JP4998341B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Exhaust gas purification device for internal combustion engine Download PDF

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JP4998341B2
JP4998341B2 JP2008065695A JP2008065695A JP4998341B2 JP 4998341 B2 JP4998341 B2 JP 4998341B2 JP 2008065695 A JP2008065695 A JP 2008065695A JP 2008065695 A JP2008065695 A JP 2008065695A JP 4998341 B2 JP4998341 B2 JP 4998341B2
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俊博 森
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Toyota Motor Corp
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Description

本発明は、上流触媒及び下流触媒が排気通路上に直列に配置された内燃機関の排気浄化装置に関する。   The present invention relates to an exhaust purification device for an internal combustion engine in which an upstream catalyst and a downstream catalyst are arranged in series on an exhaust passage.

この種の技術が、例えば特許文献１に記載されている。特許文献１には、下流触媒の前後に排気温センサを設けて、下流触媒前後の排気温の差に基づいて下流触媒でのＨＣ反応量を推定することによって、上流触媒へのＨＣ供給量を制御する技術が提案されている。具体的には、下流触媒でのＨＣ反応量（ＨＣ供給量）が不足している場合には、上流からのＨＣ供給量を増量する制御を行っている。こうすることで、上流触媒及び下流触媒に対する過不足のないＨＣの供給を図っている。   This type of technique is described in Patent Document 1, for example. In Patent Document 1, exhaust temperature sensors are provided before and after the downstream catalyst, and the amount of HC supplied to the upstream catalyst is estimated by estimating the amount of HC reaction at the downstream catalyst based on the difference in exhaust temperature before and after the downstream catalyst. Control techniques have been proposed. Specifically, when the amount of HC reaction (HC supply amount) in the downstream catalyst is insufficient, control is performed to increase the amount of HC supply from the upstream. By doing so, the supply of HC without excess or deficiency to the upstream catalyst and the downstream catalyst is attempted.

特開平１１−３５０９３９号公報JP 11-350939 A

しかしながら、上記した特許文献１に記載された技術では、精度良く制御を行うために、下流触媒前後の排気温を取得するための２つの温度センサを用いる必要があった。そのため、コストアップしてしまう場合があった。   However, in the technique described in Patent Document 1 described above, it is necessary to use two temperature sensors for acquiring exhaust gas temperatures before and after the downstream catalyst in order to perform control with high accuracy. As a result, the cost may increase.

本発明は、上記のような課題を解決するためになされたものであり、１つの温度センサのみを用いて、下流触媒の温度を精度よく推定可能な内燃機関の排気浄化装置を提供することを目的とする。   The present invention has been made to solve the above problems, and provides an exhaust purification device for an internal combustion engine that can accurately estimate the temperature of a downstream catalyst using only one temperature sensor. Objective.

本発明の１つの観点では、排気通路上に設けられた第１の触媒と、前記排気通路上における前記第１の触媒の下流側に設けられた第２の触媒と、を備えた内燃機関の排気浄化装置は、前記第１の触媒からのすり抜けＨＣ量を推定するすり抜けＨＣ量推定手段と、前記すり抜けＨＣ量に基づいてすり抜けＨＣによる前記第２の触媒の発熱を求め、当該発熱に基づいて前記第２の触媒の温度を推定する第２の触媒温度推定手段と、を備え、前記すり抜けＨＣ量推定手段は、前記第１の触媒への入りガス温度及び前記第２の触媒の目標温度に基づいて前記第１の触媒及び前記第２の触媒へのＨＣ供給量を規定すると共に、前記入りガス温度及び前記第１の触媒の温度に基づいて前記第１の触媒におけるＨＣ反応量を規定し、前記ＨＣ供給量に対する前記ＨＣ反応量の割合を求め、前記割合に基づいて前記すり抜けＨＣ量を推定する。
In one aspect of the present invention, an internal combustion engine comprising: a first catalyst provided on an exhaust passage; and a second catalyst provided on the exhaust passage downstream of the first catalyst. The exhaust emission control device obtains a passing-through HC amount estimating means for estimating a slipping-off HC amount from the first catalyst, and calculates heat generation of the second catalyst due to the passing-through HC based on the passing-through HC amount, and based on the generated heat Second catalyst temperature estimating means for estimating the temperature of the second catalyst, and the slip-through HC amount estimating means is configured to set the temperature of the gas entering the first catalyst and the target temperature of the second catalyst. Based on this, the amount of HC supplied to the first catalyst and the second catalyst is defined, and the amount of HC reaction in the first catalyst is defined based on the inlet gas temperature and the temperature of the first catalyst. , Against the HC supply amount Obtains the ratio of the serial HC reaction volume, the slipping estimates the HC amount based on the ratio.

