JPH11324653A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the control rate of nitrogen oxides (NOx) and the fuel cost by feeding a prescribed quantity of HC from the uppermost stream side to catalyst arranged in series. SOLUTION: NOx exhaust quantity is calculated from an engine operating state, the temperatures of the upstream side and downstream side catalyst arranged in series are judged (steps 101-104), a basic HC feeding quantity Q1 is calculated based on the upstream side catalyst temperature and the NOx exhaust quantity, a temporary correction HC feeding quantity Q2 is calculated based on the downstream side catalytic temperature and the NOx exhaust quantity, and a correction HC feeding quantity k2 .Q2 is found by multiplying the correction HC feeding quantity Q2 by a coefficient k2 according to the upstream side catalytic temperature (step 104). The HC feeding quantity Q0 is calculated by multiplying the basic HC feeding quantity Q1 by the correction HC feeding quantity k2 .Q2 (step 106) and the HC feeding quantity Q0 is guarded by the upper limit HC feeding quantity Qmax to set the HC feeding quantity to Q0 or Qmax (steps 107-110) finally.

Description

【発明の詳細な説明】DETAILED DESCRIPTION OF THE INVENTION

【０００１】[0001]

【発明の属する技術分野】本発明は、内燃機関の排気中
に含まれる窒素酸化物（以下「ＮＯｘ」と表記する）
を、直列に配置された複数の触媒で浄化する内燃機関の
排気浄化装置に関するものである。The present invention relates to nitrogen oxides (hereinafter referred to as "NOx") contained in exhaust gas of an internal combustion engine.
For purifying exhaust gas with a plurality of catalysts arranged in series.

【０００２】[0002]

【従来の技術】近年、車両の排気ガスの浄化性能を高め
るために、内燃機関の排気管に複数の触媒を直列に配置
することが提案されている。また、ディーゼルエンジン
等の酸素過剰雰囲気の排気中でＮＯｘの浄化率を高める
には、触媒に還元剤として燃料等の炭化水素（以下「Ｈ
Ｃ」と表記する）を供給することが効果的であり、その
ため、触媒にＨＣを供給するようにしたものがある。2. Description of the Related Art In recent years, it has been proposed to arrange a plurality of catalysts in series in an exhaust pipe of an internal combustion engine in order to improve exhaust gas purification performance of a vehicle. Further, in order to increase the NOx purification rate in exhaust gas of an oxygen-excess atmosphere such as a diesel engine, hydrocarbon (e.g., "H
It is effective to supply HC to the catalyst.

【０００３】ＮＯｘ浄化用の触媒は、図２に示すよう
に、所定のＮＯｘ浄化温度範囲（Ｔ１〜Ｔ３）でのみＮ
Ｏｘを浄化でき、触媒温度がＮＯｘ浄化ピーク温度（Ｔ
２）を越えると、触媒温度が上昇するに従って、ＮＯｘ
浄化率が低下し、一方、ＨＣ反応率（ＨＣ浄化率）がほ
ぼ１００％になるという特性がある。従って、直列に配
置した触媒の最上流からＨＣを供給するシステムでは、
上流側触媒の温度がＮＯｘ浄化ピーク温度（Ｔ２）付近
又はそれ以上のときに、過剰のＨＣを供給すると上流側
触媒で多くのＨＣが反応して、そのＨＣの反応熱で上流
側触媒の温度が更に上昇し、ＮＯｘ浄化率が低下すると
いう悪循環に陥る。As shown in FIG. 2, the catalyst for purifying NOx is N only in a predetermined NOx purification temperature range (T1 to T3).
Ox can be purified, and the catalyst temperature becomes NOx purification peak temperature (T
After 2), as the catalyst temperature rises, NOx
There is a characteristic that the purification rate decreases, while the HC reaction rate (HC purification rate) becomes almost 100%. Therefore, in a system for supplying HC from the uppermost stream of the catalyst arranged in series,
When the temperature of the upstream catalyst is near or higher than the NOx purification peak temperature (T2), if excessive HC is supplied, a large amount of HC reacts in the upstream catalyst, and the heat of reaction of the HC causes the temperature of the upstream catalyst to increase. Further rises, and the NOx purification rate falls, resulting in a vicious cycle.

【０００４】このようになると、上流側触媒がＮＯｘ浄
化温度範囲を越えて過昇温状態となり、上流側触媒でＮ
Ｏｘを浄化できなくなるばかりか、供給したＨＣのほぼ
全量が上流側触媒で反応して下流側触媒にＨＣを供給で
きなくなったり、過昇温状態の上流側触媒から排出され
る高温の排気ガスにより下流側触媒も過昇温状態とな
り、下流側触媒でもＮＯｘを浄化できなくなる。しか
も、触媒に供給するＨＣは、燃料が使用されるため、過
昇温状態の触媒ではＨＣが無駄に消費されることにな
り、燃費が悪化することにもなる。In this case, the temperature of the upstream side catalyst exceeds the NOx purification temperature range, and the temperature of the upstream side catalyst becomes excessively high.
In addition to being unable to purify Ox, almost all of the supplied HC reacts with the upstream catalyst and cannot supply HC to the downstream catalyst, or the high temperature exhaust gas discharged from the overheated upstream catalyst causes The temperature of the downstream side catalyst also becomes excessively high, so that the downstream side catalyst cannot purify NOx. In addition, since fuel is used as the HC to be supplied to the catalyst, the HC in an excessively heated state is wasted and the fuel consumption is deteriorated.

【０００５】このような問題を解決するために、特開平
８−２８１０６９号公報に示すように、直列に配置した
複数個の触媒のそれぞれの上流にＨＣ供給装置を設け、
排気温度に応じて各触媒ヘのＨＣ供給量を個別に制御し
て、各触媒に適正量のＨＣを供給することが提案されて
いる。In order to solve such a problem, as shown in Japanese Patent Application Laid-Open No. Hei 8-28069, an HC supply device is provided upstream of each of a plurality of catalysts arranged in series.
It has been proposed to individually control the amount of HC supplied to each catalyst according to the exhaust gas temperature and supply an appropriate amount of HC to each catalyst.

【０００６】[0006]

【発明が解決しようとする課題】しかし、上記公報の構
成では、複数の触媒のそれぞれにＨＣ供給装置が１つず
つ必要になることから構成が複雑になり、コストが高く
なるばかりか、装置が大型化するという問題がある。However, the configuration disclosed in the above publication requires a single HC supply device for each of a plurality of catalysts, which complicates the configuration, increases the cost, and increases the cost of the device. There is a problem that the size is increased.

【０００７】本発明はこのような事情を考慮してなされ
たものであり、従ってその目的は、簡単でコンパクトな
構成で、直列に配置した複数の触媒に適正量のＨＣを供
給でき、ＮＯｘ浄化率と燃費を向上させることができる
内燃機関の排気浄化装置を提供することにある。SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and has as its object to provide a simple and compact structure capable of supplying an appropriate amount of HC to a plurality of catalysts arranged in series, and It is an object of the present invention to provide an exhaust gas purification device for an internal combustion engine that can improve the efficiency and fuel efficiency.

【０００８】[0008]

【課題を解決するための手段】上記目的を達成するため
に、本発明の請求項１の内燃機関の排気浄化装置は、上
流側触媒の温度を上流側触媒温度判定手段で判定し、下
流側触媒の温度を下流側触媒温度判定手段で判定する。
そして、基本供給量決定手段により、少なくとも上流側
触媒の判定温度と運転状態とに基づいて基本炭化水素供
給量（以下「基本ＨＣ供給量」と表記する）を算出する
と共に、補正供給量決定手段により、少なくとも下流側
触媒の判定温度と運転状態とに基づいて補正炭化水素供
給量（以下「補正ＨＣ供給量」と表記する）を算出し、
炭化水素供給量決定手段により、基本ＨＣ供給量を補正
ＨＣ供給量で補正してＨＣ供給量を決定する。To achieve the above object, an exhaust gas purifying apparatus for an internal combustion engine according to claim 1 of the present invention determines the temperature of an upstream catalyst by an upstream catalyst temperature determining means, The temperature of the catalyst is determined by the downstream catalyst temperature determination means.
The basic supply amount determining means calculates a basic hydrocarbon supply amount (hereinafter, referred to as “basic HC supply amount”) based on at least the determination temperature and the operating state of the upstream catalyst, and corrects the supply amount. Calculates a corrected hydrocarbon supply amount (hereinafter referred to as a “corrected HC supply amount”) based on at least the determination temperature and the operating state of the downstream catalyst,
The hydrocarbon supply amount determining means corrects the basic HC supply amount with the corrected HC supply amount to determine the HC supply amount.

