JP2007177646A - Catalyst temperature estimating apparatus of internal combustion engine - Google Patents

Catalyst temperature estimating apparatus of internal combustion engine Download PDF

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JP2007177646A
JP2007177646A JP2005374806A JP2005374806A JP2007177646A JP 2007177646 A JP2007177646 A JP 2007177646A JP 2005374806 A JP2005374806 A JP 2005374806A JP 2005374806 A JP2005374806 A JP 2005374806A JP 2007177646 A JP2007177646 A JP 2007177646A
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catalyst
fuel ratio
amount
air
exhaust
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JP4635864B2 (en
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Shinichi Soejima
慎一 副島
Noriyasu Adachi
憲保 足立
Ryuzo Kayama
竜三 加山
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Denso Corp
Toyota Motor Corp
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Toyota Motor Corp
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Abstract

<P>PROBLEM TO BE SOLVED: To accurately obtain the temperature of an exhaust gas purifying catalyst even when a catalyst is disposed upstream of the exhaust gas purifying catalyst in an internal combustion engine in which a plurality of cylinder groups are operated at different air-fuel ratios, and the exhaust exhausted from the cylinder groups is merged into, then flowed into the exhaust gas purifying catalyst. <P>SOLUTION: A catalyst temperature estimating apparatus of the internal combustion engine comprises a plurality of exhaust branch pipes connected to a plurality of the cylinder groups of the internal combustion engine respectively, a merging exhaust pipe to merge a plurality of the exhaust branch pipes, a first catalyst disposed in the merging exhaust pipe, and a second catalyst 12 disposed in the exhaust branch pipes of the cylinder groups which are operated at a rich air fuel ratio when performing air fuel ratio independent control to operate a part of a plurality of the cylinder groups at a rich air fuel ratio, while the other cylinder groups are operated at a lean air fuel ratio. In this case, a floor temperature Tcat2 of the first catalyst is estimated in consideration of an unburned fuel component quantity which reacts with the second catalyst (S106). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

本発明は、内燃機関の排気経路に配置された排気浄化触媒の温度を推定する技術に関する。   The present invention relates to a technique for estimating the temperature of an exhaust purification catalyst disposed in an exhaust path of an internal combustion engine.

2つの気筒群を有する内燃機関と、2つの気筒群の各々に接続された排気枝管と、2つの排気枝管を合流させた排気管と、排気管に配置された排気浄化触媒とを備え、2つの気筒群の一方をリッチ空燃比で運転させるとともに他方をリーン空燃比で運転させることにより、未燃燃料成分と酸素を含有した排気を排気浄化触媒へ供給する技術が知られている。   An internal combustion engine having two cylinder groups, an exhaust branch pipe connected to each of the two cylinder groups, an exhaust pipe joining the two exhaust branch pipes, and an exhaust purification catalyst disposed in the exhaust pipe A technique is known in which one of the two cylinder groups is operated at a rich air-fuel ratio and the other is operated at a lean air-fuel ratio to supply exhaust gas containing unburned fuel components and oxygen to an exhaust purification catalyst.

上記したような技術においては、排気浄化触媒へ流入する排気の空燃比が理論空燃比となるように各気筒群の空燃比をフィードバック制御するとともに、その際のフィードバック制御の目標値とリッチ空燃比で運転される気筒群のリッチ度合いとから触媒床温を推定する技術も提案されている(例えば、特許文献1を参照)。
特開2001−132498号公報 特開平8−189388号公報 特開2001−227369号公報 特開2000−64824号公報
In the technology as described above, the air-fuel ratio of each cylinder group is feedback-controlled so that the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst becomes the stoichiometric air-fuel ratio, and the target value of the feedback control and the rich air-fuel ratio at that time There has also been proposed a technique for estimating the catalyst bed temperature from the richness of the cylinder group operated at (for example, see Patent Document 1).
JP 2001-132498 A JP-A-8-189388 JP 2001-227369 A JP 2000-64824 A

ところで、排気浄化触媒より上流の排気枝管に触媒が設けられると、その触媒においても未燃燃料成分が反応する。このため、前記触媒における未燃燃料成分の反応如何によって排気浄化触媒の温度が変化する可能性がある。   By the way, when a catalyst is provided in the exhaust branch pipe upstream from the exhaust purification catalyst, the unburned fuel component also reacts in the catalyst. For this reason, the temperature of the exhaust purification catalyst may change depending on the reaction of the unburned fuel component in the catalyst.

本発明の目的は、内燃機関の複数の気筒群から排出された排気を合流させた後に排気浄化触媒へ流入させる構成において、排気浄化触媒より上流に触媒が配置された場合であっても排気浄化触媒の温度を正確に取得することにある。   An object of the present invention is to purify exhaust gas even when a catalyst is disposed upstream of the exhaust purification catalyst in a configuration in which exhaust gases discharged from a plurality of cylinder groups of an internal combustion engine are joined and then flowed into the exhaust purification catalyst. It is to obtain the temperature of the catalyst accurately.

本発明は、上記した課題を解決するために、以下のような手段を採用した。すなわち、本発明に係る内燃機関の触媒温度推定装置は、内燃機関の複数の気筒群に各々接続された複数の排気枝管と、前記複数の排気枝管を合流させた合流排気管と、前記合流排気管に配置された第1触媒と、前記複数の気筒群の一部をリッチ空燃比で運転させるとともに残余の気筒群をリーン空燃比で運転させる空燃比独立制御を行う制御手段と、前記空燃比独立制御の実行時にリッチ空燃比で運転させられる気筒群の排気枝管に配置された第2触媒と、前記空燃比独立制御の実行時に前記第2触媒で反応する未燃燃料成分の量に基づいて前記第1触媒の温度を推定する推定手段と、を備えるようにした。   The present invention employs the following means in order to solve the above-described problems. That is, a catalyst temperature estimation device for an internal combustion engine according to the present invention includes a plurality of exhaust branch pipes respectively connected to a plurality of cylinder groups of the internal combustion engine, a combined exhaust pipe obtained by joining the plurality of exhaust branch pipes, A first catalyst disposed in a combined exhaust pipe; and control means for performing air-fuel ratio independent control for operating part of the plurality of cylinder groups at a rich air-fuel ratio and operating the remaining cylinder groups at a lean air-fuel ratio; The amount of the unburned fuel component that reacts with the second catalyst disposed in the exhaust branch pipe of the cylinder group that is operated at the rich air-fuel ratio when executing the air-fuel ratio independent control and the second catalyst when executing the air-fuel ratio independent control. And estimating means for estimating the temperature of the first catalyst based on the above.

かかる内燃機関の触媒温度推定装置によれば、複数の気筒群の一部がリッチ空燃比で運転させられるとともに残余の気筒群がリーン空燃比で運転させられる空燃比独立制御が行われた時に、第2触媒で反応する未燃燃料成分の量に基づいて第1触媒の温度が推定される。   According to such a catalyst temperature estimation device for an internal combustion engine, when air-fuel ratio independent control is performed in which some of the plurality of cylinder groups are operated at a rich air-fuel ratio and the remaining cylinder groups are operated at a lean air-fuel ratio, The temperature of the first catalyst is estimated based on the amount of the unburned fuel component that reacts with the second catalyst.