上記の内燃機関の排気浄化装置は、排気通路上に直列に配置された第１の触媒（上流触媒）及び第２の触媒（下流触媒）を用いて、内燃機関から排出された排気ガスを浄化するために好適に利用される。すり抜けＨＣ量推定手段は、第１の触媒からすり抜けたＨＣ量を推定し、第２の触媒温度推定手段は、第１の触媒からすり抜けたＨＣによる第２の触媒の発熱を考慮して第２の触媒温度を推定する。これにより、第２の触媒における前後の排気温を用いずに（例えば、第２の触媒前後の排気温を取得するための２つの温度センサを用いずに）、第２の触媒の温度を精度良く推定することが可能となる。
具体的には、すり抜けＨＣ量推定手段は、第１の触媒への入りガス温度及び第２の触媒の目標温度に基づいて第１の触媒及び第２の触媒へのＨＣ供給量を規定すると共に、第１の触媒への入りガス温度及び第１の触媒の温度に基づいて第１の触媒におけるＨＣ反応量を規定し、ＨＣ供給量に対するＨＣ反応量に基づいてすり抜けＨＣ量を推定する。これにより、すり抜けＨＣ量を精度良く推定することができる。
The exhaust gas purification apparatus for an internal combustion engine purifies exhaust gas discharged from the internal combustion engine using a first catalyst (upstream catalyst) and a second catalyst (downstream catalyst) arranged in series on the exhaust passage. It is preferably used for this purpose. The slip-through HC amount estimation means estimates the amount of HC slipped from the first catalyst, and the second catalyst temperature estimation means takes into account the second catalyst heat generated by the HC slipping from the first catalyst. Estimate the catalyst temperature. Accordingly, the temperature of the second catalyst is accurately determined without using the exhaust temperatures before and after the second catalyst (for example, without using two temperature sensors for acquiring the exhaust temperatures before and after the second catalyst). It is possible to estimate well.
Specifically, the slip-through HC amount estimation means defines the HC supply amount to the first catalyst and the second catalyst based on the temperature of the gas entering the first catalyst and the target temperature of the second catalyst. The amount of HC reaction in the first catalyst is defined based on the temperature of the gas entering the first catalyst and the temperature of the first catalyst, and the slip-through HC amount is estimated based on the amount of HC reaction relative to the amount of HC supplied. Thereby, it is possible to accurately estimate the slip-through HC amount.

上記の内燃機関の排気浄化装置において好適には、前記第１の触媒と前記第２の触媒との間を通過する排気ガスの温度を取得する排気ガス温度取得手段を更に備え、前記第２の触媒温度推定手段は、前記すり抜けＨＣによる前記第２の触媒の発熱を含む前記第２の触媒の発熱量と放熱量との差に対応する温度を、前記排気ガス温度取得手段によって取得された排気ガスの温度に加算することによって、前記第２の触媒の温度を求める。これにより、第１の触媒と第２の触媒との間の排気温のみを取得することで（例えば１つの温度センサのみを用いることで）、第２の触媒の温度を精度良く推定することが可能となる。   Preferably, the exhaust gas purification apparatus for an internal combustion engine further includes exhaust gas temperature acquisition means for acquiring a temperature of exhaust gas passing between the first catalyst and the second catalyst, The catalyst temperature estimating means is an exhaust gas temperature acquired by the exhaust gas temperature acquiring means, corresponding to a difference between the heat value of the second catalyst including the heat generation of the second catalyst due to the slip-through HC and the heat radiation amount. The temperature of the second catalyst is obtained by adding to the temperature of the gas. Thereby, by acquiring only the exhaust temperature between the first catalyst and the second catalyst (for example, by using only one temperature sensor), the temperature of the second catalyst can be accurately estimated. It becomes possible.

以下、図面を参照して本発明の好適な実施の形態について説明する。   Preferred embodiments of the present invention will be described below with reference to the drawings.

［全体構成］
図１は、本実施形態に係る内燃機関の排気浄化装置１０の概略構成図を示す。図１では、実線矢印が排気ガスの流れを示し、破線矢印が信号の入出力を示している。 [overall structure]
FIG. 1 is a schematic configuration diagram of an exhaust purification device 10 for an internal combustion engine according to the present embodiment. In FIG. 1, solid arrows indicate the flow of exhaust gas, and broken arrows indicate input / output of signals.

内燃機関の排気浄化装置１０は、主に、排気通路１と、上流触媒２と、下流触媒３と、排気温センサ４と、ＥＣＵ（Engine Control Unit）７と、を有する。内燃機関の排気浄化装置１０は、車両に搭載され、内燃機関（ガソリンエンジンやディーゼルエンジン）から排出された排気ガスを浄化するために利用される。   An exhaust purification device 10 for an internal combustion engine mainly includes an exhaust passage 1, an upstream catalyst 2, a downstream catalyst 3, an exhaust temperature sensor 4, and an ECU (Engine Control Unit) 7. An exhaust gas purification device 10 for an internal combustion engine is mounted on a vehicle and used to purify exhaust gas discharged from an internal combustion engine (a gasoline engine or a diesel engine).

