if the atmosphere gas of the catalyst component 32 and the coating material 31 is richer than the stoichiometric air-fuel ratio, the oxygen stored in the oxygen storage component present around the catalyst component 32 is released, and as a result, the released oxygen As a result, unburned components such as HC and CO are oxidized and purified. On the contrary, when the atmosphere gas of the catalyst component 32 and the coating material 31 is leaner than the stoichiometric air-fuel ratio, the oxygen storage component present around the catalyst component 32 absorbs oxygen from the atmosphere gas, and as a result, NOx is reduced and purified. The

このような酸素吸放出作用により、通常の空燃比制御の際に触媒前空燃比A/Ffrが理論空燃比に対し多少ばらついたとしても、NOx、HCおよびCOといった三つの排気ガス成分を同時浄化することができる。よって通常の空燃比制御において、触媒前空燃比A/Ffrを敢えて理論空燃比を中心に微小振動させ、酸素の吸放出を繰り返させることにより排ガス浄化を行うことも可能である。   By such an oxygen absorption / release action, even if the pre-catalyst air-fuel ratio A / Ffr slightly varies from the stoichiometric air-fuel ratio during normal air-fuel ratio control, three exhaust gas components such as NOx, HC and CO are simultaneously purified. can do. Therefore, in normal air-fuel ratio control, it is also possible to purify the exhaust gas by making the pre-catalyst air-fuel ratio A / Ffr oscillate minutely around the theoretical air-fuel ratio and repeating the absorption and release of oxygen.

ところで、新品状態の触媒11では前述したように細かい粒子状の触媒成分32が多数均等に分散配置されており、排気ガスと触媒成分32との接触確率が高い状態に維持されている。しかしながら、触媒11が劣化してくると、一部の触媒成分32に消失が見られるほか、触媒成分32同士が排気熱で焼き固まって焼結状態になるものがある(図の破線参照)。こうなると排気ガスと触媒成分32との接触確率の低下を引き起こし、浄化率を落としめる原因となる。そしてこのほかに、触媒成分32の周囲に存在するコート材31の量、即ち酸素吸蔵成分の量が減少し、酸素吸蔵能自体が低下する。   By the way, in the catalyst 11 in the new state, as described above, a large number of fine particulate catalyst components 32 are uniformly distributed, and the contact probability between the exhaust gas and the catalyst component 32 is kept high. However, when the catalyst 11 deteriorates, some of the catalyst components 32 are lost, and some of the catalyst components 32 are baked and solidified by exhaust heat (see broken lines in the figure). In this case, the contact probability between the exhaust gas and the catalyst component 32 is lowered, and the purification rate is lowered. In addition to this, the amount of the coating material 31 existing around the catalyst component 32, that is, the amount of the oxygen storage component decreases, and the oxygen storage capacity itself decreases.

このように、触媒11の劣化度と触媒11の持つ酸素吸蔵能の低下度とは相関関係にある。そこで本実施形態では、触媒11の酸素吸蔵能を検出することにより触媒11の劣化度を検出することとしている。ここで、触媒11の酸素吸蔵能は、現状の触媒11が吸蔵し得る最大酸素量である酸素吸蔵容量(OSC;O2 Strage Capacity、単位はg)の大きさによって表される。 Thus, the degree of deterioration of the catalyst 11 and the degree of decrease in the oxygen storage capacity of the catalyst 11 are in a correlation. Therefore, in this embodiment, the degree of deterioration of the catalyst 11 is detected by detecting the oxygen storage capacity of the catalyst 11. Here, the oxygen storage capacity of the catalyst 11 is represented by the size of the oxygen storage capacity (OSC; O 2 Strage Capacity, the unit is g), which is the maximum amount of oxygen that the current catalyst 11 can store.

以下、触媒劣化診断について説明する。
触媒劣化診断は、前述のCmax法によるものを基本とする。そして触媒11の劣化診断に際しては、ECU20によりアクティブ空燃比制御が実行される。アクティブ空燃比制御において、触媒前空燃比A/Ffrは、所定の中心空燃比A/Fcを境にリッチ側及びリーン側に強制的に(アクティブに)交互に切り替えられる。なおリッチ側に変化されたときの空燃比をリッチ空燃比A/Fr、リーン側に変化されたときの空燃比をリーン空燃比A/Flと称す。このアクティブ空燃比制御によって触媒前空燃比A/Ffrがリッチ側又はリーン側に変化されているときに触媒の酸素吸蔵容量OSCが計測される。
Hereinafter, the catalyst deterioration diagnosis will be described.
The catalyst deterioration diagnosis is based on the above-described Cmax method. When the deterioration diagnosis of the catalyst 11 is performed, the active air-fuel ratio control is executed by the ECU 20. In the active air-fuel ratio control, the pre-catalyst air-fuel ratio A / Ffr is forcibly (actively) alternately switched to the rich side and the lean side with a predetermined center air-fuel ratio A / Fc as a boundary. The air-fuel ratio when changed to the rich side is referred to as rich air-fuel ratio A / Fr, and the air-fuel ratio when changed to the lean side is referred to as lean air-fuel ratio A / Fl. When the pre-catalyst air-fuel ratio A / Ffr is changed to the rich side or the lean side by this active air-fuel ratio control, the oxygen storage capacity OSC of the catalyst is measured.