この場合、第1触媒へ供給される未燃燃料成分の量、言い換えれば第1触媒において酸化される未燃燃料成分量を特定することができるため、第1触媒が授受する熱量を正確に
求めることが可能となる。その結果、第1触媒の温度を正確に特定することが可能となる。
In this case, since the amount of unburned fuel component supplied to the first catalyst, in other words, the amount of unburned fuel component oxidized in the first catalyst can be specified, the amount of heat transferred by the first catalyst is accurately obtained. It becomes possible. As a result, it is possible to accurately specify the temperature of the first catalyst.

本発明に係る内燃機関の触媒温度推定装置において、推定手段は、例えば、空燃比独立制御の実行時にリッチ空燃比で運転される気筒群から排出される未燃燃料成分量を演算し、算出された未燃燃料成分量から前記第2触媒で反応する未燃燃料成分量を減算して前記第1触媒へ流入する未燃燃料成分量を算出し、前記第1触媒へ流入する未燃燃料成分量のうち該第1触媒で反応する未燃燃料成分を演算し、前記第1触媒で反応する未燃燃料成分量から前記第1触媒の温度を推定することができる。   In the catalyst temperature estimating apparatus for an internal combustion engine according to the present invention, the estimating means calculates, for example, an amount of unburned fuel component discharged from a cylinder group operated at a rich air-fuel ratio when executing air-fuel ratio independent control. The amount of unburned fuel component that reacts with the second catalyst is subtracted from the amount of unburned fuel component calculated to calculate the amount of unburned fuel component that flows into the first catalyst, and the amount of unburned fuel component that flows into the first catalyst The unburned fuel component that reacts with the first catalyst out of the amount can be calculated, and the temperature of the first catalyst can be estimated from the unburned fuel component amount that reacts with the first catalyst.

尚、本願発明者の鋭意の実験及び検証により、第2触媒で反応する未燃燃料成分量は以下のような傾向を有していることが解った。   In addition, it was found from the diligent experiments and verifications of the present inventor that the amount of unburned fuel component that reacts with the second catalyst has the following tendency.

第1に、第2触媒で反応する未燃燃料成分量は、第2触媒へ流入する排気の空燃比が一定の空燃比より低い場合には排気の空燃比が高くなるほど多くなり、該第2触媒へ流入する排気の空燃比が一定空燃比を超えると略一定になる傾向を有する。   First, the amount of unburned fuel component that reacts with the second catalyst increases as the air-fuel ratio of the exhaust gas becomes higher when the air-fuel ratio of the exhaust gas flowing into the second catalyst is lower than a certain air-fuel ratio. When the air-fuel ratio of the exhaust gas flowing into the catalyst exceeds a certain air-fuel ratio, it tends to be substantially constant.

第2に、第2触媒で反応する未燃燃料成分量は、該第2触媒へ流入する排気の流量が多くなるほど少なくなる傾向を有する。   Second, the amount of unburned fuel component that reacts with the second catalyst tends to decrease as the flow rate of the exhaust gas flowing into the second catalyst increases.

第3に、第2触媒で反応する未燃燃料成分量は、第2触媒の温度が一定温度より低い場合には該第2触媒の温度が高くなるほど多くなり、第2触媒の温度が一定温度を超えると略一定になる。   Third, when the temperature of the second catalyst is lower than a certain temperature, the amount of the unburned fuel component that reacts with the second catalyst increases as the temperature of the second catalyst increases, and the temperature of the second catalyst increases. When it exceeds, it becomes almost constant.

依って、本発明に係る推定手段は、第2触媒へ流入する排気の空燃比、排気流量、及び第2触媒の温度に基づいて、第2触媒で反応する未燃燃料成分量を特定するようにしてもよい。   Therefore, the estimation means according to the present invention specifies the amount of unburned fuel component that reacts with the second catalyst based on the air-fuel ratio of the exhaust gas flowing into the second catalyst, the exhaust flow rate, and the temperature of the second catalyst. It may be.

また、空燃比独立制御が行われた場合には、リーン空燃比で運転される気筒群から排出された窒素酸化物(NO)が第1触媒へ流入する。窒素酸化物(NO)は還元される際に吸熱する特性を有しているため、第1触媒において窒素酸化物(NO)が還元されると第1触媒の温度が低下する。 Further, when the air-fuel ratio independent control is performed, nitrogen oxides (NO x ) discharged from the cylinder group operated at the lean air-fuel ratio flow into the first catalyst. Since nitrogen oxide (NO x ) has a characteristic of absorbing heat when it is reduced, the temperature of the first catalyst decreases when the nitrogen oxide (NO x ) is reduced in the first catalyst.

但し、空燃比独立制御が行われた際に第1触媒へ流入する窒素酸化物(NO)の量は、同時期に第1触媒へ流入する未燃燃料成分量に比して十分に少ないため、窒素酸化物(NO)による吸熱量を考慮しなくとも必要十分な温度推定精度を得られるが、窒素酸化物(NO)による吸熱量を考慮して推定精度を一層高めるようにしてもよい。 However, the amount of nitrogen oxide (NO x ) flowing into the first catalyst when air-fuel ratio independent control is performed is sufficiently smaller than the amount of unburned fuel components flowing into the first catalyst at the same time. Therefore, nitrogen oxides (NO x) is obtained a necessary and sufficient temperature estimation accuracy without considering heat absorption amount of, and the estimation accuracy to enhance more in consideration of the amount of heat absorbed by the nitrogen oxide (NO x) Also good.

本発明によれば、内燃機関の複数の気筒群から排出された排気を合流させた後に排気浄化触媒へ流入させる内燃機関において、排気浄化触媒より上流に触媒が配置された場合であっても排気浄化触媒の温度を正確に推定することができる。   According to the present invention, in an internal combustion engine in which exhaust gases discharged from a plurality of cylinder groups of an internal combustion engine are merged and then flowed into an exhaust purification catalyst, even if the catalyst is disposed upstream from the exhaust purification catalyst, The temperature of the purification catalyst can be accurately estimated.

以下、本発明の具体的な実施形態について図面に基づいて説明する。   Hereinafter, specific embodiments of the present invention will be described with reference to the drawings.

本発明の第1の実施例について図1〜図5に基づいて説明する。図1は、本発明を適用する内燃機関の概略構成を示す図である。   A first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine to which the present invention is applied.

図1に示す内燃機関1は、2つのバンク2、3を有するV型のエンジンである。各バンク2、3には、各々3つの気筒4が形成されている。各気筒4には、燃料噴射弁5から燃料が供給されるようになっている。尚、以下では、バンク2を第1気筒群2と称し、バンク3を第2気筒群3と称する。   The internal combustion engine 1 shown in FIG. 1 is a V-type engine having two banks 2 and 3. In each bank 2, 3, three cylinders 4 are formed. Each cylinder 4 is supplied with fuel from a fuel injection valve 5. Hereinafter, the bank 2 is referred to as a first cylinder group 2 and the bank 3 is referred to as a second cylinder group 3.

第1気筒群2と第2気筒群3には、吸気通路6を介して新気(空気)が導入されるようになっている。吸気通路6には、内燃機関1の吸入空気量Gaを測定するエアフローメータ7が取り付けられている。   Fresh air (air) is introduced into the first cylinder group 2 and the second cylinder group 3 via the intake passage 6. An air flow meter 7 for measuring the intake air amount Ga of the internal combustion engine 1 is attached to the intake passage 6.