【０００９】この場合、上流側触媒の判定温度は上流側
触媒の活性状態を代表するパラメータであり、下流側触
媒の判定温度は下流側触媒の活性状態を代表するパラメ
ータであるため、上流側触媒の判定温度を考慮して求め
られる基本ＨＣ供給量は上流側触媒の活性状態を反映し
た値となり、下流側触媒の判定温度を考慮して求められ
る補正ＨＣ供給量は下流側触媒の活性状態を反映した値
となる。従って、基本ＨＣ供給量を補正ＨＣ供給量で補
正して求められるＨＣ供給量は、上流側触媒と下流側触
媒の双方の活性状態を考慮した適切な値となる。これに
より、各触媒へのＨＣの過剰供給を回避できて、上流側
触媒と下流側触媒が過昇温状態になることを防止でき、
複数の触媒を全て有効に使用して、必要最少量のＨＣ供
給量で排気中のＮＯｘを効率良く浄化することができ、
ＮＯｘ浄化率と燃費を向上させることができる。しか
も、前記公知例のように触媒の個数と同数のＨＣ供給装
置を設ける必要がなく、装置の構成を簡単化することが
できて、装置を小型化・低コスト化することができる。In this case, the determination temperature of the upstream catalyst is a parameter representing the activation state of the upstream catalyst, and the determination temperature of the downstream catalyst is a parameter representing the activation state of the downstream catalyst. The basic HC supply amount determined in consideration of the determination temperature of the above becomes a value reflecting the activation state of the upstream catalyst, and the corrected HC supply amount determined in consideration of the determination temperature of the downstream catalyst depends on the activation state of the downstream catalyst. The value is reflected. Therefore, the HC supply amount obtained by correcting the basic HC supply amount with the corrected HC supply amount is an appropriate value in consideration of the activation states of both the upstream catalyst and the downstream catalyst. As a result, excessive supply of HC to each catalyst can be avoided, and it is possible to prevent the upstream catalyst and the downstream catalyst from being in an excessively high temperature state,
By effectively using all of the plurality of catalysts, it is possible to efficiently purify NOx in exhaust gas with a minimum necessary HC supply amount,
The NOx purification rate and fuel economy can be improved. Moreover, it is not necessary to provide the same number of HC supply devices as the number of catalysts as in the above-described known example, so that the configuration of the device can be simplified, and the size and cost of the device can be reduced.

【００１０】この場合、請求項２のように、基本ＨＣ供
給量の最大値Ｑ１max を補正ＨＣ供給量の最大値Ｑ２ma
x よりも大きく設定することが好ましい。例えば、上流
側触媒の温度がＮＯｘ浄化上限温度（図２のＴ３）付近
で、下流側触媒の温度がＮＯｘ浄化ピーク温度（図２の
Ｔ２）付近の場合には、上流側触媒の活性状態が反映さ
れる基本ＨＣ供給量は少量であり、下流側触媒の活性状
態が反映される補正ＨＣ供給量は、最大値Ｑ２max に近
い値となるため、ＨＣ供給量は、補正ＨＣ供給量の最大
値Ｑ２max が寄与する度合いが大きくなる。この場合に
は、Ｑ１max ＞Ｑ２max とした方が、Ｑ１max ＜Ｑ２ma
x とするよりもＨＣ供給量が少なくなるため、高温の上
流側触媒に過剰のＨＣを供給することを防止できて、上
流側触媒の過昇温を抑えることができ、下流側触媒の過
昇温も抑えることができる。In this case, the maximum value Q1max of the basic HC supply amount is changed to the maximum value Q2ma of the corrected HC supply amount.
It is preferable to set larger than x. For example, when the temperature of the upstream catalyst is near the NOx purification upper limit temperature (T3 in FIG. 2) and the temperature of the downstream catalyst is near the NOx purification peak temperature (T2 in FIG. 2), the activation state of the upstream catalyst becomes Since the reflected basic HC supply amount is small and the corrected HC supply amount reflecting the activation state of the downstream side catalyst is a value close to the maximum value Q2max, the HC supply amount is the maximum value of the corrected HC supply amount. The degree to which Q2max contributes increases. In this case, Q1max> Q2max is better when Q1max <Q2ma.
Since the amount of HC supply is smaller than x, it is possible to prevent the supply of excess HC to the high-temperature upstream catalyst, to suppress the overheating of the upstream catalyst, and to prevent the overheating of the downstream catalyst. The temperature can be reduced.

【００１１】また、例えば、上流側触媒と下流側触媒の
温度が共にＮＯｘ浄化ピーク温度（図２のＴ２）付近の
場合、基本ＨＣ供給量と補正ＨＣ供給量が共に最大値Ｑ
１max ，Ｑ２max に近い値となるため、ＨＣ供給量は最
大値に近い値となる。この場合、多量のＨＣが上流側触
媒に供給され、上流側触媒で反応するＨＣが増加するた
め、その反応熱により上流側触媒がＮＯｘ浄化上限温度
（図２のＴ３）付近まで上昇し、更に、この上流側触媒
の流出ガス温度（下流側触媒の流入ガス温度）の上昇に
より下流側触媒もＮＯｘ浄化温度の上限付近まで上昇
し、上流側触媒と下流側触媒の双方のＮＯｘ浄化率が低
下する。For example, when the temperatures of the upstream catalyst and the downstream catalyst are both near the NOx purification peak temperature (T2 in FIG. 2), both the basic HC supply amount and the corrected HC supply amount become the maximum value Q.
Since the values are close to 1max and Q2max, the HC supply amount is close to the maximum value. In this case, a large amount of HC is supplied to the upstream catalyst, and the amount of HC that reacts on the upstream catalyst increases. Therefore, the heat of the reaction causes the upstream catalyst to rise to near the upper limit temperature of NOx purification (T3 in FIG. 2). Due to the rise of the outflow gas temperature of the upstream catalyst (the inflow gas temperature of the downstream catalyst), the downstream catalyst also rises to near the upper limit of the NOx purification temperature, and the NOx purification rates of both the upstream catalyst and the downstream catalyst decrease. I do.

【００１２】そこで、請求項３のように、ＨＣ供給量の
上限値（以下「上限ＨＣ供給量」という）Ｑmax を基本
ＨＣ供給量の最大値Ｑ１max と同一又はそれ以下に設定
すると良い。このようにすれば、上流側触媒と下流側触
媒の温度が共にＮＯｘ浄化ピーク温度付近の場合でも、
ＨＣ供給量が基本ＨＣ供給量の最大値Ｑ１max と同一又
はそれ以下となるため、上流側触媒の浄化能力を例えば
７〜８割程度に抑えることができ、上流側触媒の過昇温
を抑制できると共に、上流側触媒の流出ガス温度（下流
側触媒の流入ガス温度）の上昇を抑制して、下流側触媒
の過昇温を抑制でき、上流側触媒と下流側触媒の双方の
温度をＮＯｘ浄化温度範囲内に保つことができる。Therefore, the upper limit value (hereinafter referred to as the "upper limit HC supply amount") Qmax of the HC supply amount is preferably set to be equal to or less than the maximum value Q1max of the basic HC supply amount. With this configuration, even when the temperatures of the upstream catalyst and the downstream catalyst are both near the NOx purification peak temperature,
Since the HC supply amount is equal to or less than the maximum value Q1max of the basic HC supply amount, the purification capacity of the upstream side catalyst can be suppressed to, for example, about 70 to 80%, and the excessive temperature rise of the upstream side catalyst can be suppressed. At the same time, it is possible to suppress a rise in the outflow gas temperature of the upstream catalyst (the inflow gas temperature of the downstream catalyst), thereby suppressing an excessive rise in the temperature of the downstream catalyst, and purify the temperatures of both the upstream catalyst and the downstream catalyst in NOx It can be kept within the temperature range.