上流触媒２及び下流触媒３は、排気ガス中のＮＯｘやＳＯｘなどを浄化可能に構成されている。例えば、上流触媒２は酸化触媒などで構成され、下流触媒３はＤＰＲ（Diesel Particulate active Reduction system）などで構成される。上流触媒２及び下流触媒３には、上流触媒２の上流側から、ＮＯｘの還元剤として燃料等のＨＣ（炭化水素）が供給される。例えば、燃料噴射弁（不図示）や排気通路１上に設けられた燃料添加弁（不図示）より燃料を添加することによって、上流触媒２及び下流触媒３へＨＣが供給される。なお、上流触媒２、下流触媒３は、それぞれ本発明における第１の触媒、第２の触媒に相当する。   The upstream catalyst 2 and the downstream catalyst 3 are configured to be able to purify NOx, SOx and the like in the exhaust gas. For example, the upstream catalyst 2 is composed of an oxidation catalyst or the like, and the downstream catalyst 3 is composed of a DPR (Diesel Particulate active Reduction system) or the like. The upstream catalyst 2 and the downstream catalyst 3 are supplied with HC (hydrocarbon) such as fuel as a NOx reducing agent from the upstream side of the upstream catalyst 2. For example, HC is supplied to the upstream catalyst 2 and the downstream catalyst 3 by adding fuel from a fuel injection valve (not shown) or a fuel addition valve (not shown) provided on the exhaust passage 1. The upstream catalyst 2 and the downstream catalyst 3 correspond to the first catalyst and the second catalyst in the present invention, respectively.

排気温センサ４は、上流触媒２と下流触媒３との間の排気通路１上に設けられており、排気ガスの温度（排気温）を検出する。当該排気温は、下流触媒３への入りガス温度に相当する。排気温センサ４は、検出した排気温に対応する検出信号をＥＣＵ７に供給する。なお、排気温センサ４は、本発明における排気ガス温度取得手段に相当する。   The exhaust temperature sensor 4 is provided on the exhaust passage 1 between the upstream catalyst 2 and the downstream catalyst 3, and detects the temperature of exhaust gas (exhaust temperature). The exhaust temperature corresponds to the temperature of the gas entering the downstream catalyst 3. The exhaust temperature sensor 4 supplies a detection signal corresponding to the detected exhaust temperature to the ECU 7. The exhaust temperature sensor 4 corresponds to the exhaust gas temperature acquisition means in the present invention.

ＥＣＵ７は、図示しないＣＰＵ（Central Processing Unit）、ＲＯＭ（Read Only Memory）及びＲＡＭ（Random Access Memory）などを備えて構成される。本実施形態においては、ＥＣＵ７は、上流触媒２からのすり抜けＨＣ量を推定するすり抜けＨＣ量推定手段、及び下流触媒３の温度を推定する第２の触媒温度推定手段として機能する。なお、ＥＣＵ７が行う処理の詳細は後述する。   The ECU 7 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like (not shown). In the present embodiment, the ECU 7 functions as a slip-through HC amount estimation means for estimating the slip-through HC amount from the upstream catalyst 2 and a second catalyst temperature estimation means for estimating the temperature of the downstream catalyst 3. Details of the processing performed by the ECU 7 will be described later.

なお、図１に示すように、以下では、上流触媒２の上流側の排気温（上流触媒２への入りガス温度）を「Ｔ１」と表記し、上流触媒２の温度を「Ｔｃ１」と表記し、上流触媒２と下流触媒３との間の排気温（排気温センサ４によって検出される温度）を「Ｔ２」と表記し、下流触媒３の温度を「Ｔｃ２」と表記する。   In the following, as shown in FIG. 1, the exhaust temperature upstream of the upstream catalyst 2 (the temperature of the gas entering the upstream catalyst 2) is expressed as “T1”, and the temperature of the upstream catalyst 2 is expressed as “Tc1”. The exhaust temperature between the upstream catalyst 2 and the downstream catalyst 3 (temperature detected by the exhaust temperature sensor 4) is expressed as “T2”, and the temperature of the downstream catalyst 3 is expressed as “Tc2”.

［下流触媒温度推定方法］
次に、本実施形態における下流触媒３の温度Ｔｃ２の推定方法について具体的に説明する。 [Downstream catalyst temperature estimation method]
Next, a method for estimating the temperature Tc2 of the downstream catalyst 3 in the present embodiment will be specifically described.