触媒11の劣化診断は、内燃機関1の定常運転時で且つ触媒11が活性温度域にあるときに実行される。触媒11の温度(触媒床温)の計測については、温度センサを用いて直接検出してもよいが、本実施形態の場合内燃機関の運転状態から推定することとしている。例えばECU20は、エアフローメータ5によって検出される吸入空気量Gaと、クランク角センサ14の出力に基づいて検出される機関回転速度Ne(rpm)とに基づいて、予め実験等を通じて設定されたマップ又は関数を利用し、触媒11の温度を推定する。   The deterioration diagnosis of the catalyst 11 is executed during steady operation of the internal combustion engine 1 and when the catalyst 11 is in the active temperature range. Measurement of the temperature of the catalyst 11 (catalyst bed temperature) may be detected directly using a temperature sensor, but in the present embodiment, it is estimated from the operating state of the internal combustion engine. For example, the ECU 20 uses a map or a map set in advance through experiments or the like based on the intake air amount Ga detected by the air flow meter 5 and the engine rotational speed Ne (rpm) detected based on the output of the crank angle sensor 14. The temperature of the catalyst 11 is estimated using the function.

図3(A),(B)にはそれぞれ、アクティブ空燃比制御実行時における空燃比センサ17及びOセンサ18の出力が実線で示されている。また、図3(A)には、ECU20内部で発生される目標空燃比A/Ftが破線で示されている。空燃比センサ17及びOセンサ18の出力値はそれぞれ触媒前空燃比A/Ffr及び触媒後空燃比A/Frrの値に対応する。 In FIGS. 3A and 3B, the outputs of the air-fuel ratio sensor 17 and the O 2 sensor 18 when the active air-fuel ratio control is executed are indicated by solid lines. In FIG. 3A, the target air-fuel ratio A / Ft generated inside the ECU 20 is indicated by a broken line. The output values of the air-fuel ratio sensor 17 and the O 2 sensor 18 correspond to the values of the pre-catalyst air-fuel ratio A / Ffr and the post-catalyst air-fuel ratio A / Frr, respectively.

図3(A)に示されるように、目標空燃比A/Ftは、中心空燃比A/Fcを中心として、そこからリッチ側に所定の振幅(リッチ振幅Ar、Ar>0)だけ離れた空燃比(リッチ空燃比A/Fr)と、そこからリーン側に所定の振幅(リーン振幅Al、Al>0)だけ離れた空燃比(リーン空燃比A/Fl)とに強制的に、且つ交互に切り替えられる。そしてこの目標空燃比A/Ftの切り替えに追従して、実際値としての触媒前空燃比A/Ffrも、目標空燃比A/Ftに対し僅かな時間遅れを伴って切り替わる。このことから目標空燃比A/Ftと触媒前空燃比A/Ffrとは時間遅れがあること以外等価であることが理解されよう。   As shown in FIG. 3 (A), the target air-fuel ratio A / Ft is an air that is separated from the center air-fuel ratio A / Fc by a predetermined amplitude (rich amplitude Ar, Ar> 0) on the rich side. Forcibly and alternately between the fuel ratio (rich air-fuel ratio A / Fr) and the air-fuel ratio (lean air-fuel ratio A / Fl) that is away from it by a predetermined amplitude (lean amplitude Al, Al> 0). Can be switched. Following the switching of the target air-fuel ratio A / Ft, the pre-catalyst air-fuel ratio A / Ffr as an actual value is also switched with a slight time delay with respect to the target air-fuel ratio A / Ft. From this, it will be understood that the target air-fuel ratio A / Ft and the pre-catalyst air-fuel ratio A / Ffr are equivalent except that there is a time delay.

図示例においてリッチ振幅Arとリーン振幅Alとは等しい。例えば中心空燃比A/Fc=14.6、リッチ空燃比A/Fr=14.1、リーン空燃比A/Fl=15.1、リッチ振幅Ar=リーン振幅Al=0.5である。通常の空燃比制御の場合に比べ、アクティブ空燃比制御の場合は空燃比の振り幅が大きく、即ちリッチ振幅Arとリーン振幅Alとの値は大きい。   In the illustrated example, the rich amplitude Ar and the lean amplitude Al are equal. For example, the center air-fuel ratio A / Fc = 14.6, the rich air-fuel ratio A / Fr = 14.1, the lean air-fuel ratio A / Fl = 15.1, the rich amplitude Ar = the lean amplitude Al = 0.5. Compared with the normal air-fuel ratio control, the active air-fuel ratio control has a larger amplitude of the air-fuel ratio, that is, the values of the rich amplitude Ar and the lean amplitude Al are larger.