【００１３】この場合、請求項４のように、上限ＨＣ供
給量Ｑmax を上流側触媒の判定温度に応じて変化させる
ようにしても良く、例えば、上流側触媒の温度がＮＯｘ
浄化ピーク温度のときに上限ＨＣ供給量Ｑmax が最大と
なり、ＮＯｘ浄化温度範囲の下限・上限で上限ＨＣ供給
量Ｑmax が最小となるように設定しても良い。このよう
にすれば、上流側触媒の温度がＮＯｘ浄化下限温度付近
の時に、上限ＨＣ供給量Ｑmax によりＨＣ供給量を少な
くして上流側触媒ヘのＨＣ吸着量を少なくすることがで
き、上流側触媒のＨＣ被毒（ＨＣが触媒表面を覆ってし
まう状態）を抑えることができて、ＨＣ被毒によるＮＯ
ｘ浄化能力低下を防止できる。また、上流側触媒の温度
がＮＯｘ浄化上限温度付近の場合にも、上限ＨＣ供給量
Ｑmax によりＨＣ供給量を少なくすることができるた
め、上流側触媒でのＨＣ反応量を少なくすることがで
き、上流側触媒が過昇温状態になることを防止できる。In this case, the upper limit HC supply amount Qmax may be changed according to the determination temperature of the upstream catalyst, for example, when the temperature of the upstream catalyst is NOx.
The upper limit HC supply amount Qmax may be set such that the upper limit HC supply amount Qmax becomes maximum at the purification peak temperature and the upper limit HC supply amount Qmax becomes minimum at the lower and upper limits of the NOx purification temperature range. With this configuration, when the temperature of the upstream side catalyst is near the NOx purification lower limit temperature, the HC supply amount can be reduced by the upper limit HC supply amount Qmax, so that the amount of HC adsorbed to the upstream side catalyst can be reduced. HC poisoning of the catalyst (a state in which HC covers the catalyst surface) can be suppressed, and NO due to HC poisoning can be reduced.
x A reduction in purification ability can be prevented. Further, even when the temperature of the upstream side catalyst is near the NOx purification upper limit temperature, the HC supply amount can be reduced by the upper limit HC supply amount Qmax, so that the amount of HC reaction in the upstream side catalyst can be reduced, It is possible to prevent the upstream side catalyst from being in an excessively high temperature state.

【００１４】更に、請求項５のように、基本ＨＣ供給量
又は補正ＨＣ供給量の触媒温度に対する増減特性を、Ｎ
Ｏｘ浄化ピーク温度以上の領域での触媒温度上昇による
減少割合が、ＮＯｘ浄化ピーク温度以下の領域での触媒
温度上昇による増加割合よりも大きくなるように設定し
ても良い。Further, the characteristic of increasing / decreasing the basic HC supply amount or the corrected HC supply amount with respect to the catalyst temperature is expressed by N
The rate of decrease due to the increase in the catalyst temperature in the region equal to or higher than the Ox purification peak temperature may be set to be larger than the increase rate due to the increase in the catalyst temperature in the region equal to or lower than the NOx purification peak temperature.

【００１５】例えば、基本ＨＣ供給量の増減特性を、Ｎ
Ｏｘ浄化ピーク温度以上の領域での減少割合がＮＯｘ浄
化ピーク温度以下の領域での増加割合よりも大きくなる
ように設定すれば、上流側触媒がＮＯｘ浄化ピーク温度
以上の領域では、触媒温度が高くなるほど、基本ＨＣ供
給量が急激に低減されるため、上流側触媒へのＨＣ供給
量が急激に低減されて、上流側触媒でのＨＣの反応熱が
急激に低減される。これにより、上流側触媒が過昇温状
態となることを防止でき、上流側触媒の流出ガス温度の
上昇を抑えることができ、下流側触媒が過昇温状態とな
ることも防止できる。For example, the change characteristic of the basic HC supply amount is expressed as N
If the reduction rate in the region above the Ox purification peak temperature is set to be larger than the increase ratio in the region below the NOx purification peak temperature, the catalyst temperature becomes high in the region where the upstream catalyst is above the NOx purification peak temperature. Indeed, since the basic HC supply amount is rapidly reduced, the HC supply amount to the upstream side catalyst is rapidly reduced, and the reaction heat of HC in the upstream side catalyst is rapidly reduced. Accordingly, the upstream catalyst can be prevented from being in an excessively high temperature state, the rise in the outflow gas temperature of the upstream catalyst can be suppressed, and the downstream catalyst can also be prevented from being in an excessively high temperature state.

【００１６】また、補正ＨＣ供給量の増減特性を、ＮＯ
ｘ浄化ピーク温度以上の領域での減少割合がＮＯｘ浄化
ピーク温度以下の領域での増加割合よりも大きくなるよ
うに設定すれば、下流側触媒がＮＯｘ浄化ピーク温度以
上の領域では、触媒温度が高くなるほど、補正ＨＣ供給
量が急激に低減されるため、下流側触媒へのＨＣ供給量
が急激に低減されて、下流側触媒でのＨＣの反応熱が急
激に低減される。これにより、下流側触媒が過昇温状態
となることを防止できる。The change characteristic of the corrected HC supply amount is represented by NO
If the decrease rate in the region above the x purification peak temperature is set to be larger than the increase ratio in the region below the NOx purification peak temperature, the catalyst temperature becomes high in the region where the downstream catalyst is above the NOx purification peak temperature. In other words, the corrected HC supply amount is rapidly reduced, so that the HC supply amount to the downstream catalyst is rapidly reduced, and the reaction heat of HC in the downstream catalyst is rapidly reduced. Thereby, it is possible to prevent the downstream catalyst from being in an excessively high temperature state.

【００１７】一方、請求項６のように、上流側触媒と下
流側触媒のＮＯｘ浄化率に応じて複数の温度ゾーンに区
分し、上流側触媒の判定温度が属する温度ゾーンと下流
側触媒の判定温度が属する温度ゾーンとの組み合わせに
より基本ＨＣ供給量を補正してＨＣ供給量を決定するよ
うにしても良い。このようにしても、前記請求項１と同
じく、上流側触媒と下流側触媒の双方の活性状態を考慮
した適切なＨＣ供給量を設定することができ、ＮＯｘ浄
化率と燃費を向上させることができる。On the other hand, according to a sixth aspect, the temperature is divided into a plurality of temperature zones according to the NOx purification rates of the upstream catalyst and the downstream catalyst, and the temperature zone to which the determination temperature of the upstream catalyst belongs and the determination of the downstream catalyst are included. The HC supply amount may be determined by correcting the basic HC supply amount based on a combination with the temperature zone to which the temperature belongs. Also in this case, similarly to the first aspect, it is possible to set an appropriate HC supply amount in consideration of the activation states of both the upstream catalyst and the downstream catalyst, and to improve the NOx purification rate and fuel efficiency. it can.

【００１８】ここで、複数の温度ゾーンは、図２のＮＯ
ｘ浄化特性を考慮し、請求項７のように、ＮＯｘ浄化率
が低いレベルで推移する低温の第１の温度ゾーンと、Ｎ
Ｏｘ浄化率が温度と共に上昇する第２の温度ゾーンと、
ＮＯｘ浄化率が温度と共に低下する第３の温度ゾーン
と、ＮＯｘ浄化率が低いレベルで推移する高温の第４の
温度ゾーンとに区分すると良い。このようにすれば、Ｎ
Ｏｘ浄化特性に適合した温度ゾーンの区分とすることが
できる。Here, the plurality of temperature zones correspond to NO in FIG.
In consideration of the x purification characteristics, a first temperature zone at a low temperature where the NOx purification rate changes at a low level,
A second temperature zone in which the Ox purification rate increases with temperature;
It is preferable to divide into a third temperature zone in which the NOx purification rate decreases with temperature and a high-temperature fourth temperature zone in which the NOx purification rate changes at a low level. In this way, N
It can be divided into temperature zones suitable for Ox purification characteristics.