また、第1気筒群2には第1排気枝管8が接続され、第2気筒群3には第2排気枝管9が接続されている。第1排気枝管8と第2排気枝管9は途中で合流して1本の排気管10を形成している。   A first exhaust branch pipe 8 is connected to the first cylinder group 2, and a second exhaust branch pipe 9 is connected to the second cylinder group 3. The first exhaust branch pipe 8 and the second exhaust branch pipe 9 are joined together to form one exhaust pipe 10.

排気管10には、メイン触媒11が配置されている。メイン触媒11は、本発明に係る第1触媒の一実施態様である。メイン触媒11としては、三元触媒、吸蔵還元型NO触媒、或いは選択還元型NO触媒等を用いることができる。 A main catalyst 11 is disposed in the exhaust pipe 10. The main catalyst 11 is an embodiment of the first catalyst according to the present invention. The main catalyst 11 can be used three-way catalyst, storage-reduction the NO x catalyst, or a selective reduction type NO x catalyst or the like.

第1排気枝管8と第2排気枝管9には、サブ触媒12、13が各々配置されている。尚、以下では、第1排気枝管8に配置されたサブ触媒12を第1サブ触媒12と称し、第2排気枝管9に配置されたサブ触媒13を第2サブ触媒13と称する。   Sub-catalysts 12 and 13 are arranged in the first exhaust branch pipe 8 and the second exhaust branch pipe 9, respectively. Hereinafter, the sub-catalyst 12 disposed in the first exhaust branch pipe 8 is referred to as a first sub-catalyst 12, and the sub-catalyst 13 disposed in the second exhaust branch pipe 9 is referred to as a second sub-catalyst 13.

前記した第1サブ触媒12及び第2サブ触媒13としては、酸化能を有する触媒を用いることができる。酸化能を有する触媒としては、酸化触媒、三元触媒、吸蔵還元型NO触媒、選択還元型NO触媒等を例示することができる。 As the first sub-catalyst 12 and the second sub-catalyst 13 described above, a catalyst having oxidation ability can be used. The catalyst having an oxidizing ability, an oxidation catalyst, three-way catalyst, storage-reduction the NO x catalyst, there can be exemplified a selective reduction type NO x catalyst or the like.

また、前記した排気管10のメイン触媒11より上流の部位には、排気温度センサ14と空燃比センサ15が配置され、メイン触媒11へ流入する排気の温度及び空燃比を検出することが可能になっている。   Further, an exhaust gas temperature sensor 14 and an air-fuel ratio sensor 15 are disposed in a portion of the exhaust pipe 10 upstream of the main catalyst 11 so that the temperature and air-fuel ratio of the exhaust gas flowing into the main catalyst 11 can be detected. It has become.

このように構成された内燃機関1には、該内燃機関1の運転状態を制御するための電子制御ユニット(ECU)16が併設されている。ECU16は、CPU、ROM、RAM、バックアップRAM等から構成される電子回路である。   The internal combustion engine 1 configured as described above is provided with an electronic control unit (ECU) 16 for controlling the operating state of the internal combustion engine 1. The ECU 16 is an electronic circuit composed of a CPU, ROM, RAM, backup RAM, and the like.

ECU16には、前述したエアフローメータ7、排気温度センサ14、或いは空燃比センサ15に加え、クランクポジションセンサ17等の各種センサの測定値が入力される。ECU16は、入力された各種測定値に基づいて燃料噴射弁5等を電気的に制御する。   In addition to the air flow meter 7, the exhaust gas temperature sensor 14, or the air-fuel ratio sensor 15, measured values of various sensors such as a crank position sensor 17 are input to the ECU 16. The ECU 16 electrically controls the fuel injection valve 5 and the like based on the inputted various measured values.

例えば、ECU16は、メイン触媒11を昇温させる必要がある場合に、第1気筒群2と第2気筒群3の何れか一方をリッチ空燃比で運転させるとともに他方をリーン空燃比で運転させるべく燃料噴射弁5を制御(以下、「空燃比独立制御」と称する)する。   For example, when the temperature of the main catalyst 11 needs to be raised, the ECU 16 operates one of the first cylinder group 2 and the second cylinder group 3 with a rich air-fuel ratio and the other with a lean air-fuel ratio. The fuel injection valve 5 is controlled (hereinafter referred to as “air-fuel ratio independent control”).

空燃比独立制御が行われた場合には、リッチ空燃比で運転された気筒群から排出される排気は、比較的多量の未燃燃料成分(主に炭化水素(HC))を含むガス(以下、「リッチ排気」と称する)となる。一方、リーン空燃比で運転された気筒群から排出される排気は、比較的多量の酸素(O)を含むガス(以下、「リーン排気」と称する)となる。 When the air-fuel ratio independent control is performed, the exhaust discharged from the cylinder group operated at the rich air-fuel ratio is a gas containing a relatively large amount of unburned fuel component (mainly hydrocarbon (HC)) , Referred to as “rich exhaust”). On the other hand, the exhaust discharged from the cylinder group operated at the lean air-fuel ratio becomes a gas containing a relatively large amount of oxygen (O 2 ) (hereinafter referred to as “lean exhaust”).

前記したリッチ排気とリーン排気は、第1排気枝管8及び第2排気枝管9を介して排気管10へ流入する。リッチ排気とリーン排気は排気管10において相互に混合してメイン触媒11へ流入する。   The rich exhaust gas and the lean exhaust gas flow into the exhaust pipe 10 through the first exhaust branch pipe 8 and the second exhaust branch pipe 9. The rich exhaust gas and the lean exhaust gas are mixed with each other in the exhaust pipe 10 and flow into the main catalyst 11.

リッチ排気とリーン排気の混合ガスがメイン触媒11へ流入すると、混合ガス中の未燃燃料成分が酸素(O)や窒素酸化物(NO)等と反応して熱を発生する。その結果、メイン触媒11は、未燃燃料成分の反応熱を受けて速やかに昇温する。 When the mixed gas of rich exhaust gas and lean exhaust gas flows into the main catalyst 11, the unburned fuel component in the mixed gas reacts with oxygen (O 2 ), nitrogen oxide (NO x ), etc., and generates heat. As a result, the main catalyst 11 rises quickly upon receiving the reaction heat of the unburned fuel component.

ところで、メイン触媒11の浄化率は、所定の温度域(温度浄化ウィンド)で有効となる。このため、上記した空燃比独立制御は、メイン触媒11の温度(床温)が前記した温度浄化ウィンドに収まるように行われることが好ましい。メイン触媒11の温度(床温)を温度浄化ウィンドに収めるためには、メイン触媒11の温度(床温)を正確に求める必要がある。   By the way, the purification rate of the main catalyst 11 is effective in a predetermined temperature range (temperature purification window). Therefore, the air-fuel ratio independent control described above is preferably performed so that the temperature (bed temperature) of the main catalyst 11 is within the temperature purification window. In order to store the temperature (bed temperature) of the main catalyst 11 in the temperature purification window, it is necessary to accurately determine the temperature (bed temperature) of the main catalyst 11.