目標空燃比A/Ftがリッチとリーンとで切り替えられるタイミングは、Oセンサ18の出力に基づいて決定される。具体的には、図3(B)に図示したように、触媒後空燃比A/Frrがリッチ側からリーン側に変化し、Oセンサ18の出力がリーン判定値VLと等しくなる時点(t1,t3等)で、目標空燃比A/Ftはリーン空燃比A/Flからリッチ空燃比A/Frに切り替えられる。触媒後空燃比A/Frrがリーン側からリッチ側に変化し、Oセンサ18の出力がリッチ判定値VRとなる時点(t2等)で目標空燃比A/Ftはリッチ空燃比A/Frからリーン空燃比A/Flに切り替えられる。尚、VR>VLであり、例えばVR=0.59(V)、VL=0.21(V)である。 The timing at which the target air-fuel ratio A / Ft is switched between rich and lean is determined based on the output of the O 2 sensor 18. Specifically, as shown in FIG. 3B, the post-catalyst air-fuel ratio A / Frr changes from the rich side to the lean side, and the output of the O 2 sensor 18 becomes equal to the lean determination value VL (t1 , T3, etc.), the target air-fuel ratio A / Ft is switched from the lean air-fuel ratio A / Fl to the rich air-fuel ratio A / Fr. When the post-catalyst air-fuel ratio A / Frr changes from the lean side to the rich side, and the output of the O 2 sensor 18 reaches the rich determination value VR (such as t2), the target air-fuel ratio A / Ft is changed from the rich air-fuel ratio A / Fr. The lean air-fuel ratio A / Fl is switched. Note that VR> VL, for example, VR = 0.59 (V) and VL = 0.21 (V).

このような空燃比変化を行うアクティブ空燃比制御を実行しつつ、次のようにして触媒11の酸素吸蔵容量OSCが計測され、触媒11の劣化が判定される。
図3に示す時刻t1より前では目標空燃比A/Ftがリーン空燃比A/Flとされ、触媒11にはリーンガスが流入されている。このとき触媒11では酸素を吸収し続けているが、一杯に酸素を吸収した時点でそれ以上酸素を吸収できなくなり、リーンガスが触媒11を通り抜けて触媒11の下流側に流れ出す。こうなると触媒後空燃比A/Frrがリーン側に変化し、Oセンサ18の出力電圧がリーン判定値VLに達した時点(t1)で、目標空燃比A/Ftがリッチ空燃比A/Frに切り替えられる。このように目標空燃比A/FtはOセンサ18の出力をトリガにして反転される。
While performing the active air-fuel ratio control that performs such an air-fuel ratio change, the oxygen storage capacity OSC of the catalyst 11 is measured as follows, and the deterioration of the catalyst 11 is determined.
Before the time t1 shown in FIG. 3, the target air-fuel ratio A / Ft is set to the lean air-fuel ratio A / Fl, and the lean gas flows into the catalyst 11. At this time, the catalyst 11 continues to absorb oxygen, but when it fully absorbs oxygen, it can no longer absorb oxygen, and the lean gas flows through the catalyst 11 and flows downstream of the catalyst 11. When this happens, the post-catalyst air-fuel ratio A / Frr changes to the lean side, and when the output voltage of the O 2 sensor 18 reaches the lean determination value VL (t1), the target air-fuel ratio A / Ft becomes the rich air-fuel ratio A / Fr. Can be switched to. As described above, the target air-fuel ratio A / Ft is inverted with the output of the O 2 sensor 18 as a trigger.

そして、今度は触媒11にリッチガスが流入されることとなる。このとき触媒11では、それまで吸蔵されていた酸素が放出され続ける。触媒11から酸素が放出され続けると、やがて触媒11からは全ての吸蔵酸素が放出され尽くし、その時点でそれ以上酸素を放出できなくなり、リッチガスが触媒11を通り抜けて触媒11の下流側に流れ出す。こうなると触媒後空燃比A/Frrがリッチ側に変化し、Oセンサ18の出力電圧がリッチ判定値VRに達した時点(t2)で、目標空燃比A/Ftがリーン空燃比A/Flに切り替えられる。 This time, rich gas flows into the catalyst 11. At this time, the oxygen stored in the catalyst 11 continues to be released from the catalyst 11. If oxygen is continuously released from the catalyst 11, all of the stored oxygen is eventually released from the catalyst 11, and at that time, no more oxygen can be released, and rich gas flows through the catalyst 11 and flows downstream of the catalyst 11. When this happens, the post-catalyst air-fuel ratio A / Frr changes to the rich side, and the target air-fuel ratio A / Ft becomes the lean air-fuel ratio A / Fl when the output voltage of the O 2 sensor 18 reaches the rich determination value VR (t2). Can be switched to.

酸素吸蔵容量OSCが大きいほど、酸素を吸収或いは放出し続けることのできる時間が長くなる。つまり、触媒が劣化していない場合は目標空燃比A/Ftの反転周期(例えばt1からt2までの時間)が長くなり、触媒の劣化が進むほど目標空燃比A/Ftの反転周期は短くなる。   The larger the oxygen storage capacity OSC, the longer the time during which oxygen can be absorbed or released. That is, when the catalyst is not deteriorated, the inversion cycle of the target air-fuel ratio A / Ft (for example, the time from t1 to t2) becomes longer, and the inversion cycle of the target air-fuel ratio A / Ft becomes shorter as the deterioration of the catalyst proceeds. .