【００１９】この場合、請求項８のように、上流側触媒
の判定温度が第２の温度ゾーン（ＮＯｘ浄化温度範囲内
の低温側）又は第３の温度ゾーン（ＮＯｘ浄化温度範囲
内の高温側）に属し且つ下流側触媒の判定温度が第１乃
至第３の温度ゾーンのいずれかに属しているときに、基
本ＨＣ供給量を増量補正するようにしても良い。この増
量補正により、ＮＯｘ浄化温度範囲内にある上流側触媒
のＮＯｘ浄化量（ＨＣ反応量）を増加しつつ、上流側触
媒を通り抜けて下流側触媒に到達するＨＣを増加させ
る。このとき、下流側触媒の温度が第１の温度ゾーン
（ＮＯｘ浄化温度範囲より低温）に属する場合には、下
流側触媒に到達したＨＣは、下流側触媒に吸着される。
そして、吸着されたＨＣは、下流側触媒が第２の温度ゾ
ーンに昇温したときに離脱し、上流側触媒で浄化しきれ
なかったＮＯｘと反応してＮＯｘを浄化する。また、下
流側触媒の判定温度が第２又は第３の温度ゾーン（ＮＯ
ｘ浄化温度範囲内）に属する場合には、下流側触媒に到
達したＨＣは、上流側触媒で浄化しきれなかったＮＯｘ
と反応してＮＯｘを浄化する。In this case, the determination temperature of the upstream side catalyst is determined in the second temperature zone (low temperature side in the NOx purification temperature range) or the third temperature zone (high temperature range in the NOx purification temperature range). ), And when the determination temperature of the downstream catalyst belongs to any of the first to third temperature zones, the basic HC supply amount may be increased. By this increase correction, the amount of HC passing through the upstream catalyst and reaching the downstream catalyst is increased while increasing the NOx purification amount (HC reaction amount) of the upstream catalyst within the NOx purification temperature range. At this time, when the temperature of the downstream catalyst belongs to the first temperature zone (lower than the NOx purification temperature range), the HC that has reached the downstream catalyst is adsorbed by the downstream catalyst.
Then, the adsorbed HC is released when the downstream catalyst rises to the second temperature zone, and reacts with NOx that cannot be completely purified by the upstream catalyst to purify NOx. Further, the determination temperature of the downstream side catalyst is set in the second or third temperature zone (NO
x within the purification temperature range), the HC that has reached the downstream catalyst is NOx that cannot be completely purified by the upstream catalyst.
To purify NOx.

【００２０】ここで、下流側触媒の温度が第１の温度ゾ
ーンに属する場合、供給するＨＣが多過ぎると、下流側
触媒にＨＣ被毒が発生し、下流側触媒のＮＯｘ浄化能力
が低下する。また、燃費悪化が増大してしまう。Here, when the temperature of the downstream catalyst belongs to the first temperature zone, if too much HC is supplied, HC poisoning occurs in the downstream catalyst, and the NOx purification ability of the downstream catalyst is reduced. . In addition, the deterioration of fuel efficiency increases.

【００２１】この対策として、請求項９のように、下流
側触媒の判定温度が第１の温度ゾーン（ＮＯｘ浄化温度
範囲より低温）に属しているときに、基本ＨＣ供給量を
所定期間のみ増量補正することが好ましい。これによ
り、下流側触媒のＨＣ被毒を防止できると共に、燃費悪
化を抑制でき、更に、下流側触媒が第２の温度ゾーンに
昇温したときのＮＯｘ浄化性能を確保することができ
る。As a countermeasure, when the determination temperature of the downstream side catalyst belongs to the first temperature zone (lower than the NOx purification temperature range), the basic HC supply amount is increased only for a predetermined period. It is preferable to correct. Thereby, HC poisoning of the downstream side catalyst can be prevented, deterioration of fuel efficiency can be suppressed, and NOx purification performance when the temperature of the downstream side catalyst rises to the second temperature zone can be ensured.

【００２２】また、上流側触媒の判定温度が第３の温度
ゾーンに属している場合には、上流側触媒の流出ガス温
度が比較的高温である。従って、下流側触媒の判定温度
が第３の温度ゾーンに属する場合に、ＨＣ供給量が多く
なり過ぎると、下流側触媒が過昇温状態となりやすい。When the determination temperature of the upstream catalyst belongs to the third temperature zone, the outflow gas temperature of the upstream catalyst is relatively high. Therefore, when the determination temperature of the downstream catalyst belongs to the third temperature zone, if the HC supply amount becomes too large, the downstream catalyst is likely to be in an excessively high temperature state.

【００２３】この対策として、請求項１０のように、下
流側触媒の判定温度が第３の温度ゾーン（ＮＯｘ浄化温
度範囲内の高温側）に属している場合の基本ＨＣ供給量
に対する増量補正量を下流側触媒の判定温度が第２の温
度ゾーンに属している場合よりも小さく設定することが
好ましい。このようにすれば、下流側触媒の判定温度が
第３の温度ゾーンに属しているときに、下流側触媒での
ＨＣ反応量（発熱量）を下流側触媒の判定温度が第２の
温度ゾーンに属している場合よりも少なくして、下流側
触媒の過昇温を抑えることができ、下流側触媒の温度を
ＮＯｘ浄化温度範囲内に維持することができる。As a countermeasure, an increase correction amount with respect to the basic HC supply amount when the determination temperature of the downstream side catalyst belongs to the third temperature zone (high temperature side within the NOx purification temperature range). Is preferably set lower than when the determination temperature of the downstream catalyst belongs to the second temperature zone. With this configuration, when the determination temperature of the downstream catalyst belongs to the third temperature zone, the HC reaction amount (heat generation amount) of the downstream catalyst is reduced by the determination temperature of the downstream catalyst to the second temperature zone. , The excessive temperature rise of the downstream catalyst can be suppressed, and the temperature of the downstream catalyst can be maintained within the NOx purification temperature range.

【００２４】更に、請求項１１のように、上流側触媒の
判定温度が第１の温度ゾーン（ＮＯｘ浄化温度範囲より
低温）に属し且つ下流側触媒の判定温度が第２の温度ゾ
ーン又は第３の温度ゾーンに属しているときに、基本Ｈ
Ｃ供給量を増量補正するようにしても良い。つまり、上
流側触媒の判定温度が第１の温度ゾーンに属している場
合には、基本ＨＣ供給量は少量又は０となるが、これを
増量補正することにより、供給されるＨＣの一部は上流
側触媒に吸着され、残りのＨＣは上流側触媒を通り抜
け、下流側触媒でＮＯｘと反応してＮＯｘを浄化する。
また、上流側触媒に吸着したＨＣは、上流側触媒が第２
の温度ゾーンに昇温したときに離脱し、上流側触媒又は
下流側触媒でＮＯｘと反応してＮＯｘを浄化する。Further, the determination temperature of the upstream catalyst belongs to the first temperature zone (lower than the NOx purification temperature range) and the determination temperature of the downstream catalyst falls in the second temperature zone or the third temperature zone. The basic H
The C supply amount may be increased. That is, when the determination temperature of the upstream side catalyst belongs to the first temperature zone, the basic HC supply amount becomes small or 0, but by increasing this, a part of the supplied HC is reduced. The remaining HC is adsorbed by the upstream catalyst, passes through the upstream catalyst, and reacts with NOx on the downstream catalyst to purify NOx.
Further, the HC adsorbed on the upstream side catalyst is separated by the upstream side catalyst into the second
When the temperature rises to the temperature zone of NO, the catalyst is released and reacts with NOx at the upstream catalyst or the downstream catalyst to purify NOx.

【００２５】この場合、請求項１２のように、基本ＨＣ
供給量に対する増量補正量を時間の経過と共に減少させ
ることが好ましい。これにより、上流側触媒のＨＣ被毒
を防止でき、上流側触媒が第２の温度ゾーンに昇温した
ときに、効果的にＮＯｘを浄化できる。In this case, the basic HC may be used.
It is preferable to decrease the increase correction amount with respect to the supply amount with the passage of time. Thereby, HC poisoning of the upstream side catalyst can be prevented, and when the temperature of the upstream side catalyst rises to the second temperature zone, NOx can be effectively purified.