メイン触媒11の温度(床温)は、メイン触媒11と排気との間で授受される熱量やメイン触媒11からの放熱量に加え、未燃燃料成分が酸素(O)や窒素酸化物(NO)と反応する際に発生する熱量の影響を受ける。 The temperature (floor temperature) of the main catalyst 11 includes not only the amount of heat transferred between the main catalyst 11 and the exhaust gas and the amount of heat released from the main catalyst 11, but also unburned fuel components such as oxygen (O 2 ) and nitrogen oxides ( affected heat generated during the reaction with NO x).

未燃燃料成分の反応熱量は、メイン触媒11へ供給される未燃燃料成分の量と相関する。そこで、空燃比センサ15の測定値A/F、エアフローメータ7の測定値Ga、及び燃料噴射弁5の燃料噴射量等をパラメータとしてメイン触媒11へ流入する未燃燃料成分量を推定する方法が考えられる。   The amount of reaction heat of the unburned fuel component correlates with the amount of unburned fuel component supplied to the main catalyst 11. Therefore, there is a method for estimating the amount of unburned fuel component flowing into the main catalyst 11 using the measured value A / F of the air-fuel ratio sensor 15, the measured value Ga of the air flow meter 7, the fuel injection amount of the fuel injection valve 5 and the like as parameters. Conceivable.

しかしながら、本実施例に示す内燃機関1のように第1排気枝管8及び第2排気枝管9に第1及び第2サブ触媒12、13が配置されていると、空燃比センサ15の測定値A/Fが同等であっても、排気中に含有される未燃燃料成分量が異なる場合がある。   However, when the first and second sub-catalysts 12 and 13 are arranged in the first exhaust branch pipe 8 and the second exhaust branch pipe 9 as in the internal combustion engine 1 shown in the present embodiment, the measurement by the air-fuel ratio sensor 15 is performed. Even if the values A / F are equal, the amount of unburned fuel components contained in the exhaust gas may be different.

リッチ排気に含まれる未燃燃料成分は、第1又は第2サブ触媒12、13において少なからず酸素(O)や窒素酸化物(NO)と反応する。一方、空燃比センサ15の測定値A/Fは、排気中に含まれる燃料成分が既に反応済みであるか或いは未反応であるかにかかわらず略同等になる場合がある。このため、空燃比センサ15の測定値A/Fが同等であっても、メイン触媒11へ供給される未燃燃料成分量が異なる可能性がある。 The unburned fuel component contained in the rich exhaust gas reacts with oxygen (O 2 ) or nitrogen oxide (NO x ) in the first or second sub-catalyst 12 or 13. On the other hand, the measured value A / F of the air-fuel ratio sensor 15 may be substantially the same regardless of whether the fuel component contained in the exhaust has already reacted or has not reacted. For this reason, even if the measured value A / F of the air-fuel ratio sensor 15 is the same, the amount of unburned fuel component supplied to the main catalyst 11 may be different.

依って、メイン触媒11の温度(床温)を正確に把握するためには、メイン触媒11へ供給される未燃燃料成分量を正確に特定する必要がある。   Therefore, in order to accurately grasp the temperature (bed temperature) of the main catalyst 11, it is necessary to accurately specify the amount of unburned fuel component supplied to the main catalyst 11.

そこで、本実施例に係る内燃機関の触媒温度推定装置では、メイン触媒11へ供給される未燃燃料成分量を正確に特定した上で、メイン触媒11の温度(床温)を推定するようにした。   Therefore, in the catalyst temperature estimation device for an internal combustion engine according to the present embodiment, the temperature (bed temperature) of the main catalyst 11 is estimated after accurately specifying the amount of unburned fuel component supplied to the main catalyst 11. did.

以下、メイン触媒11の温度(床温)を推定する方法について図2に沿って説明する。ここでは、空燃比独立制御において、第1気筒群2がリッチ空燃比で運転されるとともに、第2気筒群3がリーン空燃比で運転される場合を例に挙げる。この場合、第1サブ触媒12が本発明に係る第2触媒に相当する。   Hereinafter, a method for estimating the temperature (bed temperature) of the main catalyst 11 will be described with reference to FIG. Here, in the air-fuel ratio independent control, a case where the first cylinder group 2 is operated at a rich air-fuel ratio and the second cylinder group 3 is operated at a lean air-fuel ratio will be described as an example. In this case, the first sub-catalyst 12 corresponds to the second catalyst according to the present invention.

図2は、本実施例における温度推定ルーチンを示すフローチャートである。この温度推定ルーチンは、ECU16のROMに予め記憶されているルーチンであり、ECU16によって所定期間毎に繰り返し実行される。   FIG. 2 is a flowchart showing a temperature estimation routine in the present embodiment. This temperature estimation routine is a routine stored in advance in the ROM of the ECU 16 and is repeatedly executed by the ECU 16 at predetermined intervals.

温度推定ルーチンでは、ECU16は、先ず、S101において空燃比独立制御が実行されているか否かを判別する。S101において否定判定された場合は、ECU16は本ルーチンの実行を一旦終了する。一方、S101において肯定判定された場合は、ECU16は、S102へ進む。   In the temperature estimation routine, the ECU 16 first determines whether or not air-fuel ratio independent control is being executed in S101. If a negative determination is made in S101, the ECU 16 once terminates execution of this routine. On the other hand, if an affirmative determination is made in S101, the ECU 16 proceeds to S102.

S102では、ECU16は、エアフローメータ7の測定値Ga、機関回転数Ne、排気温度センサ14の測定値、空燃比センサ15の測定値A/F、第1気筒群2及び第2気筒群3の各々の気筒4に対する燃料噴射量等の各種データを読み込む。   In S102, the ECU 16 measures the measured value Ga of the air flow meter 7, the engine speed Ne, the measured value of the exhaust temperature sensor 14, the measured value A / F of the air-fuel ratio sensor 15, the first cylinder group 2 and the second cylinder group 3. Various data such as the fuel injection amount for each cylinder 4 is read.

S103では、ECU16は、第1気筒群2から排出される未燃燃料成分の総量ΣFを演算する。   In S103, the ECU 16 calculates the total amount ΣF of unburned fuel components discharged from the first cylinder group 2.

第1気筒群2の各気筒4では、各気筒4内に吸入された空気量に対して理論空燃比の混合気を形成することができる量の燃料が燃焼され、余剰の燃料は未燃のまま排出される。   In each cylinder 4 of the first cylinder group 2, an amount of fuel capable of forming a stoichiometric air-fuel mixture is burned with respect to the amount of air sucked into each cylinder 4, and surplus fuel is unburned. It is discharged as it is.