本実施形態では、ＥＣＵ７は、上流触媒２からすり抜けたＨＣによる下流触媒３の発熱を考慮して下流触媒３の温度Ｔｃ２を推定する。具体的には、ＥＣＵ７は、上流触媒２をすり抜けたＨＣ量（下流触媒３へのＨＣ供給量にも相当し、以下では「上流触媒すり抜けＨＣ量」と呼ぶ。）を推定し、当該上流触媒すり抜けＨＣ量に基づいてすり抜けＨＣによる下流触媒３の発熱を求める。この場合、ＥＣＵ７は、上流触媒２への入りガス温度Ｔ１、上流触媒２の温度Ｔｃ１、及び下流触媒３の目標温度に基づいて、上流触媒２へのＨＣ供給量に対する当該上流触媒２におけるＨＣ反応量の割合を求め、当該割合に基づいて上流触媒すり抜けＨＣ量を推定する。そして、ＥＣＵ７は、すり抜けたＨＣによる下流触媒３の発熱を含む下流触媒３の発熱量と放熱量との差に対応する温度（以下では、「ΔＴ」と表記する。）を、排気温センサ４によって検出された排気温Ｔ２に加算することによって、下流触媒３の温度Ｔｃ２を求める。   In the present embodiment, the ECU 7 estimates the temperature Tc2 of the downstream catalyst 3 in consideration of the heat generation of the downstream catalyst 3 due to the HC slipping from the upstream catalyst 2. Specifically, the ECU 7 estimates the amount of HC that has passed through the upstream catalyst 2 (which also corresponds to the amount of HC supplied to the downstream catalyst 3, hereinafter referred to as “upstream catalyst slipping HC amount”), and the upstream catalyst. The heat generation of the downstream catalyst 3 due to the slip-through HC is obtained based on the slip-through HC amount. In this case, the ECU 7 performs the HC reaction in the upstream catalyst 2 with respect to the amount of HC supplied to the upstream catalyst 2 based on the inlet gas temperature T1 to the upstream catalyst 2, the temperature Tc1 of the upstream catalyst 2, and the target temperature of the downstream catalyst 3. The ratio of the amount is obtained, and the amount of HC passing through the upstream catalyst is estimated based on the ratio. Then, the ECU 7 sets the temperature corresponding to the difference between the heat generation amount of the downstream catalyst 3 including the heat generation of the downstream catalyst 3 due to the passing through HC and the heat release amount (hereinafter referred to as “ΔT”), and the exhaust temperature sensor 4. The temperature Tc2 of the downstream catalyst 3 is obtained by adding to the exhaust gas temperature T2 detected by the above.

このように下流触媒３の温度Ｔｃ２を推定する理由は、以下の通りである。排気温センサ４が検出した排気温のみを用いて下流触媒３の温度Ｔｃ２を推定した場合、言い換えると下流触媒３の前後の排気温を取得するための２つの温度センサを用いずに排気温センサ４のみを用いて下流触媒３の温度Ｔｃ２を推定した場合、推定された温度が実際の下流触媒３の温度からずれてしまう場合がある。こうなるのは、上流触媒２からすり抜けたＨＣによる下流触媒３の発熱に起因するものと考えられる。つまり、上流触媒２からＨＣがすり抜けたことにより、下流触媒３での反応ＨＣ量が変化したためであると考えられる。   The reason for estimating the temperature Tc2 of the downstream catalyst 3 in this way is as follows. When the temperature Tc2 of the downstream catalyst 3 is estimated using only the exhaust temperature detected by the exhaust temperature sensor 4, in other words, without using the two temperature sensors for acquiring the exhaust temperatures before and after the downstream catalyst 3, the exhaust temperature sensor When the temperature Tc2 of the downstream catalyst 3 is estimated using only 4, the estimated temperature may deviate from the actual temperature of the downstream catalyst 3. This is considered to be caused by the heat generation of the downstream catalyst 3 due to the HC slipping from the upstream catalyst 2. In other words, it is considered that the amount of reaction HC in the downstream catalyst 3 has changed due to the passage of HC from the upstream catalyst 2.

したがって、本実施形態では、上流触媒２からすり抜けたＨＣによる下流触媒３の発熱を考慮して下流触媒３の温度Ｔｃ２を推定する。これにより、１つの排気温センサ４のみを用いて、下流触媒３の温度Ｔｃ２を精度良く推定することができる。   Therefore, in the present embodiment, the temperature Tc2 of the downstream catalyst 3 is estimated in consideration of the heat generation of the downstream catalyst 3 due to the HC slipping from the upstream catalyst 2. As a result, the temperature Tc2 of the downstream catalyst 3 can be accurately estimated using only one exhaust temperature sensor 4.

次に、下流触媒３の温度Ｔｃ２の推定方法について、より詳細に説明する。   Next, a method for estimating the temperature Tc2 of the downstream catalyst 3 will be described in more detail.