【００２６】また、請求項１３のように、窒素酸化物排
出量算出手段により内燃機関の運転状態からＮＯｘ排出
量を算出し、上流側触媒の判定温度、下流側触媒の判定
温度及びＮＯｘ排出量に基づいて三次元マップ等から直
接、ＨＣ供給量を決定するようにしても良い。このよう
にすれば、簡単な処理でＨＣ供給量を決定することがで
きる。Further, the NOx emission amount is calculated from the operating state of the internal combustion engine by the nitrogen oxide emission amount calculating means, and the determination temperature of the upstream catalyst, the determination temperature of the downstream catalyst, and the NOx emission amount are calculated. May be determined directly from a three-dimensional map or the like based on the above. In this way, the HC supply amount can be determined by a simple process.

【００２７】[0027]

【発明の実施の形態】［実施形態（１）］以下、本発明
をディーゼルエンジンに適用した実施形態（１）を図１
乃至図１６に基づいて説明する。まず、図１に基づいて
エンジン制御システム全体の構成を説明する。内燃機関
であるディーゼルエンジン１０の各気筒には、吸気管１
１を通して吸入される吸入空気が吸気マニホールド１２
を通して吸入される。ディーゼルエンジン１０の各気筒
には、電磁弁式の燃料噴射弁１４が取り付けられ、各燃
料噴射弁１４には、高圧燃料ポンプ１５から高圧に畜圧
された燃料が燃料配管１６を通して分配される。DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [Embodiment (1)] FIG. 1 shows an embodiment (1) in which the present invention is applied to a diesel engine.
This will be described with reference to FIGS. First, the configuration of the entire engine control system will be described with reference to FIG. Each cylinder of a diesel engine 10, which is an internal combustion engine, has an intake pipe 1
1 is drawn through the intake manifold 12
Inhaled through. An electromagnetic valve type fuel injection valve 14 is attached to each cylinder of the diesel engine 10, and fuel pressurized to a high pressure from a high pressure fuel pump 15 is distributed to each fuel injection valve 14 through a fuel pipe 16.

【００２８】燃料噴射弁１４は、圧縮上死点近傍でエン
ジン出力発生のための主燃料噴射を行うと共に、少なく
とも１つの気筒の燃料噴射弁１４は、膨脹行程又は排気
行程において後述する上流側触媒１９と下流側２０にＮ
Ｏｘの還元剤としてＨＣを供給するための後噴射を実行
する炭化水素供給手段として機能する。The fuel injection valve 14 performs main fuel injection for generating engine output in the vicinity of the compression top dead center, and the fuel injection valve 14 of at least one cylinder has an upstream catalyst, which will be described later in an expansion stroke or an exhaust stroke. N at 19 and downstream 20
It functions as a hydrocarbon supply means for executing post-injection for supplying HC as a reducing agent for Ox.

【００２９】ディーゼルエンジン１０の各気筒から排出
される排気ガスは、排気マニホールド１７を通して１本
の排気管１８（排気通路）に排出され、この排気管１８
の途中に、上流側触媒１９と下流側触媒２０が直列に配
設されている。各触媒１９，２０は、セラミックや金属
等の担体の表面に、酸素過剰雰囲気中でも還元剤（Ｈ
Ｃ）の存在下でＮＯｘを還元浄化可能な触媒成分（例え
ばＰｔ−ゼオライト）を担持したＮＯｘ触媒である。Exhaust gas discharged from each cylinder of the diesel engine 10 is discharged through an exhaust manifold 17 to a single exhaust pipe 18 (exhaust passage).
, An upstream catalyst 19 and a downstream catalyst 20 are arranged in series. Each of the catalysts 19, 20 is provided with a reducing agent (H
The NOx catalyst supports a catalyst component (for example, Pt-zeolite) capable of reducing and purifying NOx in the presence of C).

【００３０】これら上流側及び下流側触媒１９，２０の
浄化特性は、図２に示すように触媒温度がＴ１未満の温
度領域では、ＮＯｘもＨＣもほとんど浄化されず、触媒
温度がＴ１以上になると、ＮＯｘとＨＣの浄化が開始さ
れる。ＮＯｘ浄化率は、Ｔ２でほぼ最高値を示し、Ｔ３
以上の温度領域では、ＮＯｘ浄化率が略０となる過昇温
状態となる。このように、ＮＯｘは、触媒温度がＴ１〜
Ｔ３の温度範囲（ＮＯｘ浄化温度範囲）にある場合のみ
浄化される。As shown in FIG. 2, the purification characteristics of the upstream and downstream catalysts 19 and 20 are such that when the catalyst temperature is lower than T1, NOx and HC are hardly purified, and when the catalyst temperature becomes higher than T1. , NOx and HC purification are started. The NOx purification rate shows almost the highest value at T2, and T3
In the above temperature range, an excessively high temperature state in which the NOx purification rate becomes substantially zero is obtained. As described above, NOx has a catalyst temperature of T1 to T1.
Purification is performed only in the temperature range of T3 (NOx purification temperature range).

【００３１】上流側及び下流側触媒１９，２０の触媒成
分が例えばＰｔ−ゼオライトの場合には、Ｔ１は約２０
０℃、Ｔ２は約２５０℃、Ｔ３は約３００℃である。ま
た、上流側及び下流側触媒１９，２０の触媒成分をＣｕ
−ゼオライトとした場合は、Ｔ１は約３００℃、Ｔ２は
約４００℃、Ｔ３は約５００℃となる。When the catalyst components of the upstream and downstream catalysts 19 and 20 are, for example, Pt-zeolite, T1 is about 20
0 ° C., T2 is about 250 ° C., and T3 is about 300 ° C. The catalyst components of the upstream and downstream catalysts 19, 20 are Cu
-In the case of zeolite, T1 is about 300C, T2 is about 400C, and T3 is about 500C.

【００３２】上流側及び下流側触媒１９，２０の出口部
には、それぞれ排気温度センサ２１，２２が設置されて
いる。排気温度センサ２１は、上流側触媒１９の流出ガ
ス温度を検出することで、上流側触媒１９の触媒温度を
判定する上流側触媒温度判定手段としての役割を果た
し、排気温度センサ２２は、下流側触媒２０の流出ガス
温度を検出することで、下流側触媒２０の触媒温度を判
定する下流側触媒温度判定手段としての役割を果たす。Exhaust temperature sensors 21 and 22 are installed at the outlets of the upstream and downstream catalysts 19 and 20, respectively. The exhaust gas temperature sensor 21 functions as an upstream catalyst temperature determining unit that determines the catalyst temperature of the upstream catalyst 19 by detecting the outflow gas temperature of the upstream catalyst 19, and the exhaust gas temperature sensor 22 By detecting the outflow gas temperature of the catalyst 20, it functions as a downstream catalyst temperature determining means for determining the catalyst temperature of the downstream catalyst 20.

【００３３】これらの排気温度センサ２１，２２の出力
信号は、エンジン電子制御回路（以下「ＥＣＵ」とい
う）２３に入力される。このＥＣＵ２３に内蔵されたＲ
ＯＭ（記憶媒体）には、図３に示す噴射制御プログラム
が記憶されている。The output signals of these exhaust temperature sensors 21 and 22 are input to an engine electronic control circuit (hereinafter referred to as "ECU") 23. R built into this ECU 23
The injection control program shown in FIG. 3 is stored in the OM (storage medium).

【００３４】以下、ＥＣＵ２３によって実行される噴射
制御プログラムの内容を図３のフローチャートに従って
説明する。この噴射制御プログラムは、各気筒の噴射タ
イミング毎に実行される。本プログラムが起動される
と、まずステップ１０１で、ディーゼルエンジン１０の
運転状態を検出するために、アクセルセンサ２５、エン
ジン回転数センサ２４の出力信号を読み込むと共に、上
流側及び下流側触媒１９，２０の温度を判定するため
に、排気温度センサ２１，２２の出力信号を読み込む。
この後、ステップ１０２で、アクセルセンサ２５とエン
ジン回転数センサ２４の出力信号に基づいてエンジン出
力を得るための主燃料噴射量を算出する。Hereinafter, the contents of the injection control program executed by the ECU 23 will be described with reference to the flowchart of FIG. This injection control program is executed at each injection timing of each cylinder. When the program is started, first, in step 101, in order to detect the operating state of the diesel engine 10, the output signals of the accelerator sensor 25 and the engine speed sensor 24 are read, and the upstream and downstream catalysts 19 and 20 are read. The output signals of the exhaust gas temperature sensors 21 and 22 are read to determine the temperature of the exhaust gas.
Thereafter, in step 102, the main fuel injection amount for obtaining the engine output is calculated based on the output signals of the accelerator sensor 25 and the engine speed sensor 24.