そこで、このことを利用して酸素吸蔵容量OSCが以下のようにして計測される。図4に示すように、時刻t1で目標空燃比A/Ftがリッチ空燃比A/Frに切り替えられた直後、僅かに遅れて実際値としての触媒前空燃比A/Ffrがリッチ空燃比A/Frに切り替わる。そして触媒前空燃比A/Ffrが理論空燃比A/Fsに達した時点t11から、次に目標空燃比A/Ftが反転する時点t2まで、次式(1)により、所定の微小時間毎の酸素吸蔵容量dOSC(酸素吸蔵容量の瞬時値)が算出され、且つこの微小時間毎の酸素吸蔵容量dOSCが時刻t11から時刻t2まで積算される。こうしてこの酸素放出サイクルにおける酸素吸蔵容量即ち放出酸素量が計測される。   Therefore, using this fact, the oxygen storage capacity OSC is measured as follows. As shown in FIG. 4, immediately after the target air-fuel ratio A / Ft is switched to the rich air-fuel ratio A / Fr at time t1, the pre-catalyst air-fuel ratio A / Ffr as the actual value is slightly delayed with the rich air-fuel ratio A / Fr. Switch to Fr. From the time t11 when the pre-catalyst air-fuel ratio A / Ffr reaches the theoretical air-fuel ratio A / Fs to the time t2 when the target air-fuel ratio A / Ft next reverses, the following equation (1) An oxygen storage capacity dOSC (instantaneous value of the oxygen storage capacity) is calculated, and the oxygen storage capacity dOSC for each minute time is integrated from time t11 to time t2. Thus, the oxygen storage capacity, that is, the amount of released oxygen in this oxygen release cycle is measured.

Figure 2009127597
Figure 2009127597

ここで、Qは燃料噴射量であり、空燃比差ΔA/Fに燃料噴射量Qを乗じるとストイキに対し不足又は過剰分の空気量を算出できる。Kは空気に含まれる酸素割合(約0.23)を表す定数である。   Here, Q is a fuel injection amount. When the air-fuel ratio difference ΔA / F is multiplied by the fuel injection amount Q, an air amount that is insufficient or excessive with respect to the stoichiometry can be calculated. K is a constant representing the proportion of oxygen contained in air (about 0.23).

基本的には、この1回で計測された酸素吸蔵容量OSCを用い、これを所定の劣化判定値OSCsと比較し、酸素吸蔵容量OSCが劣化判定値OSCsを超えていれば正常、酸素吸蔵容量OSCが劣化判定値OSCs以下ならば劣化、というように触媒の劣化を判定できる。精度を向上させるため、目標空燃比A/Ftがリーン側となっている酸素吸蔵サイクルでも同様に酸素吸蔵容量(この場合酸素吸蔵量)を計測し、これら酸素吸蔵容量の平均値を1吸放出サイクルに係る1単位の酸素吸蔵容量として計測することもできる。そしてさらに、吸放出サイクルを複数回繰り返し、複数単位の酸素吸蔵容量の値を得、その平均値を最終的な酸素吸蔵容量計測値とし、劣化判定値と比較して、最終的な劣化判定を行うこともできる。なお、触媒が劣化と判定されたときにはその事実をユーザ(ドライバ)に告知するため、図示しない警告装置(チェックランプ等)を作動させるのが好ましい。   Basically, the oxygen storage capacity OSC measured at one time is used and compared with a predetermined deterioration judgment value OSCs. If the oxygen storage capacity OSC exceeds the deterioration judgment value OSCs, the oxygen storage capacity is normal. If the OSC is equal to or lower than the deterioration determination value OSCs, the deterioration of the catalyst can be determined such as deterioration. In order to improve accuracy, the oxygen storage capacity (in this case, oxygen storage amount) is also measured in the oxygen storage cycle where the target air-fuel ratio A / Ft is on the lean side, and the average value of these oxygen storage capacities is absorbed and released by 1 It can also be measured as an oxygen storage capacity of one unit related to the cycle. Further, the absorption / release cycle is repeated a plurality of times to obtain a value of the oxygen storage capacity of a plurality of units, and the average value is used as the final oxygen storage capacity measurement value, and compared with the deterioration determination value, the final deterioration determination is performed. It can also be done. When it is determined that the catalyst is deteriorated, it is preferable to operate a warning device (such as a check lamp) not shown in order to notify the user (driver) of the fact.

酸素吸蔵サイクルにおける酸素吸蔵容量(酸素吸蔵量)の計測については、図4に示すように、時刻t2で目標空燃比A/Ftがリーン空燃比A/Flに切り替えられた後、触媒前空燃比A/Ffrが中心空燃比A/Fcに達した時点t21から、次に目標空燃比A/Ftがリッチ側に反転する時点t3まで、前式(1)により微小時間毎の酸素吸蔵容量dOSCが算出され、且つこの微小時間毎の酸素吸蔵容量dOSCが積算される。こうしてこの酸素吸収サイクルにおける酸素吸蔵容量OSC即ち吸蔵酸素量(図4のOSC2)が計測される。前回サイクルの酸素吸蔵容量OSC1と今回サイクルの酸素吸蔵容量OSC2とはほぼ等しい値となるはずである。   Regarding the measurement of the oxygen storage capacity (oxygen storage amount) in the oxygen storage cycle, as shown in FIG. 4, after the target air-fuel ratio A / Ft is switched to the lean air-fuel ratio A / Fl at time t2, the pre-catalyst air-fuel ratio is measured. From the time point t21 when A / Ffr reaches the central air-fuel ratio A / Fc to the time point t3 when the target air-fuel ratio A / Ft is reversed to the rich side next, the oxygen storage capacity dOSC for each minute time is calculated from the previous equation (1). The calculated oxygen storage capacity dOSC for each minute time is integrated. Thus, the oxygen storage capacity OSC, that is, the amount of stored oxygen (OSC2 in FIG. 4) in this oxygen absorption cycle is measured. The oxygen storage capacity OSC1 of the previous cycle and the oxygen storage capacity OSC2 of the current cycle should be approximately equal.