ＥＣＵ７は、前述した下流触媒３の温度Ｔｃ２と排気温センサ４によって検出された排気温Ｔ２との温度差ΔＴ（ΔＴ＝Ｔｃ２−Ｔ２）を算出し、算出された温度差ΔＴから下流触媒３の温度Ｔｃ２を推定する。ここで、当該温度差ΔＴは、下流触媒３における発熱量（以下、「下流触媒発熱量」と呼ぶ。）と放熱量との差に相当すると言える。したがって、ＥＣＵ７は、下流触媒発熱量及び放熱量をそれぞれ求めることで、温度差ΔＴを算出する。そして、ＥＣＵ７は、算出された温度差ΔＴを排気温センサ４によって検出された排気温Ｔ２に加算することで、下流触媒３の温度Ｔｃ２を求める。なお、放熱量とは、排気温センサ４の下流で放熱された熱量、詳しくは排気温センサ４と下流触媒３（下流触媒３内も含む）との間で放熱された熱量に相当する。   The ECU 7 calculates a temperature difference ΔT (ΔT = Tc2−T2) between the temperature Tc2 of the downstream catalyst 3 described above and the exhaust temperature T2 detected by the exhaust temperature sensor 4, and the downstream temperature of the downstream catalyst 3 is calculated from the calculated temperature difference ΔT. The temperature Tc2 is estimated. Here, it can be said that the temperature difference ΔT corresponds to a difference between a heat generation amount in the downstream catalyst 3 (hereinafter referred to as “downstream catalyst heat generation amount”) and a heat release amount. Therefore, the ECU 7 calculates the temperature difference ΔT by obtaining the downstream catalyst heat generation amount and the heat release amount, respectively. Then, the ECU 7 calculates the temperature Tc2 of the downstream catalyst 3 by adding the calculated temperature difference ΔT to the exhaust gas temperature T2 detected by the exhaust gas temperature sensor 4. The amount of heat released corresponds to the amount of heat radiated downstream of the exhaust temperature sensor 4, more specifically, the amount of heat radiated between the exhaust temperature sensor 4 and the downstream catalyst 3 (including the inside of the downstream catalyst 3).

具体的には、ＥＣＵ７は、以下の式（１）から温度差ΔＴを算出する。   Specifically, the ECU 7 calculates the temperature difference ΔT from the following equation (1).

Figure 0004998341
式（１）に示すように、温度差ΔＴ（ΔＴ＝Ｔｃ２−Ｔ２）は、下流触媒発熱量と放熱量との差に相当する温度である。具体的には、下流触媒発熱量は、上流触媒２ですり抜けたＨＣによる下流触媒３の発熱量と、ＰＭによる下流触媒３の発熱量（ＰＭ発熱量）とを加算した熱量に相当する。この場合、上流触媒２ですり抜けたＨＣによる下流触媒３の発熱量は、式（１）に示すように、上流触媒すり抜けＨＣ量、ＨＣに対する下流触媒浄化率、劣化係数、及び換算係数から求められる。つまり、当該発熱量は、上流触媒すり抜けＨＣ量（下流触媒３へのＨＣ供給量）に対する下流触媒３のＨＣ反応量に基づいて求められる。なお、式（１）中の劣化係数は、下流触媒３の劣化度合いに相当する係数であり、下流触媒３の温度の履歴などから求められる。また、ＰＭ発熱量は、下流触媒３の温度、排気流量、ＰＭの堆積量などから求められる。更に、換算係数は、ＨＣ反応量から下流触媒３の発熱量を求めるために用いられ、単位ＨＣ量当たりの下流触媒３の発熱量に相当する係数（例えば、単位は「Ｊ／ｇ」で表される。）である。なお、ＥＣＵ７は、上記のように求められた下流触媒発熱量と放熱量との差（熱量に相当する）を温度に換算することで（例えば係数を乗算することで）、下流触媒３の温度Ｔｃ２と排気温センサ４によって検出された排気温Ｔ２との温度差ΔＴを求める。
Figure 0004998341
 As shown in Expression (1), the temperature difference ΔT (ΔT = Tc2−T2) is a temperature corresponding to the difference between the downstream catalyst heat generation amount and the heat release amount. Specifically, the heat generation amount of the downstream catalyst corresponds to the heat amount obtained by adding the heat generation amount of the downstream catalyst 3 by HC passing through the upstream catalyst 2 and the heat generation amount (PM heat generation amount) of the downstream catalyst 3 by PM. In this case, the amount of heat generated by the downstream catalyst 3 due to the HC that has passed through the upstream catalyst 2 is obtained from the amount of HC that has passed through the upstream catalyst, the downstream catalyst purification rate with respect to HC, the deterioration coefficient, and the conversion coefficient, as shown in Equation (1). . That is, the heat generation amount is obtained based on the HC reaction amount of the downstream catalyst 3 with respect to the upstream catalyst slipping HC amount (HC supply amount to the downstream catalyst 3). Note that the deterioration coefficient in the equation (1) is a coefficient corresponding to the degree of deterioration of the downstream catalyst 3, and is obtained from the temperature history of the downstream catalyst 3 and the like. Further, the PM heat generation amount is obtained from the temperature of the downstream catalyst 3, the exhaust gas flow rate, the PM accumulation amount, and the like. Further, the conversion coefficient is used to obtain the calorific value of the downstream catalyst 3 from the HC reaction amount, and is a coefficient corresponding to the calorific value of the downstream catalyst 3 per unit HC amount (for example, the unit is represented by “J / g”). Is). The ECU 7 converts the difference between the downstream catalyst heat generation amount and the heat release amount (corresponding to the heat amount) obtained as described above into a temperature (for example, by multiplying by a coefficient), and thereby the temperature of the downstream catalyst 3. A temperature difference ΔT between Tc2 and the exhaust temperature T2 detected by the exhaust temperature sensor 4 is obtained.