【００３５】この後、ステップ１０３で、アクセルセン
サ２５とエンジン回転数センサ２４の出力信号に基づい
てマップ（図示せず）等からディーゼルエンジン１０か
ら排出されるＮＯｘ量を推定し、次のステップ１０４
で、排気温度センサ２１，２２の出力信号から上流側触
媒１９と下流側触媒２０の温度を判定する。この場合、
排気温度センサ２１，２２は、それぞれ上流側触媒１
９，下流側触媒２０の出口部に設けられているため、排
気温度センサ２１で検出する温度は、上流側触媒１９の
流出ガス温度、ひいては上流側触媒１９の活性状態を表
す上流側触媒温度であり、排気温度センサ２２で検出す
る温度は、下流側触媒２０の流出ガス温度、ひいては下
流側触媒２０の活性状態を表す下流側触媒温度である。Thereafter, in step 103, the amount of NOx exhausted from the diesel engine 10 is estimated from a map (not shown) or the like based on the output signals of the accelerator sensor 25 and the engine speed sensor 24.
Then, the temperatures of the upstream catalyst 19 and the downstream catalyst 20 are determined from the output signals of the exhaust gas temperature sensors 21 and 22. in this case,
The exhaust gas temperature sensors 21 and 22 are connected to the upstream catalyst 1 respectively.
9. Since the exhaust gas temperature sensor 21 is provided at the outlet of the downstream catalyst 20, the temperature detected by the exhaust gas temperature sensor 21 is the temperature of the gas flowing out of the upstream catalyst 19, and thus the temperature of the upstream catalyst representing the activation state of the upstream catalyst 19. In addition, the temperature detected by the exhaust gas temperature sensor 22 is the temperature of the outflow gas of the downstream side catalyst 20 and the downstream side catalyst temperature indicating the activation state of the downstream side catalyst 20.

【００３６】次のステップ１０５で、図４（ａ）に示す
上流側触媒温度とＮＯｘ排出量とをパラメータとする基
本ＨＣ供給量Ｑ１のマップを検索し、現在の上流側触媒
温度とＮＯｘ排出量に応じた基本ＨＣ供給量Ｑ１を求め
る。この処理が特許請求の範囲でいう基本供給量決定手
段に相当する役割を果たす。更に、図４（ｂ）に示す下
流側触媒温度とＮＯｘ排出量とをパラメータとする補正
ＨＣ供給量Ｑ２のマップを検索し、現在の下流側触媒温
度とＮＯｘ排出量に応じた補正ＨＣ供給量Ｑ２を求め、
この補正ＨＣ供給量Ｑ２に、上流側触媒温度に応じて設
定される係数ｋ２を乗算して最終的な補正ＨＣ供給量ｋ
２・Ｑ２を求める。この処理が特許請求の範囲でいう補
正供給量決定手段に相当する役割を果たす。In the next step 105, a map of the basic HC supply amount Q1 is searched by using the upstream catalyst temperature and the NOx emission amount shown in FIG. 4A as parameters, and the current upstream catalyst temperature and the NOx emission amount are searched. The basic HC supply amount Q1 corresponding to the above is obtained. This processing plays a role corresponding to the basic supply amount determining means in the claims. Further, a map of the corrected HC supply amount Q2 using the downstream catalyst temperature and the NOx emission amount shown in FIG. 4B as parameters is searched, and the corrected HC supply amount according to the current downstream catalyst temperature and the NOx emission amount is searched. Find Q2,
This corrected HC supply amount Q2 is multiplied by a coefficient k2 set according to the upstream side catalyst temperature to obtain a final corrected HC supply amount k2.
2. Find Q2. This processing plays a role corresponding to the correction supply amount determining means in the claims.

【００３７】ＮＯｘ浄化に必要なＨＣ量は、各触媒１
９，２０の温度と、排気ガス中のＮＯｘ量とによって変
化する。これを考慮して、図４の基本ＨＣ供給量Ｑ１及
び補正ＨＣ供給量Ｑ２のマップは、触媒温度とＮＯｘ排
出量とをパラメータとする二次元マップとして設定され
ている。更に、基本ＨＣ供給量の最大値Ｑ１max は、補
正ＨＣ供給量の最大値Ｑ２max よりも大きく設定されて
いる。これらの基本ＨＣ供給量Ｑ１及び補正ＨＣ供給量
Ｑ２のマップは、予め、実験データや理論式によって設
定され、ＥＣＵ２３のＲＯＭに記憶されている。The amount of HC required for NOx purification is determined by
The temperature varies depending on the temperatures of NO. 9 and NO. 20 and the amount of NOx in the exhaust gas. In consideration of this, the map of the basic HC supply amount Q1 and the corrected HC supply amount Q2 in FIG. 4 is set as a two-dimensional map using the catalyst temperature and the NOx emission amount as parameters. Further, the maximum value Q1max of the basic HC supply amount is set to be larger than the maximum value Q2max of the corrected HC supply amount. The maps of the basic HC supply amount Q1 and the corrected HC supply amount Q2 are set in advance by experimental data and theoretical expressions, and are stored in the ROM of the ECU 23.

【００３８】また、補正ＨＣ供給量Ｑ２に乗算する係数
ｋ２は、例えば、上流側触媒温度が３００℃未満の場合
にはｋ２＝１、３００℃以上３３０℃未満の場合にはｋ
２＝０．５、３３０℃以上の場合にはｋ２＝０．１と設
定されている。このように、上流側触媒温度が高くなる
ほど係数ｋ２を小さくする理由は、上流側触媒１９の温
度が高いほど、供給されるＨＣが上流側触媒１９で酸素
と反応する量が増加して、ＨＣがＮＯｘの還元剤として
使われなくなるので、上流側触媒温度が高くなるほど、
補正ＨＣ供給量ｋ２・Ｑ２を減少させ、無駄に消費され
るＨＣ量（酸素と反応するＨＣ量）を少なくするためで
ある。The coefficient k2 by which the corrected HC supply amount Q2 is multiplied is, for example, k2 = 1 when the upstream catalyst temperature is lower than 300 ° C., and k2 when the upstream catalyst temperature is 300 ° C. or higher and lower than 330 ° C.
When 2 = 0.5 and 330 ° C. or higher, k2 = 0.1 is set. As described above, the reason that the coefficient k2 is reduced as the upstream catalyst temperature increases is that the higher the temperature of the upstream catalyst 19 is, the more the amount of supplied HC reacting with oxygen in the upstream catalyst 19 is increased. Is no longer used as a NOx reducing agent, so the higher the upstream catalyst temperature,
This is because the corrected HC supply amount k2 · Q2 is reduced to reduce the amount of HC that is wasted (the amount of HC that reacts with oxygen).

【００３９】そして、次のステップ１０６で、基本ＨＣ
供給量Ｑ１に補正ＨＣ供給量ｋ２・Ｑ２を加算して仮の
ＨＣ供給量Ｑ０を算出する（Ｑ０＝Ｑ１＋ｋ２・Ｑ
２）。直列に配置された上流側触媒１９と下流側触媒２
０は、１つの触媒と異なり、触媒温度（活性状態）が異
なることが多いため、上述した処理により上流側触媒１
９と下流側触媒２０の双方の活性状態（触媒温度）を考
慮したＨＣ供給量Ｑ０を算出する。Then, in the next step 106, the basic HC
The provisional HC supply amount Q0 is calculated by adding the corrected HC supply amount k2 · Q2 to the supply amount Q1 (Q0 = Q1 + k2 · Q).
2). Upstream catalyst 19 and downstream catalyst 2 arranged in series
0 is different from one catalyst, and the catalyst temperature (active state) is often different.
The HC supply amount Q0 is calculated in consideration of the activation states (catalyst temperatures) of both the fuel cell 9 and the downstream catalyst 20.