次に、燃料中の硫黄濃度を考慮した触媒劣化診断について図5ないし図8を参照して説明する。
ここで、図5は触媒11の上流の空燃比をアクティブ制御によりリッチとリーンの間で切り替えたときの空燃比センサ及びOセンサの出力波形例を示すグラフであって、(1)が高硫黄燃料、(2)が低硫黄燃料の場合である。
アクティブ制御時のOセンサ18の出力波形は、図5(B)からわかるように、燃料の硫黄濃度が高い高硫黄燃料(1)の場合には、一端リッチ側にピーキーな出力波形(最大値)をとり、その後若干リーン側にシフトして(落ち込んで)、略定常状態となる定常値をとり、その後しばらくしてリーン出力となる。
燃料の硫黄濃度が低い低硫黄燃料(2)の場合には、リーンからリッチ、リッチからリーンと単純に変化する波形となるが、これと比べると、高硫黄燃料(1)の場合の出力波形は、特有の波形形状を有している。
高硫黄燃料(1)の場合に、Oセンサ18の出力波形がリッチ出力後にリーン側にシフトする理由は、触媒11上の酸素を吸蔵する部分が硫黄で覆われ、吸蔵されずに触媒11上をすり抜けるリーンガスが低硫黄燃料(2)の場合と比べて多いためであり、Oセンサ18の出力がリーン反転するまでには至らない程度のガス濃度であるためと考えられる。すなわち、A/Fのリーン制御により、触媒11に流入してきたOは、触媒11に吸蔵されるが、硫黄が存在する場合には、硫黄により反応が鈍ることで吸蔵しきれないOが触媒11の下流のOセンサ18に達するため、リッチ側に最大値をとり、その後若干リーン側に落ち込んで略定常値をとると考えられる。
本実施形態では、この高硫黄燃料(1)に特有の出力波形形状を検出することにより、燃料の硫黄濃度を判別する。
Next, the catalyst deterioration diagnosis in consideration of the sulfur concentration in the fuel will be described with reference to FIGS.
Here, FIG. 5 is a graph showing examples of output waveforms of the air-fuel ratio sensor and the O 2 sensor when the air-fuel ratio upstream of the catalyst 11 is switched between rich and lean by active control. This is a case where sulfur fuel (2) is a low sulfur fuel.
As can be seen from FIG. 5B, the output waveform of the O 2 sensor 18 during active control is a peak output waveform (maximum) on the rich side in the case of a high sulfur fuel (1) having a high sulfur concentration in the fuel. Value), and then shifts slightly to the lean side (falls), takes a steady value that becomes a substantially steady state, and after a while becomes a lean output.
In the case of the low sulfur fuel (2) having a low sulfur concentration of the fuel, the waveform changes simply from lean to rich and from rich to lean. Compared with this, the output waveform in the case of the high sulfur fuel (1) Has a unique waveform shape.
In the case of the high sulfur fuel (1), the reason why the output waveform of the O 2 sensor 18 shifts to the lean side after the rich output is that the oxygen storage portion on the catalyst 11 is covered with sulfur and the catalyst 11 is not stored. This is because the amount of lean gas that passes through is higher than that of the low-sulfur fuel (2), and the gas concentration is such that the output of the O 2 sensor 18 does not reach the lean reversal. That is, O 2 that has flowed into the catalyst 11 by the lean control of A / F is occluded in the catalyst 11, but when sulfur is present, O 2 that cannot be occluded due to the reaction being dulled by sulfur. In order to reach the O 2 sensor 18 downstream of the catalyst 11, it is considered that the maximum value is taken on the rich side, then falls slightly to the lean side and takes a substantially steady value.
In the present embodiment, the sulfur concentration of the fuel is determined by detecting the output waveform shape peculiar to the high sulfur fuel (1).