依って、第1気筒群2から排出される未燃燃料成分量の総量ΣFは、以下の式(1)により演算することができる。
ΣF=Gat1/(A/Fr)−Gat1/(A/Fs)・・・(1)
Therefore, the total amount ΣF of the unburned fuel component amount discharged from the first cylinder group 2 can be calculated by the following equation (1).
ΣF = Gat1 / (A / Fr) −Gat1 / (A / Fs) (1)

式(1)において、Gat1は、第1気筒群2の総吸入空気量であり、エアフローメータ7の測定値Gaを二等分した量である。A/Frは、第1気筒群2の空燃比であり、第1気筒群2の総吸入空気量Gat1を第1気筒群2の総燃料噴射量(1気筒当たりの燃料噴射量Qinjを三倍した量)で除算した値である。A/Fsは、理論空燃比(14.7
)である。
In Equation (1), Gat1 is the total intake air amount of the first cylinder group 2, and is an amount obtained by dividing the measured value Ga of the air flow meter 7 into two equal parts. A / Fr is the air-fuel ratio of the first cylinder group 2, and the total intake air amount Gat1 of the first cylinder group 2 is three times the total fuel injection amount of the first cylinder group 2 (the fuel injection amount Qinj per cylinder). The value divided by the amount). A / Fs is the stoichiometric air-fuel ratio (14.7
).

尚、第1気筒群2の空燃比A/Frは、第1サブ触媒12より上流の第1排気枝管8に空燃比センサ又は酸素濃度センサを取り付けて実測してもよい。   The air / fuel ratio A / Fr of the first cylinder group 2 may be measured by attaching an air / fuel ratio sensor or an oxygen concentration sensor to the first exhaust branch pipe 8 upstream of the first sub catalyst 12.

また、内燃機関1の燃料噴射量は、機関回転数Neと負荷率KLに基づいて定められるため、機関回転数Neと負荷率KLとをパラメータとするマップから未燃燃料成分量ΣFを求めるようにしてもよい。その際のマップとしては、例えば、図3に示すように、機関回転数Neが高く且つ負荷率KLが高くなるほど未燃燃料成分量ΣFが多くなるマップを例示することができる。   Further, since the fuel injection amount of the internal combustion engine 1 is determined based on the engine speed Ne and the load factor KL, the unburned fuel component amount ΣF is obtained from a map using the engine speed Ne and the load factor KL as parameters. It may be. As a map at that time, for example, as shown in FIG. 3, a map in which the unburned fuel component amount ΣF increases as the engine speed Ne increases and the load factor KL increases can be exemplified.

ここで図2に戻り、ECU16は、S103において第1気筒群2から排出される未燃燃料成分の総量ΣFを算出すると、S104へ進む。S104では、ECU16は、第1気筒群2から排出された未燃燃料成分量ΣFのうち、第1サブ触媒12において酸素(O)や窒素酸化物(NO)と反応する未燃燃料成分量Frを演算する。 Returning to FIG. 2, when the ECU 16 calculates the total amount ΣF of unburned fuel components discharged from the first cylinder group 2 in S103, the process proceeds to S104. In S104, the ECU 16 of the unburned fuel component amount ΣF discharged from the first cylinder group 2 reacts with oxygen (O 2 ) and nitrogen oxide (NO x ) in the first sub-catalyst 12. The amount Fr is calculated.

第1サブ触媒12において酸素(O)や窒素酸化物(NO)と反応する未燃燃料成分量Frは、以下の式(2)に基づいて算出することができる。
Fr=ΣF・(R1-Th1)・・・(2)
The unburned fuel component amount Fr that reacts with oxygen (O 2 ) or nitrogen oxide (NO x ) in the first sub-catalyst 12 can be calculated based on the following equation (2).
Fr = ΣF · (R1−Th1) (2)

式(2)において、R1は、第1サブ触媒12へ流入した未燃燃料成分のうち第1サブ触媒12において反応する未燃燃料成分量の割合(以下、「反応率R1」と称する)である。Th1は、第1サブ触媒12へ流入した未燃燃料成分のうち該第1サブ触媒12を未反応のまますり抜ける未燃燃料成分量の割合(以下、「すり抜け率Th1」と称する)である。   In Formula (2), R1 is the ratio of the amount of unburned fuel component that reacts in the first sub-catalyst 12 out of the unburned fuel component that has flowed into the first sub-catalyst 12 (hereinafter referred to as “reaction rate R1”). is there. Th1 is the ratio of the amount of unburned fuel component that flows through the first sub-catalyst 12 unreacted through the unburned fuel component that has flowed into the first sub-catalyst 12 (hereinafter referred to as “pass-through rate Th1”).

前記すり抜け率Th1は、第1サブ触媒12へ流入する排気の流量(言い換えれば、排気の流速)をパラメータとして求めることができる。すなわち、前記すり抜け率Th1は、第1サブ触媒12へ流入する排気の流量が増加するほど高くなり且つ第1サブ触媒12へ流入する排気の流量が減少するほど小さくなる。   The slip-through rate Th1 can be obtained using the flow rate of exhaust gas flowing into the first sub-catalyst 12 (in other words, the exhaust gas flow rate) as a parameter. That is, the slip-through rate Th1 increases as the flow rate of the exhaust gas flowing into the first sub catalyst 12 increases, and decreases as the flow rate of the exhaust gas flowing into the first sub catalyst 12 decreases.

そこで、本実施例では、前記すり抜け率Thと第1サブ触媒12へ流入する排気の流量
との関係を予め実験的に求めておくとともに、それらの関係をマップ化しておくようにした。尚、第1サブ触媒12へ流入する排気の流量としては、第1気筒群2の総吸入空気量Gat1を用いることができる。
Therefore, in this embodiment, the relationship between the slip-through rate Th and the flow rate of the exhaust gas flowing into the first sub-catalyst 12 is obtained experimentally in advance, and the relationship is mapped. The total intake air amount Gat1 of the first cylinder group 2 can be used as the flow rate of the exhaust gas flowing into the first sub catalyst 12.

次に、式(2)における反応率R1は、第1サブ触媒12の床温に相関する反応率Rt1と第1サブ触媒12へ流入する排気の空燃比に相関する反応率Raf1との乗算値である。   Next, the reaction rate R1 in the equation (2) is a product of the reaction rate Rt1 correlated with the bed temperature of the first sub-catalyst 12 and the reaction rate Raf1 correlated with the air-fuel ratio of the exhaust gas flowing into the first sub-catalyst 12. It is.

前記反応率Raf1は、図4に示すように、第1サブ触媒12へ流入する排気の空燃比が一定の空燃比(例えば、理論空燃比より若干高い空燃比)より低い場合は、排気の空燃比が高くなるほど高くなり、排気の空燃比が前記一定の空燃比を超えると略一定若しくは緩やかに低下する傾向を有している。本実施例では、図4に示すような排気の空燃比と反応率Raf1との関係を予め実験的に求めておくとともに、それらの関係をマップ化しておくようにした。   As shown in FIG. 4, when the air-fuel ratio of the exhaust gas flowing into the first sub-catalyst 12 is lower than a certain air-fuel ratio (for example, an air-fuel ratio slightly higher than the stoichiometric air-fuel ratio), the reaction rate Raf1 The higher the fuel ratio, the higher the fuel ratio. When the air / fuel ratio of the exhaust gas exceeds the certain air / fuel ratio, there is a tendency to decrease substantially constant or gently. In the present embodiment, the relationship between the air-fuel ratio of the exhaust and the reaction rate Raf1 as shown in FIG. 4 is experimentally obtained in advance, and the relationship is mapped.

前記反応率Raf1を求める際のパラメータとして用いられる排気の空燃比としては、前述したA/Frを用いることができる。   As the air-fuel ratio of exhaust used as a parameter for obtaining the reaction rate Raf1, the above-described A / Fr can be used.