【００４０】尚、ＨＣ供給量は、例えば、上流側触媒温
度、下流側触媒温度及びＮＯｘ排出量をパラメータとす
るＨＣ供給量の三次元マップを作成しておき、このマッ
プから一度に、基本ＨＣ供給量と補正ＨＣ供給量を合計
したＨＣ供給量を求めるようにしても良い。For the HC supply amount, for example, a three-dimensional map of the HC supply amount is prepared by using the upstream catalyst temperature, the downstream catalyst temperature and the NOx emission amount as parameters, and the basic HC The HC supply amount obtained by adding the supply amount and the corrected HC supply amount may be obtained.

【００４１】ＨＣ供給量Ｑ０の算出後、ステップ１０７
に進み、上限ＨＣ供給量Ｑmax を読み込む。ここで、上
限ＨＣ供給量Ｑmax は、例えば基本ＨＣ供給量の最大値
Ｑ１max （一定）に設定されるが、基本ＨＣ供給量の最
大値Ｑ１max よりも小さい値に設定しても良い。After calculating the HC supply amount Q0, step 107
To read the upper limit HC supply amount Qmax. Here, the upper limit HC supply amount Qmax is set to, for example, the maximum value Q1max (constant) of the basic HC supply amount, but may be set to a value smaller than the maximum value Q1max of the basic HC supply amount.

【００４２】この後、ステップ１０８〜１１０で、ＨＣ
供給量Ｑ０を上限ＨＣ供給量Ｑmaxでガード処理する。
具体的には、ステップ１０８で、仮のＨＣ供給量Ｑ０が
上限ＨＣ供給量Ｑmax よりも小さいか否かを判定し、Ｑ
０＜Ｑ１max の場合は、ステップ１０９に進み、仮のＨ
Ｃ供給量Ｑ０をそのままＨＣ供給量Ｑとして採用し（Ｑ
＝Ｑ０）、Ｑ０≧Ｑ１max の場合は、ステップ１１０に
進み、上限ＨＣ供給量Ｑmax をＨＣ供給量Ｑとして採用
する（Ｑ＝Ｑmax ）。上記ステップ１０６〜１１０の処
理が特許請求の範囲でいう炭化水素供給量決定手段とし
ての役割を果たす。Thereafter, in steps 108 to 110, the HC
Guard processing is performed on the supply amount Q0 with the upper limit HC supply amount Qmax.
Specifically, at step 108, it is determined whether or not the provisional HC supply amount Q0 is smaller than the upper limit HC supply amount Qmax.
If 0 <Q1max, the routine proceeds to step 109, where temporary H
The C supply amount Q0 is directly used as the HC supply amount Q (Q
= Q0), if Q0 ≧ Q1max, the routine proceeds to step 110, where the upper limit HC supply amount Qmax is adopted as the HC supply amount Q (Q = Qmax). The processing of the above steps 106 to 110 plays a role as a hydrocarbon supply amount determining means referred to in the claims.

【００４３】この後、ステップ１１１で、各気筒の燃料
噴射弁１４に、ステップ１０２で算出した主燃料噴射量
で主燃料噴射を実施するように噴射指令を出力すると共
に、ステップ１０９又は１１０で決定したＨＣ供給量Ｑ
で後噴射を実施するように噴射指令を出力する。Thereafter, in step 111, an injection command is output to the fuel injection valve 14 of each cylinder so as to execute the main fuel injection with the main fuel injection amount calculated in step 102, and the determination is made in step 109 or 110. HC supply amount Q
Outputs an injection command so as to execute post-injection.

【００４４】以上説明した実施形態（１）の噴射制御プ
ログラムを実行した場合の具体例を図５乃至図１４を用
いて説明する。図５は、上流側触媒１９の温度ＴａがＮ
Ｏｘ浄化ピーク温度Ｔ２付近で分布し、下流側触媒２０
の温度ＴｂがＮＯｘ浄化ピーク温度Ｔ２よりも高温側で
分布している場合を示している。このような温度分布
は、ディーゼルエンジン１０が比較的高負荷の定常運転
状態から中負荷の運転状態に移行したときに発生する。A specific example when the injection control program of the embodiment (1) described above is executed will be described with reference to FIGS. FIG. 5 shows that the temperature Ta of the upstream side catalyst 19 is N
It is distributed around the Ox purification peak temperature T2, and the downstream side catalyst 20
3 shows a case where the temperature Tb is distributed on the higher temperature side than the NOx purification peak temperature T2. Such a temperature distribution occurs when the diesel engine 10 shifts from a relatively high load steady operation state to a medium load operation state.

【００４５】この場合、基本ＨＣ供給量Ｑ１は、図６
（ａ）に示すように、上流側触媒温度Ｔａに応じた比較
的多めの基本ＨＣ供給量Ｑ１ａに設定され、補正ＨＣ供
給量Ｑ２は、図６（ｂ）に示すように、下流側触媒温度
Ｔｂに応じた少量の補正ＨＣ供給量Ｑ２ｂに設定され
る。ここで、図６（ａ），（ｂ）は、それぞれ図４
（ａ），（ｂ）のマップから現在のＮＯｘ排出量に対応
する曲線を抽出したものである。また、係数ｋ２は、上
流側触媒温度Ｔａ（＜３００℃）に応じてｋ２＝１に設
定される。これにより、後噴射により供給されるＨＣ供
給量Ｑは、Ｑ＝Ｑａｂ＝Ｑ１ａ＋Ｑ２ｂ（但しＱａｂ＜
Ｑmax ）に設定される。In this case, the basic HC supply amount Q1 is as shown in FIG.
As shown in (a), a relatively large basic HC supply amount Q1a corresponding to the upstream catalyst temperature Ta is set, and the corrected HC supply amount Q2 is set as shown in FIG. A small correction HC supply amount Q2b corresponding to Tb is set. Here, FIGS. 6A and 6B correspond to FIGS.
The curves corresponding to the current NOx emissions are extracted from the maps of (a) and (b). The coefficient k2 is set to k2 = 1 according to the upstream catalyst temperature Ta (<300 ° C.). Thus, the HC supply amount Q supplied by the post-injection is Q = Qab = Q1a + Q2b (where Qab <
Qmax).

【００４６】この際、もし、ＨＣ供給量Ｑを上流側触媒
温度Ｔａのみから判定し、ＨＣ供給量Ｑ＝２×Ｑ１ａ
（>>Ｑａｂ）とすると、Ｑａｂより多いＨＣ量が上流側
触媒１９に供給され、その反応熱により上流側触媒１９
の温度がＮＯｘ浄化上限温度Ｔ３付近まで上昇してＮＯ
ｘ浄化率が低下してしまう。更に、上流側触媒１９を通
過して高温の下流側触媒２０に流入するＨＣ量は、Ｑ２
ｂよりもはるかに多い量であり、多量のＨＣが高温の下
流側触媒２０で反応するため、多量のＨＣの反応熱によ
り高温の下流側触媒２０の温度が更に上昇して過昇温状
態になってしまう。これにより、燃費の悪化とＮＯｘ浄
化能力の低下を招く。At this time, if the HC supply amount Q is determined only from the upstream catalyst temperature Ta, the HC supply amount Q = 2 × Q1a
(>> Qab), a larger amount of HC than Qab is supplied to the upstream catalyst 19, and the heat of the reaction causes the upstream catalyst 19 to react.
Temperature rises to near the NOx purification upper limit temperature T3 and the NO
x The purification rate decreases. Further, the amount of HC flowing into the high-temperature downstream catalyst 20 through the upstream catalyst 19 is Q2
b), a large amount of HC reacts in the high-temperature downstream catalyst 20, and the temperature of the high-temperature downstream catalyst 20 further rises due to the heat of reaction of the large amount of HC, resulting in an excessively high temperature. turn into. As a result, the fuel efficiency is deteriorated and the NOx purification capacity is lowered.