ここで、図6に示すように、高硫黄燃料(1)に特有の出力波形形状の特徴を表すパラメータを定義する。
図6(B)において、OXSMAXは、(A)に示す目標空燃比(A/F目標)がリーン反転している間のOセンサ18の出力の最大値(ピーク値)である。
OXSMIDは、A)に示す目標空燃比(A/F目標)がリーン反転している間に、Oセンサ18の出力がOXSMAXからリーン側へ低下して略定常状態に保持される定常値である。
ΔOXSは、OXSMAXとOXSMIDとの差である。本実施形態では、このΔOXSが所定の閾値よりも大きいことが、高硫黄燃料と判断する条件(A)とする。
図6(C)において、diff1,diff2,diff3は、Oセンサ18の出力の偏差(微分)値であり、リーン反転中にdiff1となり、その後、Oセンサ18の出力がリーン側にシフトする際にマイナス(diff2)となり、その後、リーン出力への低下の傾きが小さくなるので、diff3はdiff2よりも大きな値となる。
本実施形態では、diff1>diff2かつdiff2<diff3の条件を満たすことが、高硫黄燃料の出力波形形状の特徴を有している条件(B)とする。
Here, as shown in FIG. 6, parameters representing the characteristics of the output waveform shape peculiar to the high sulfur fuel (1) are defined.
In FIG. 6B, OXSMAX is the maximum value (peak value) of the output of the O 2 sensor 18 while the target air-fuel ratio (A / F target) shown in FIG.
OXSMID is a steady value at which the output of the O 2 sensor 18 decreases from OXSMAX to the lean side and is maintained in a substantially steady state while the target air-fuel ratio (A / F target) shown in A) is lean-reversed. is there.
ΔOXS is the difference between OXSMAX and OXSMID. In the present embodiment, the condition (A) for determining that the high sulfur fuel is that ΔOXS is larger than a predetermined threshold value.
In FIG. 6C, diff1, diff2, and diff3 are deviation (differential) values of the output of the O 2 sensor 18, become diff1 during lean inversion, and then the output of the O 2 sensor 18 shifts to the lean side. At this time, it becomes minus (diff2), and thereafter, the slope of the decrease to the lean output becomes small, so that diff3 is larger than diff2.
In this embodiment, satisfying the conditions of diff1> diff2 and diff2 <diff3 is the condition (B) having the characteristics of the output waveform shape of the high sulfur fuel.

ここで、図7は、ECU20による燃料中の硫黄濃度を考慮した触媒劣化検出処理の一例を示すフローチャートである。尚、図7に示す処理は、例えば、所定時間毎に繰り返し実行される。
先ず、所定の触媒劣化検出を実行する条件が成立しているかを判断し(ステップS1)、成立している場合には、空燃比アクティブ制御を開始する(ステップS2)。
Here, FIG. 7 is a flowchart showing an example of the catalyst deterioration detection process in consideration of the sulfur concentration in the fuel by the ECU 20. Note that the processing shown in FIG. 7 is repeatedly executed, for example, every predetermined time.
First, it is determined whether a condition for executing a predetermined catalyst deterioration detection is satisfied (step S1). If the condition is satisfied, air-fuel ratio active control is started (step S2).

そして、Oセンサ18の出力波形から、OXSMAX,OXSMID,diff1,diff2,diff3を取得し、先ず上記条件(A)の判別をする。すなわち、ΔOXS=OXSMAX−OXSMIDと所定の閾値とを比較し(ステップS3)、ΔOXSが所定の閾値以下の場合には、使用燃料が高硫黄燃料ではない(低硫黄燃料)と判別する(ステップS6)。 Then, OXSMAX, OXSMID, diff1, diff2, and diff3 are acquired from the output waveform of the O 2 sensor 18, and the condition (A) is first discriminated. That is, ΔOXS = OXSMAX−OXSMID is compared with a predetermined threshold (step S3), and when ΔOXS is equal to or smaller than the predetermined threshold, it is determined that the fuel used is not a high sulfur fuel (low sulfur fuel) (step S6). ).

ΔOXSが所定の閾値より大きい場合には、上記条件(B)の判別、すなわち、diff1>diff2かつdiff2<diff3の条件を満たすかを判断する(ステップS4)。
diff1>diff2かつdiff2<diff3の条件を満たす場合には、使用燃料が高硫黄燃料と判別する(ステップS5)。この条件を満たさない場合には、使用燃料が高硫黄燃料ではない(低硫黄燃料)と判別する(ステップS6)。
If ΔOXS is larger than the predetermined threshold, it is determined whether the condition (B) is satisfied, that is, whether the conditions of diff1> diff2 and diff2 <diff3 are satisfied (step S4).
When the conditions of diff1> diff2 and diff2 <diff3 are satisfied, it is determined that the fuel used is a high sulfur fuel (step S5). If this condition is not satisfied, it is determined that the fuel used is not a high sulfur fuel (low sulfur fuel) (step S6).

使用燃料が高硫黄燃料と判別した場合には、この後の処理の触媒劣化判断に用いる補正量を算出する(ステップS7)。この補正量は、触媒劣化判断に用いる酸素吸蔵容量または触媒劣化を判断するための判定値を補正するためのものである。尚、この補正量については後述する。   If it is determined that the fuel used is a high sulfur fuel, a correction amount used for determining catalyst deterioration in the subsequent processing is calculated (step S7). This correction amount is for correcting the oxygen storage capacity used for determining catalyst deterioration or the determination value for determining catalyst deterioration. This correction amount will be described later.