また、前記反応率Rt1は、図5に示すように、第1サブ触媒12の床温Tcat1が一定温度以下の場合は床温が高くなるほど多くなり、床温Tcat1が一定温度を超えると略一定となる傾向を有している。依って、本実施例では、図5に示すような床温Tcat1と反応率Rt1との関係を予め実験的に求めておくとともに、それらの関係をマップ化しておくようにした。   Further, as shown in FIG. 5, the reaction rate Rt1 increases as the bed temperature increases when the bed temperature Tcat1 of the first sub-catalyst 12 is equal to or lower than a certain temperature, and is substantially constant when the bed temperature Tcat1 exceeds a certain temperature. Tend to be. Therefore, in this example, the relationship between the bed temperature Tcat1 and the reaction rate Rt1 as shown in FIG. 5 was obtained experimentally in advance, and the relationship was mapped.

前記反応率Rt1を求める際のパラメータとして用いられる第1サブ触媒12の床温Tcat1は、以下の式(3)により求められる。
Tcat1=(Ehc1+Eex1+Ecat1)/(Ccat1+Cex1)・・・(3)
The bed temperature Tcat1 of the first sub-catalyst 12 used as a parameter when obtaining the reaction rate Rt1 is obtained by the following equation (3).
Tcat1 = (Ehc1 + Eex1 + Ecat1) / (Ccat1 + Cex1) (3)

式(3)において、Ehc1は第1サブ触媒12で反応する未燃燃料成分の発熱エネルギ、Eex1は第1サブ触媒12へ流入する排気が持つ熱エネルギ、Ecat1は第1サブ触媒12が持つ熱エネルギ、Ccat1は第1サブ触媒12の熱容量、Cex1は第1サブ触媒12へ流入する排気の熱容量を各々示している。   In equation (3), Ehc1 is the heat energy of the unburned fuel component that reacts with the first sub catalyst 12, Eex1 is the heat energy of the exhaust gas flowing into the first sub catalyst 12, and Ecat1 is the heat of the first sub catalyst 12. Energy, Ccat1 indicates the heat capacity of the first sub catalyst 12, and Cex1 indicates the heat capacity of the exhaust gas flowing into the first sub catalyst 12.

第1サブ触媒12で反応する未燃燃料成分の発熱エネルギEhcは、以下の式(4)により求めることができる。
Ehc1=ΣF・(R1−Th1)×Jhc・・・(4)
The exothermic energy Ehc of the unburned fuel component that reacts with the first sub-catalyst 12 can be obtained by the following equation (4).
Ehc1 = ΣF · (R1-Th1) × Jhc (4)

式(4)における反応率R1としては、本ルーチンの前回実行時に求められた値が用いられる。すり抜け率Th1としては、式(2)と同様の値が用いられる。Jhcは、単位質量当たりの未燃燃料成分(HC)の発熱エネルギ量である。   As the reaction rate R1 in the equation (4), the value obtained at the previous execution of this routine is used. As the slip-through rate Th1, a value similar to that in the expression (2) is used. Jhc is the amount of heat generated by the unburned fuel component (HC) per unit mass.

第1サブ触媒12へ流入する排気が持つ熱エネルギEex1は、第1サブ触媒12へ流入する排気の温度と、第1サブ触媒12へ流入する排気の流量(第1気筒群2の総吸入空気量Gat1)と、排気の比熱(定数)とを乗算することにより求めることができる。尚、第1サブ触媒12へ流入する排気の温度は、第1サブ触媒12より上流の第1排気枝管8に排気温度センサを取り付けて実測することが好ましい。   The thermal energy Eex1 possessed by the exhaust gas flowing into the first sub-catalyst 12 includes the temperature of the exhaust gas flowing into the first sub-catalyst 12 and the flow rate of the exhaust gas flowing into the first sub-catalyst 12 (total intake air of the first cylinder group 2). It can be obtained by multiplying the amount Gat1) by the specific heat (constant) of the exhaust. The temperature of the exhaust gas flowing into the first sub catalyst 12 is preferably measured by attaching an exhaust temperature sensor to the first exhaust branch pipe 8 upstream of the first sub catalyst 12.

第1サブ触媒12が持つ熱エネルギEcat1は、第1サブ触媒12の床温と第1サブ触媒12の熱容量Ccat1とを乗算することにより求めることができる。その際、第1
サブ触媒12の床温は、本ルーチンの前回実行時に算出された床温である。
The thermal energy Ecat1 of the first sub-catalyst 12 can be obtained by multiplying the bed temperature of the first sub-catalyst 12 and the heat capacity Ccat1 of the first sub-catalyst 12. At that time, the first
The bed temperature of the sub-catalyst 12 is the bed temperature calculated at the previous execution of this routine.

第1サブ触媒12へ流入する排気の熱容量Cex1は、第1サブ触媒12へ流入する排気の流量(第1気筒群2の総吸入空気量Gat1)と排気の比熱(定数)とを乗算することにより求めることができる。   The heat capacity Cex1 of the exhaust gas flowing into the first sub catalyst 12 is multiplied by the flow rate of the exhaust gas flowing into the first sub catalyst 12 (total intake air amount Gat1 of the first cylinder group 2) and the specific heat (constant) of the exhaust gas. It can ask for.

このようにして第1サブ触媒12において酸素(O)や窒素酸化物(NO)と反応する未燃燃料成分量Frが求められると、ECU16は、図2のS105へ進む。S105では、メイン触媒11へ供給される未燃燃料成分量Fmを演算する。 When the unburned fuel component amount Fr that reacts with oxygen (O 2 ) or nitrogen oxide (NO x ) in the first sub-catalyst 12 is obtained in this way, the ECU 16 proceeds to S105 in FIG. In S105, the unburned fuel component amount Fm supplied to the main catalyst 11 is calculated.

具体的には、ECU16は、前記S103で算出された未燃燃料成分量ΣFから前記S104で算出された未燃燃料成分量Frを減算することにより、メイン触媒11へ供給される未燃燃料成分量Fm(=ΣF−Fr=ΣF・(1−R1+Th1))を算出する。   Specifically, the ECU 16 subtracts the unburned fuel component amount Fr calculated in S104 from the unburned fuel component amount ΣF calculated in S103, so that the unburned fuel component supplied to the main catalyst 11 is subtracted. The amount Fm (= ΣF−Fr = ΣF · (1−R1 + Th1)) is calculated.

S106では、ECU16は、前記S105で算出された未燃燃料成分量(メイン触媒11へ供給される未燃燃料成分量)Fmに基づいてメイン触媒11の床温Tcat2を演算する。   In S106, the ECU 16 calculates the bed temperature Tcat2 of the main catalyst 11 based on the unburned fuel component amount (unburned fuel component amount supplied to the main catalyst 11) Fm calculated in S105.