次に、式（１）中の上流触媒すり抜けＨＣ量の求め方について、具体的に説明する。ＥＣＵ７は、上流触媒２へのＨＣ供給量に対する当該上流触媒２におけるＨＣ反応量の割合に基づいて、上流触媒すり抜けＨＣ量を推定する。具体的には、ＥＣＵ７は、以下の式（２）から上流触媒すり抜けＨＣ量を求める。   Next, how to determine the amount of HC passing through the upstream catalyst in the formula (1) will be specifically described. The ECU 7 estimates the amount of HC passing through the upstream catalyst based on the ratio of the amount of HC reaction in the upstream catalyst 2 to the amount of HC supplied to the upstream catalyst 2. Specifically, the ECU 7 determines the amount of HC passing through the upstream catalyst from the following equation (2).

Figure 0004998341
式（２）は、上流触媒２の入りガス温度Ｔ１、上流触媒２の温度Ｔｃ１、及び下流触媒３の目標温度から、ＨＣ供給量に対するＨＣ反応量の割合を演算することで、上流触媒すり抜けＨＣ量を求めることを示している。具体的には、式（２）中の「目標温度−Ｔ１」はＨＣ供給量に相当し、「Ｔｃ１−Ｔ１」はＨＣ反応量に相当する。したがって、式（２）中の「１−（Ｔｃ１−Ｔ１）／（目標温度−Ｔ１）」は、ＨＣ供給量に対する、上流触媒２で反応せずにすり抜けたＨＣ量（上流触媒すり抜けＨＣ量）の割合に相当する。更に、式（２）中の「上流触媒流入ＨＣ量」はＨＣ供給量に相当し、排気中に添加した燃料量から求めることができる。
Figure 0004998341
 Equation (2) is obtained by calculating the ratio of the HC reaction amount to the HC supply amount from the inlet gas temperature T1 of the upstream catalyst 2, the temperature Tc1 of the upstream catalyst 2, and the target temperature of the downstream catalyst 3, thereby passing through the upstream catalyst HC. Indicates that the quantity is to be calculated. Specifically, “target temperature −T1” in equation (2) corresponds to the HC supply amount, and “Tc1−T1” corresponds to the HC reaction amount. Therefore, “1- (Tc1−T1) / (target temperature−T1)” in the formula (2) is the amount of HC slipped without reacting with the upstream catalyst 2 with respect to the amount of HC supplied (the amount of HC passing through the upstream catalyst). Is equivalent to Furthermore, the “upstream catalyst inflow HC amount” in the equation (2) corresponds to the HC supply amount, and can be obtained from the amount of fuel added to the exhaust gas.

なお、上流触媒２の入りガス温度Ｔ１は、例えば、排気温センサ又は運転状態によって規定されたマップなどから取得される。また、上流触媒２の温度Ｔｃ１は、例えば、上流触媒２と下流触媒３との間の排気温Ｔ２から推定される。この場合、排気温Ｔ２によって規定された上流触媒２の放熱量のマップを予め作成し、当該マップを参照することで上流触媒２の温度Ｔｃ１を得ることができる。   The inlet gas temperature T1 of the upstream catalyst 2 is acquired from, for example, an exhaust temperature sensor or a map defined by the operating state. Further, the temperature Tc1 of the upstream catalyst 2 is estimated from the exhaust temperature T2 between the upstream catalyst 2 and the downstream catalyst 3, for example. In this case, the temperature Tc1 of the upstream catalyst 2 can be obtained by preparing a map of the heat release amount of the upstream catalyst 2 defined by the exhaust temperature T2 in advance and referring to the map.