次いで、ステップS5、S6における判別結果を考慮して、触媒劣化を判断する(ステップS8)。触媒劣化の判断は、基本的には、図8に示すように、触媒上流空燃比のアクティブ制御時の触媒11の酸素吸蔵容量(OSC)に基いて判断する。すなわち、計測した触媒11のOSCと異常判定値JVとを比較し、OSCが異常判定値JVよりも大きい場合には、正常判定とし、異常判定値JV以下の場合には異常判定とする。   Next, catalyst degradation is determined in consideration of the determination results in steps S5 and S6 (step S8). The determination of catalyst deterioration is basically made based on the oxygen storage capacity (OSC) of the catalyst 11 during active control of the catalyst upstream air-fuel ratio, as shown in FIG. That is, the measured OSC of the catalyst 11 is compared with the abnormality determination value JV. When the OSC is larger than the abnormality determination value JV, the determination is normal, and when the OSC is less than the abnormality determination value JV, the determination is abnormal.

ここで、使用燃料が高硫黄燃料の場合には、図8に示すように、そのOSCの値OSC_Hは、使用燃料が低硫黄燃料の場合のOSCの値OSC_Lと比べて小さくなる。
本実施形態では、触媒劣化の判断への硫黄濃度の影響を省くために、硫黄濃度の判別結果に応じて、触媒劣化判断に用いるOSCまたは触媒劣化を判断するための異常判定値JVをステップS7で算出した補正量で補正する。
Here, when the fuel used is a high sulfur fuel, as shown in FIG. 8, the OSC value OSC_H is smaller than the OSC value OSC_L when the fuel used is a low sulfur fuel.
In this embodiment, in order to eliminate the influence of the sulfur concentration on the determination of the catalyst deterioration, the OSC used for the catalyst deterioration determination or the abnormality determination value JV for determining the catalyst deterioration is determined in accordance with the determination result of the sulfur concentration in step S7. Correct with the correction amount calculated in.

使用燃料が高硫黄燃料と判別された場合には、例えば、測定されたOSCに所定の補正量α1を掛け合わせて低硫黄燃料と同等の値に補正する。あるいは、測定されたOSCに所定の補正量α2を足し合わせて低硫黄燃料と同等の値に補正する。   When the used fuel is determined to be a high sulfur fuel, for example, the measured OSC is multiplied by a predetermined correction amount α1 to be corrected to a value equivalent to that of the low sulfur fuel. Alternatively, a predetermined correction amount α2 is added to the measured OSC to correct it to a value equivalent to that of the low sulfur fuel.

硫黄濃度の影響を省くための他の補正方法として、使用燃料が高硫黄燃料と判別された場合には、例えば、異常判別値JVから所定の補正量β1を引いて新たな異常判別値JV1に引き下げる、あるいは、異常判別値JVに所定の補正量β2を掛け合わせて新たな異常判別値JV1に引き下げることが考えられる。   As another correction method for eliminating the influence of the sulfur concentration, when the fuel used is determined to be high sulfur fuel, for example, a predetermined correction amount β1 is subtracted from the abnormality determination value JV to obtain a new abnormality determination value JV1. It is conceivable to lower the value or to multiply the abnormality determination value JV by a predetermined correction amount β2 to reduce it to a new abnormality determination value JV1.

上記実施形態では、硫黄濃度が高いか低いかを判別したが、これに限定されるわけではなく、硫黄濃度を段階的に判別することも可能であり、この場合には、測定されたOSC又は異常判別値を補正する場合に、補正量は硫黄濃度に応じて変える構成とすることが可能である。   In the above embodiment, it is determined whether the sulfur concentration is high or low. However, the present invention is not limited to this, and it is also possible to determine the sulfur concentration step by step. In this case, the measured OSC or When the abnormality determination value is corrected, the correction amount can be changed according to the sulfur concentration.

本発明の一実施形態の構成を示す概略図である。It is the schematic which shows the structure of one Embodiment of this invention. 触媒の構成を示す概略断面図である。It is a schematic sectional drawing which shows the structure of a catalyst. アクティブ空燃比制御を説明するためのタイムチャートである。It is a time chart for demonstrating active air fuel ratio control. 図3と同様のタイムチャートであり、酸素吸蔵容量の計測方法を説明するための図である。FIG. 4 is a time chart similar to FIG. 3 for illustrating a method for measuring the oxygen storage capacity. 触媒上流空燃比をアクティブ制御によりリッチとリーンの間で切り替えたときの空燃比センサ及びOセンサの出力波形例を示すグラフである。Is a graph showing an output waveform example of the air-fuel ratio sensor and the O 2 sensor when switching between the rich and lean by the active control of the catalyst upstream air-fuel ratio. 高硫黄燃料に特有の出力波形形状の特徴を表すパラメータを定義するための図である。It is a figure for defining the parameter showing the characteristic of the output waveform shape peculiar to high sulfur fuel. 本発明の一実施形態に係る触媒劣化検出処理の手順を示すフローチャートである。It is a flowchart which shows the procedure of the catalyst deterioration detection process which concerns on one Embodiment of this invention. 燃料中の硫黄濃度を考慮に入れた触媒劣化の判別方法を説明するための図である。It is a figure for demonstrating the determination method of catalyst deterioration which considered the sulfur concentration in a fuel.