具体的には、ECU16は、第1サブ触媒12の床温Tcat1と同様の方法によりメイン触媒11の床温Tcat2を演算する。すなわち、ECU16は、以下の式(5)に基づいてメイン触媒11の床温Tcat2を演算する。
Tcat2=(Ehc2+Eex2+Ecat2)/(Ccat2+Cex2)・・・(5)
Specifically, the ECU 16 calculates the bed temperature Tcat2 of the main catalyst 11 by the same method as the bed temperature Tcat1 of the first sub catalyst 12. That is, the ECU 16 calculates the bed temperature Tcat2 of the main catalyst 11 based on the following equation (5).
Tcat2 = (Ehc2 + Eex2 + Ecat2) / (Ccat2 + Cex2) (5)

上記した式(5)は、前述した式(3)において、Ehc1をメイン触媒11で反応する未燃燃料成分の発熱エネルギEhc2、Eex1をメイン触媒11へ流入する排気が持つ熱エネルギEex2、Ecat1をメイン触媒11が持つ熱エネルギEcat2、Ccat1をメイン触媒11の熱容量Ccat2、Cex1をメイン触媒11へ流入する排気の熱容量Cex2に各々置き換えた式である。   Formula (5) described above is the above-described formula (3). The heat energy Ehc2 of the unburned fuel component that reacts Ehc1 with the main catalyst 11 and the heat energy Eex2 and Ecat1 of the exhaust gas flowing into the main catalyst 11 from Eex1 are expressed as follows. This is an equation in which the thermal energy Ecat2 and Ccat1 of the main catalyst 11 is replaced with the heat capacity Ccat2 of the main catalyst 11 and the heat capacity Cex2 of the exhaust gas flowing into the main catalyst 11 respectively.

メイン触媒11で反応する未燃燃料成分の発熱エネルギEhc2は、以下の式(6)により求めることができる。
Ehc2=Fm・(R2−Th2)×Jhc・・・(6)
The exothermic energy Ehc2 of the unburned fuel component that reacts with the main catalyst 11 can be obtained by the following equation (6).
Ehc2 = Fm · (R2-Th2) × Jhc (6)

式(6)における反応率R2は、前述した第1サブ触媒12における反応率R1と同様に、メイン触媒11の床温Tcat2(本ルーチンの前回実行時に算出された床温)と、メイン触媒11へ流入する排気の空燃比(空燃比センサ15の測定値A/F)とをパラメータとして求められる。   The reaction rate R2 in the equation (6) is the same as the reaction rate R1 in the first sub-catalyst 12 described above, the bed temperature Tcat2 of the main catalyst 11 (the bed temperature calculated at the previous execution of this routine), the main catalyst 11 The air-fuel ratio of the exhaust gas flowing into the engine (measured value A / F of the air-fuel ratio sensor 15) is obtained as a parameter.

式(6)におけるすり抜け率Th2は、前述した第1サブ触媒12のすり抜け率Th1と同様に、メイン触媒11へ流入する排気の流量(エアフローメータ7の測定値Ga)をパラメータとして求められる。   The slip-through rate Th2 in equation (6) is obtained using the flow rate of exhaust gas flowing into the main catalyst 11 (measured value Ga of the air flow meter 7) as a parameter, similarly to the slip-through rate Th1 of the first sub-catalyst 12 described above.

メイン触媒11へ流入する排気が持つ熱エネルギEex2は、メイン触媒11へ流入する排気の温度(排気温度センサ14の測定値)と、メイン触媒11へ流入する排気の流量(エアフローメータ7の測定値Ga)と、排気の比熱(定数)を乗算することにより求めることができる。   The heat energy Eex2 of the exhaust gas flowing into the main catalyst 11 includes the temperature of the exhaust gas flowing into the main catalyst 11 (measured value of the exhaust temperature sensor 14) and the flow rate of exhaust gas flowing into the main catalyst 11 (measured value of the air flow meter 7). It can be obtained by multiplying Ga) by the specific heat (constant) of the exhaust.

メイン触媒11が持つ熱エネルギEcat2は、メイン触媒11の床温(本ルーチンの前回実行時に算出された床温)とメイン触媒11の熱容量Ccat2とを乗算することに
より求めることができる。
The thermal energy Ecat2 of the main catalyst 11 can be obtained by multiplying the bed temperature of the main catalyst 11 (bed temperature calculated at the previous execution of this routine) and the heat capacity Ccat2 of the main catalyst 11.

メイン触媒11へ流入する排気の熱容量Cex2は、メイン触媒11へ流入する排気の流量(エアフローメータ7の測定値Ga)と排気の比熱(定数)とを乗算することにより求めることができる。   The heat capacity Cex2 of the exhaust gas flowing into the main catalyst 11 can be obtained by multiplying the flow rate of the exhaust gas flowing into the main catalyst 11 (measured value Ga of the air flow meter 7) and the specific heat (constant) of the exhaust gas.

以上述べたようにECU16が図2の温度推定ルーチンを実行することにより、本発明に係る推定手段が実現される。依って、ECU16が図2の温度推定ルーチンに基づいて推定したメイン触媒11の床温Tcat2は、メイン触媒11へ供給される未燃燃料成分量が正確に反映された温度となる。その結果、メイン触媒11の床温が正確に推定されるようになる。   As described above, when the ECU 16 executes the temperature estimation routine of FIG. 2, the estimation means according to the present invention is realized. Therefore, the bed temperature Tcat2 of the main catalyst 11 estimated by the ECU 16 based on the temperature estimation routine of FIG. 2 is a temperature that accurately reflects the amount of unburned fuel component supplied to the main catalyst 11. As a result, the bed temperature of the main catalyst 11 can be accurately estimated.

メイン触媒11の床温が正確に推定されると、メイン触媒11の床温が温度浄化ウィンドに収まるように空燃比独立制御を行うことが可能となる。その結果、メイン触媒11の温度が温度浄化ウィンドから外れ、或いはメイン触媒11が過昇温する等の不具合を払拭することができる。   When the bed temperature of the main catalyst 11 is accurately estimated, the air-fuel ratio independent control can be performed so that the bed temperature of the main catalyst 11 falls within the temperature purification window. As a result, it is possible to eliminate problems such as the temperature of the main catalyst 11 deviating from the temperature purification window or the main catalyst 11 overheating.

例えば、ECU16は、推定されたメイン触媒11の床温が温度浄化ウィンドより低くなった場合には、第1気筒群2の空燃比を低下(リッチ側へ補正)させるとともに第2気筒群3の空燃比を上昇(リーン側へ補正)するようにしてもよい。この場合、第1気筒群2から排出される未燃燃料成分量と第2気筒群3から排出される酸素量が増加する。その結果、メイン触媒11において未燃燃料成分と酸素(O)が反応する際に発生する熱量が増加し、メイン触媒11の床温が高められる。 For example, when the estimated bed temperature of the main catalyst 11 becomes lower than the temperature purification window, the ECU 16 reduces the air-fuel ratio of the first cylinder group 2 (corrects to the rich side) and The air-fuel ratio may be increased (corrected to the lean side). In this case, the amount of unburned fuel components discharged from the first cylinder group 2 and the amount of oxygen discharged from the second cylinder group 3 increase. As a result, the amount of heat generated when the unburned fuel component reacts with oxygen (O 2 ) in the main catalyst 11 increases, and the bed temperature of the main catalyst 11 is increased.