図２は、排気流量と上流触媒２の温度Ｔｃ１と排気温Ｔ２との関係の一例を示した図である。具体的には、横軸に排気流量を示し、縦軸に上流触媒２の温度Ｔｃ１を示している。ＥＣＵ７は、このような関係を考慮に入れて、排気流量及び排気温Ｔ２から、上流触媒２の温度Ｔｃ１を推定する。   FIG. 2 is a diagram showing an example of the relationship between the exhaust flow rate, the temperature Tc1 of the upstream catalyst 2, and the exhaust temperature T2. Specifically, the horizontal axis represents the exhaust gas flow rate, and the vertical axis represents the temperature Tc1 of the upstream catalyst 2. The ECU 7 takes the above relationship into consideration and estimates the temperature Tc1 of the upstream catalyst 2 from the exhaust gas flow rate and the exhaust gas temperature T2.

次に、式（１）中の下流触媒浄化率の求め方について、具体的に説明する。ＥＣＵ７は、排気流量と排気温Ｔ２とによって規定されたマップを参照することで、下流触媒浄化率を求める。   Next, how to determine the downstream catalyst purification rate in the formula (1) will be specifically described. The ECU 7 obtains the downstream catalyst purification rate by referring to a map defined by the exhaust gas flow rate and the exhaust gas temperature T2.

図３は、下流触媒浄化率マップの一例を示している。下流触媒浄化率マップは、排気流量（横軸）と排気温Ｔ２（縦軸）とによって規定されている。図３に示すように、排気流量が大きくなるほどＨＣが反応しにくくなり（浄化率が低くなる）、排気流量が小さくなるほどＨＣが反応しやすくなる（浄化率が高くなる）。また、排気温Ｔ２が高くなるほどＨＣが反応しやすくなり（浄化率が高くなる）、排気温Ｔ２が低くなるほどＨＣが反応しにくくなる（浄化率が低くなる）。ＥＣＵ７は、排気流量及び排気温Ｔ２をセンサより取得し、下流触媒浄化率マップを参照することで、取得された排気流量及び排気温Ｔ２に対応する下流触媒浄化率を得る。なお、このようなマップは、予め測定又は解析することで作成される。   FIG. 3 shows an example of the downstream catalyst purification rate map. The downstream catalyst purification rate map is defined by the exhaust flow rate (horizontal axis) and the exhaust temperature T2 (vertical axis). As shown in FIG. 3, as the exhaust gas flow rate increases, HC becomes less likely to react (the purification rate becomes lower), and as the exhaust gas flow rate decreases, HC becomes easier to react (the purification rate becomes higher). Further, the higher the exhaust temperature T2, the easier the reaction of HC (the purification rate becomes higher), and the lower the exhaust temperature T2, the less the reaction of HC (the purification rate becomes lower). The ECU 7 acquires the exhaust flow rate and the exhaust temperature T2 from the sensor, and obtains the downstream catalyst purification rate corresponding to the acquired exhaust flow rate and the exhaust temperature T2 by referring to the downstream catalyst purification rate map. Such a map is created by measuring or analyzing in advance.

次に、式（１）中の放熱量の求め方について、具体的に説明する。ＥＣＵ７は、排気流量と排気温Ｔ２とによって規定されたマップを参照することで、放熱量を求める。   Next, how to calculate the amount of heat release in equation (1) will be described in detail. The ECU 7 obtains the heat release amount by referring to a map defined by the exhaust flow rate and the exhaust temperature T2.

図４は、放熱量のマップ一例を示している。放熱量マップは、排気流量（横軸）と排気温Ｔ２（縦軸）とによって規定されている。図４に示すように、排気流量が大きくなるほど放熱しにくくなり（放熱量が小さくなる）、排気流量が小さくなるほど放熱しやすくなる（放熱量が大きくなる）。また、排気温Ｔ２が高くなるほど放熱しやすくなり（放熱量が大きくなる）、排気温Ｔ２が低くなるほど放熱しにくくなる（放熱量が小さくなる）。ＥＣＵ７は、排気流量及び排気温Ｔ２をセンサより取得し、放熱量マップを参照することで、取得された排気流量及び排気温Ｔ２に対応する放熱量を得る。なお、このようなマップは、予め測定又は解析することで作成される。   FIG. 4 shows an example of a map of the heat radiation amount. The heat release map is defined by the exhaust flow rate (horizontal axis) and the exhaust temperature T2 (vertical axis). As shown in FIG. 4, the greater the exhaust flow rate, the more difficult it is to dissipate heat (the amount of heat release decreases), and the smaller the exhaust flow rate, the easier the heat release (the greater the amount of heat dissipation). Further, the higher the exhaust temperature T2, the easier it is to dissipate heat (a greater amount of heat dissipation), and the lower the exhaust temperature T2, the less likely to dissipate heat (the smaller the amount of heat dissipation). The ECU 7 acquires the exhaust flow rate and the exhaust temperature T2 from the sensor, and obtains the heat release amount corresponding to the acquired exhaust flow rate and the exhaust temperature T2 by referring to the heat release amount map. Such a map is created by measuring or analyzing in advance.