符号の説明Explanation of symbols

1…内燃機関
6…排気管
11…触媒
12…インジェクタ
14…クランク角センサ
15…アクセル開度センサ
17…空燃比センサ
18…Oセンサ
20…電子制御ユニット(ECU)
1 ... engine 6 ... exhaust pipe 11 ... catalyst 12 ... injector 14 ... crank angle sensor 15 ... accelerator opening sensor 17 ... air-fuel ratio sensor 18 ... O 2 sensor 20 ... electronic control unit (ECU)

Claims (3)

内燃機関の排気通路に配置された触媒の劣化を診断する内燃機関の触媒劣化診断装置であって、
燃料中の硫黄濃度を判別する硫黄濃度判別手段と、
前記硫黄濃度判別手段の判別結果を考慮して触媒劣化を判断する触媒劣化判断手段と、を有し、
前記硫黄濃度判別手段は、触媒上流の空燃比をアクティブ制御によりリッチからリーンに切り替えたときの、触媒下流の酸素センサの出力値のリッチ側最大値
と、このリッチ側最大値からリーン側へ値が落ち込んでほぼ定常状態となったときの定常値との差に基づいて、燃料中の硫黄濃度を判別する、
ことを特徴とする内燃機関の触媒劣化診断装置。
A catalyst deterioration diagnosis device for an internal combustion engine for diagnosing deterioration of a catalyst disposed in an exhaust passage of the internal combustion engine,
Sulfur concentration determining means for determining the sulfur concentration in the fuel;
Catalyst deterioration determination means for determining catalyst deterioration in consideration of the determination result of the sulfur concentration determination means,
The sulfur concentration discriminating means has a value on the rich side of the output value of the oxygen sensor downstream of the catalyst when the air-fuel ratio upstream of the catalyst is switched from rich to lean by active control, and a value from the rich side maximum value to the lean side. To determine the sulfur concentration in the fuel based on the difference from the steady state value when it becomes almost steady state.
An apparatus for diagnosing catalyst deterioration in an internal combustion engine.
前記硫黄濃度判別手段は、燃料中の硫黄濃度を判別する際に、前記リッチ側最大値と定常値との差に加えて、前記触媒下流の酸素センサの出力波形形状が高硫黄燃料特有の形状をとるか否かを判断する、
ことを特徴とする請求項1に記載の触媒劣化診断装置。
When the sulfur concentration determination means determines the sulfur concentration in the fuel, in addition to the difference between the rich side maximum value and the steady value, the output waveform shape of the oxygen sensor downstream of the catalyst is a shape peculiar to high sulfur fuel. To decide whether or not to take
The catalyst deterioration diagnosis apparatus according to claim 1.
前記触媒劣化判断手段は、触媒上流空燃比のアクティブ制御時の触媒の酸素吸蔵容量に基いて触媒劣化を判断し、
前記硫黄濃度判別手段の判別結果に応じて、触媒劣化判断に用いる酸素吸蔵容量または触媒劣化を判断するための判定値を補正する、
ことを特徴とする請求項1又は2に記載の触媒劣化診断装置。
The catalyst deterioration determining means determines catalyst deterioration based on the oxygen storage capacity of the catalyst during active control of the catalyst upstream air-fuel ratio,
According to the determination result of the sulfur concentration determination means, the oxygen storage capacity used for the catalyst deterioration determination or the determination value for determining the catalyst deterioration is corrected.
The catalyst deterioration diagnosis device according to claim 1 or 2, wherein
JP2007306443A 2007-11-27 2007-11-27 Catalyst degradation diagnostic device Pending JP2009127597A (en)

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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2012031762A (en) * 2010-07-29 2012-02-16 Toyota Motor Corp Catalyst abnormality diagnostic system
US8649956B2 (en) 2010-05-20 2014-02-11 Toyota Jidosha Kabushiki Kaisha Apparatus for acquiring responsibility of oxygen concentration sensor
US8670917B2 (en) 2009-10-06 2014-03-11 Toyota Jidosha Kabushiki Kaisha Air-fuel-ratio imbalance determination apparatus for internal combustion engine
CN104279035A (en) * 2013-07-11 2015-01-14 苏州奥易克斯汽车电子有限公司 Diagnosis method for catalytic converter of engine
KR20190068971A (en) * 2017-12-11 2019-06-19 현대자동차주식회사 Exhaust gas post processing system and control method thereof

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US8670917B2 (en) 2009-10-06 2014-03-11 Toyota Jidosha Kabushiki Kaisha Air-fuel-ratio imbalance determination apparatus for internal combustion engine
US8649956B2 (en) 2010-05-20 2014-02-11 Toyota Jidosha Kabushiki Kaisha Apparatus for acquiring responsibility of oxygen concentration sensor
JP2012031762A (en) * 2010-07-29 2012-02-16 Toyota Motor Corp Catalyst abnormality diagnostic system
CN104279035A (en) * 2013-07-11 2015-01-14 苏州奥易克斯汽车电子有限公司 Diagnosis method for catalytic converter of engine
KR20190068971A (en) * 2017-12-11 2019-06-19 현대자동차주식회사 Exhaust gas post processing system and control method thereof
KR102451900B1 (en) * 2017-12-11 2022-10-06 현대자동차 주식회사 Exhaust gas post processing system and control method thereof

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