一方、推定されたメイン触媒11の床温が温度浄化ウィンドより高くなった場合には、ECU16は、第1気筒群2の空燃比を上昇(リーン側へ補正)させるとともに第2気筒群3の空燃比を低下(リッチ側へ補正)するようにしてもよい。この場合、第1気筒群2から排出される未燃燃料成分量と第2気筒群3から排出される酸素量が減少する。その結果、メイン触媒11において未燃燃料成分と酸素(O)が反応する際に発生する熱量が減少し、メイン触媒11の床温が低下する。 On the other hand, when the estimated bed temperature of the main catalyst 11 becomes higher than the temperature purification window, the ECU 16 increases (corrects to the lean side) the air-fuel ratio of the first cylinder group 2 and The air-fuel ratio may be lowered (corrected to the rich side). In this case, the unburned fuel component amount discharged from the first cylinder group 2 and the oxygen amount discharged from the second cylinder group 3 are reduced. As a result, the amount of heat generated when the unburned fuel component reacts with oxygen (O 2 ) in the main catalyst 11 decreases, and the bed temperature of the main catalyst 11 decreases.

尚、本実施例では、第1サブ触媒12及びメイン触媒11の床温を求める際に、走行風による放熱性の変動や点火時期による排気温度の変動などを考慮していないが、必要に応じてそれらのパラメータを考慮するようにしてもよい。走行風による放熱性は、外気温度や車両の走行速度と相関するため、それらをパラメータとして特定されるようにしてもよい。   In this embodiment, when obtaining the bed temperatures of the first sub-catalyst 12 and the main catalyst 11, no consideration is given to fluctuations in heat dissipation due to running wind, fluctuations in exhaust temperature due to ignition timing, etc. These parameters may be taken into consideration. Since the heat dissipation by the traveling wind correlates with the outside air temperature and the traveling speed of the vehicle, they may be specified as parameters.

本発明を適用する内燃機関の概略構成を示す図である。1 is a diagram showing a schematic configuration of an internal combustion engine to which the present invention is applied. 本実施例における温度推定ルーチンを示すフローチャートである。It is a flowchart which shows the temperature estimation routine in a present Example. リッチ空燃比で運転される気筒群から排出される未燃燃料成分量ΣFと機関回転数Neと負荷率KLとの関係を示す図である。It is a figure which shows the relationship between the unburned fuel component amount (SIGMA) F discharged | emitted from the cylinder group drive | operated by a rich air fuel ratio, the engine speed Ne, and the load factor KL. 第1サブ触媒へ流入する排気の空燃比A/Frと第1サブ触媒における未燃燃料成分の反応率Raf1との関係を示す図である。It is a figure which shows the relationship between the air fuel ratio A / Fr of the exhaust_gas | exhaustion which flows into a 1st subcatalyst, and the reaction rate Raf1 of the unburned fuel component in a 1st subcatalyst. 第1サブ触媒の床温Tcat1と第1サブ触媒における未燃燃料成分の反応率Rt1との関係を示す図である。It is a figure which shows the relationship between the bed temperature Tcat1 of a 1st subcatalyst, and the reaction rate Rt1 of the unburned fuel component in a 1st subcatalyst.

符号の説明Explanation of symbols

1・・・・・内燃機関
2・・・・・第1気筒群
3・・・・・第2気筒群
4・・・・・気筒
5・・・・・燃料噴射弁
7・・・・・エアフローメータ
8・・・・・第1排気枝管
9・・・・・第2排気枝管
10・・・・排気管(合流排気管)
11・・・・メイン触媒(第1触媒)
12・・・・第1サブ触媒(第2触媒)
14・・・・排気温度センサ
15・・・・空燃比センサ
16・・・・ECU(制御手段、推定手段)
DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... 1st cylinder group 3 ... 2nd cylinder group 4 ... Cylinder 5 ... Fuel injection valve 7 ... Air flow meter 8 ... 1st exhaust branch pipe 9 ... 2nd exhaust branch pipe 10 ... ... Exhaust pipe (joint exhaust pipe)
11 .... Main catalyst (first catalyst)
12 .... first sub-catalyst (second catalyst)
14 .... Exhaust temperature sensor 15 .... Air-fuel ratio sensor 16 .... ECU (control means, estimation means)

Claims (3)

内燃機関の複数の気筒群に各々接続された複数の排気枝管と、
前記複数の排気枝管を合流させた合流排気管と、
前記合流排気管に配置された第1触媒と、
前記複数の気筒群の一部をリッチ空燃比で運転させるとともに残余の気筒群をリーン空燃比で運転させる空燃比独立制御を行う制御手段と、
前記複数の排気枝管のうち、前記空燃比独立制御の実行時にリッチ空燃比で運転させられる気筒群の排気枝管に配置された第2触媒と、
前記空燃比独立制御の実行時に前記第2触媒で反応する未燃燃料成分量に基づいて前記第1触媒の温度を推定する推定手段と、
を備えることを特徴とする内燃機関の触媒温度推定装置。
A plurality of exhaust branch pipes respectively connected to a plurality of cylinder groups of the internal combustion engine;
A combined exhaust pipe obtained by joining the plurality of exhaust branch pipes;
A first catalyst disposed in the combined exhaust pipe;
Control means for performing air-fuel ratio independent control for operating a part of the plurality of cylinder groups at a rich air-fuel ratio and operating the remaining cylinder groups at a lean air-fuel ratio;
A second catalyst disposed in an exhaust branch pipe of a cylinder group that is operated at a rich air-fuel ratio among the plurality of exhaust branch pipes when the air-fuel ratio independent control is performed;
Estimating means for estimating the temperature of the first catalyst based on the amount of unburned fuel component that reacts with the second catalyst when the air-fuel ratio independent control is performed;
A catalyst temperature estimation device for an internal combustion engine, comprising:
請求項1において、前記推定手段は、前記空燃比独立制御の実行時にリッチ空燃比で運転される気筒群から排出される未燃燃料成分量を演算し、算出された未燃燃料成分量から前記第2触媒で反応する未燃燃料成分量を減算して前記第1触媒へ流入する未燃燃料成分量を算出し、前記第1触媒へ流入する未燃燃料成分量のうち該第1触媒で反応する未燃燃料成分量を算出し、前記第1触媒で反応する未燃燃料成分量から前記第1触媒の温度を推定することを特徴とする内燃機関の触媒温度推定装置。 In Claim 1, the said estimation means calculates the amount of unburned fuel components discharged | emitted from the cylinder group operated by a rich air fuel ratio at the time of execution of the said air fuel ratio independent control, and the said amount of unburned fuel component is calculated from the calculated amount of unburned fuel components The amount of unburned fuel component that reacts with the second catalyst is subtracted to calculate the amount of unburned fuel component that flows into the first catalyst, and the first catalyst out of the amount of unburned fuel component that flows into the first catalyst. A catalyst temperature estimation device for an internal combustion engine, wherein an amount of unburned fuel component that reacts is calculated, and a temperature of the first catalyst is estimated from the amount of unburned fuel component that reacts with the first catalyst. 請求項1又は2において、前記推定手段は、前記第2触媒へ流入する排気の空燃比、排気流量、及び前記第2触媒の温度に基づいて、前記第2触媒で反応する未燃燃料成分量を特定することを特徴とする内燃機関の触媒温度推定装置。
3. The unburned fuel component amount that reacts in the second catalyst based on the air-fuel ratio of the exhaust gas flowing into the second catalyst, the exhaust gas flow rate, and the temperature of the second catalyst. A catalyst temperature estimation device for an internal combustion engine characterized by:
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