以上説明した下流触媒３の温度Ｔｃ２の推定方法によれば、１つの排気温センサ４のみを用いて、つまり上流触媒２と下流触媒３との間の排気温のみを取得することで、下流触媒３の温度Ｔｃ２を精度良く推定することができる。   According to the estimation method of the temperature Tc2 of the downstream catalyst 3 described above, the downstream catalyst is obtained by using only one exhaust temperature sensor 4, that is, by obtaining only the exhaust temperature between the upstream catalyst 2 and the downstream catalyst 3. 3 can be accurately estimated.

本実施形態に係る内燃機関の排気浄化装置の概略構成図を示す。1 is a schematic configuration diagram of an exhaust gas purification apparatus for an internal combustion engine according to the present embodiment. 排気流量と上流触媒の温度と排気温との関係の一例を示す。An example of the relationship between the exhaust flow rate, the temperature of the upstream catalyst, and the exhaust temperature is shown. 下流触媒浄化率マップの一例を示す。An example of a downstream catalyst purification rate map is shown. 放熱量マップの一例を示す。An example of a heat dissipation amount map is shown.

符号の説明Explanation of symbols

１ 排気通路
２ 上流触媒（第１の触媒）
３ 下流触媒（第２の触媒）
４ 排気温センサ
７ ＥＣＵ
１０ 内燃機関の排気浄化装置 1 Exhaust passage 2 Upstream catalyst (first catalyst)
3 Downstream catalyst (second catalyst)
4 Exhaust temperature sensor 7 ECU
10 Exhaust gas purification device for internal combustion engine

Claims (2)

排気通路上に設けられた第１の触媒と、前記排気通路上における前記第１の触媒の下流側に設けられた第２の触媒と、を備えた内燃機関の排気浄化装置であって、
前記第１の触媒からのすり抜けＨＣ量を推定するすり抜けＨＣ量推定手段と、
前記すり抜けＨＣ量に基づいてすり抜けＨＣによる前記第２の触媒の発熱を求め、当該発熱に基づいて前記第２の触媒の温度を推定する第２の触媒温度推定手段と、を備え、
前記すり抜けＨＣ量推定手段は、前記第１の触媒への入りガス温度及び前記第２の触媒の目標温度に基づいて前記第１の触媒及び前記第２の触媒へのＨＣ供給量を規定すると共に、前記入りガス温度及び前記第１の触媒の温度に基づいて前記第１の触媒におけるＨＣ反応量を規定し、前記ＨＣ供給量に対する前記ＨＣ反応量の割合を求め、前記割合に基づいて前記すり抜けＨＣ量を推定することを特徴とする内燃機関の排気浄化装置。 An exhaust emission control device for an internal combustion engine, comprising: a first catalyst provided on an exhaust passage; and a second catalyst provided on the exhaust passage downstream of the first catalyst,
Slipping HC amount estimating means for estimating the slipping HC amount from the first catalyst;
A second catalyst temperature estimating means for obtaining a heat generation of the second catalyst due to the slip-through HC based on the slip-through HC amount, and estimating a temperature of the second catalyst based on the heat generation ;
The slippage HC amount estimation means defines the HC supply amount to the first catalyst and the second catalyst based on the temperature of the gas entering the first catalyst and the target temperature of the second catalyst. Defining an HC reaction amount in the first catalyst based on the inlet gas temperature and the temperature of the first catalyst, obtaining a ratio of the HC reaction amount to the HC supply amount, and passing through the slip based on the ratio An exhaust gas purification apparatus for an internal combustion engine characterized by estimating an HC amount . 前記第１の触媒と前記第２の触媒との間を通過する排気ガスの温度を取得する排気ガス温度取得手段を更に備え、
前記第２の触媒温度推定手段は、前記すり抜けＨＣによる前記第２の触媒の発熱を含む前記第２の触媒の発熱量と放熱量との差に対応する温度を、前記排気ガス温度取得手段によって取得された排気ガスの温度に加算することによって、前記第２の触媒の温度を求める請求項１に記載の内燃機関の排気浄化装置。 Exhaust gas temperature acquisition means for acquiring the temperature of the exhaust gas passing between the first catalyst and the second catalyst;
The second catalyst temperature estimating means obtains a temperature corresponding to a difference between a heat generation amount and a heat release amount of the second catalyst including heat generation of the second catalyst by the slip-through HC by the exhaust gas temperature acquisition means. by adding to the obtained temperature of exhaust gas, the exhaust purification system of an internal combustion engine according to claim 1 for determining the temperature of the second catalyst.
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