【００４７】これに対し、本実施形態（１）では、ＨＣ
供給量Ｑは、前述したように上流側触媒温度Ｔａと下流
側触媒温度Ｔｂの双方を考慮した適切なＨＣ供給量Ｑａ
ｂに設定されるため、供給されるＨＣは、その大部分が
活性状態の高い上流側触媒１９でＮＯｘ浄化に用いら
れ、上流側触媒１９を通過して高温の下流側触媒２０に
流入するＨＣ量は少量である。これにより、ＮＯｘ浄化
率の高い上流側触媒１９で排気中のＮＯｘの大部分を浄
化し、高温の下流側触媒２０でのＨＣの反応を少なくし
て、下流側触媒２０が過昇温状態になることを防止す
る。これにより、必要最小限のＨＣの供給で、高いＮＯ
ｘ浄化能力を得ることができる。On the other hand, in this embodiment (1), HC
As described above, the supply amount Q is an appropriate HC supply amount Qa in consideration of both the upstream catalyst temperature Ta and the downstream catalyst temperature Tb.
b, most of the supplied HC is used for NOx purification by the upstream catalyst 19 having a high activation state, and flows into the high-temperature downstream catalyst 20 through the upstream catalyst 19. The amount is small. As a result, most of the NOx in the exhaust gas is purified by the upstream catalyst 19 having a high NOx purification rate, the reaction of HC in the high-temperature downstream catalyst 20 is reduced, and the downstream catalyst 20 is overheated. To prevent As a result, a high NO
x purification ability can be obtained.

【００４８】一方、図７は、上流側触媒１９の温度Ｔｃ
がＮＯｘ浄化上限温度Ｔ３付近で分布し、下流側触媒２
０の温度ＴｄがＮＯｘ浄化ピーク温度Ｔ２付近で分布し
ている場合を示している。このような温度分布は、ディ
ーゼルエンジン１０が中負荷の定常運転状態から比較的
高負荷の運転状態に移行したときに発生する。FIG. 7 shows the temperature Tc of the upstream side catalyst 19.
Are distributed near the NOx purification upper limit temperature T3, and the downstream side catalyst 2
A case where the temperature Td of 0 is distributed near the NOx purification peak temperature T2 is shown. Such a temperature distribution occurs when the diesel engine 10 shifts from a medium-load steady operation state to a relatively high-load operation state.

【００４９】この場合、基本ＨＣ供給量Ｑ１は、図８
（ａ）に示すように、上流側触媒温度Ｔｃに応じた比較
的少量の基本ＨＣ供給量Ｑ１ｃに設定され、補正ＨＣ供
給量Ｑ２は、図８（ｂ）に示すように、下流側触媒温度
Ｔｄに応じた多めの補正ＨＣ供給量Ｑ２ｄに設定され
る。ここで、図８（ａ），（ｂ）は、それぞれ図４
（ａ），（ｂ）のマップから現在のＮＯｘ排出量に対応
する曲線を抽出したものである。また、係数ｋ２は上流
側触媒温度Ｔｃ（＜３００℃）に応じてｋ２＝１に設定
される。これにより、後噴射により供給されるＨＣ供給
量Ｑは、Ｑ＝Ｑｃｄ＝Ｑ１ｃ＋Ｑ２ｄ（但しＱｃｄ＜Ｑ
max ）に設定される。In this case, the basic HC supply amount Q1 is as shown in FIG.
As shown in FIG. 8A, a relatively small basic HC supply amount Q1c corresponding to the upstream catalyst temperature Tc is set, and the corrected HC supply amount Q2 is set as shown in FIG. It is set to a larger corrected HC supply amount Q2d according to Td. Here, FIGS. 8A and 8B correspond to FIGS.
The curves corresponding to the current NOx emissions are extracted from the maps of (a) and (b). The coefficient k2 is set to k2 = 1 according to the upstream catalyst temperature Tc (<300 ° C.). Thus, the HC supply amount Q supplied by the post-injection is: Q = Qcd = Q1c + Q2d (where Qcd <Q
max).

【００５０】この際、もし、図９に示すように、補正Ｈ
Ｃ供給量の最大値Ｑ２max が基本ＨＣ供給量の最大値Ｑ
１max より大きい値に設定されたマップから、基本ＨＣ
供給量Ｑ１ｅと補正ＨＣ供給量Ｑ２ｆを算出し、ＨＣ供
給量ＱをＱ＝Ｑｅｆ＝Ｑ１ｅ＋Ｑ２ｆ（＞Ｑｃｄ）とす
ると、高温の上流側触媒１９には多量のＨＣを供給すべ
きでないにも拘らず、図１０（ｂ）に示すような多量の
ＨＣ（Ｑｅｆ）が供給されてしまうため、高温の上流側
触媒１９の温度は、多量のＨＣの反応熱により更に上昇
して過昇温状態になり、ほとんどＮＯｘを浄化できなく
なる。更に、上流側触媒１９から高温（＞Ｔ３）の排気
ガスが排出され、この排気ガスが下流側触媒２０に流入
するため、下流側触媒２０もＴ３近傍の温度まで上昇し
てＮＯｘ浄化率が低下してしまう。これにより、燃費の
悪化とＮＯｘ浄化能力の低下を招く。At this time, as shown in FIG.
The maximum value Q2max of the C supply amount is the maximum value Q of the basic HC supply amount.
From the map set to a value greater than 1max, the basic HC
The supply amount Q1e and the corrected HC supply amount Q2f are calculated. Assuming that the HC supply amount Q is Q = Qef = Q1e + Q2f (> Qcd), although a large amount of HC should not be supplied to the high-temperature upstream catalyst 19, Since a large amount of HC (Qef) is supplied as shown in FIG. 10 (b), the temperature of the high-temperature upstream catalyst 19 further rises due to a large amount of heat of reaction of HC, resulting in an excessively high temperature. , Almost no NOx can be purified. Further, high-temperature (> T3) exhaust gas is discharged from the upstream catalyst 19, and the exhaust gas flows into the downstream catalyst 20, so that the downstream catalyst 20 also rises to a temperature near T3 and the NOx purification rate decreases. Resulting in. As a result, the fuel efficiency is deteriorated and the NOx purification capacity is lowered.

【００５１】これに対し、本実施形態（１）では、基本
ＨＣ供給量Ｑ１と補正ＨＣ供給量Ｑ２のマップ特性（図
４及び図８参照）は、基本ＨＣ供給量の最大値Ｑ１max
が、補正ＨＣ供給量の最大値Ｑ２max よりも大きくなる
ように設定されているので、図７のような触媒温度分布
の場合には、ＨＣ供給量Ｑｃｄを少なくすることができ
る。これにより、高温の上流側触媒１９に多量のＨＣを
供給することを防止できるため、上流側触媒１９が過昇
温状態となることを防止できて、下流側触媒２０の温度
をＮＯｘ浄化ピーク温度Ｔ２付近に維持することがで
き、必要最小限のＨＣ供給で、高いＮＯｘ浄化率を得る
ことができる。On the other hand, in the present embodiment (1), the map characteristic of the basic HC supply amount Q1 and the corrected HC supply amount Q2 (see FIGS. 4 and 8) is the maximum value Q1max of the basic HC supply amount.
Is set to be larger than the maximum value Q2max of the corrected HC supply amount, so that in the case of the catalyst temperature distribution as shown in FIG. 7, the HC supply amount Qcd can be reduced. As a result, it is possible to prevent a large amount of HC from being supplied to the high-temperature upstream catalyst 19, so that it is possible to prevent the upstream catalyst 19 from being excessively heated, and to reduce the temperature of the downstream catalyst 20 to the NOx purification peak temperature. It can be maintained near T2, and a high NOx purification rate can be obtained with a minimum necessary HC supply.

【００５２】一方、図１１は、上流側触媒１９の温度Ｔ
ｇと下流側触媒２０の温度Ｔｈの双方がＮＯｘ浄化ピー
ク温度Ｔ２付近で分布している場合を示している。この
ような温度分布は、ディーゼルエンジン１０が中負荷の
定常運転状態のときに発生する。FIG. 11 shows the temperature T of the upstream side catalyst 19.
This shows a case where both the g and the temperature Th of the downstream side catalyst 20 are distributed near the NOx purification peak temperature T2. Such a temperature distribution occurs when the diesel engine 10 is in a steady operating state with a medium load.

【００５３】この場合、基本ＨＣ供給量Ｑ１は、図１２
（ａ）に示すように、上流側触媒温度Ｔｇに応じた多め
の基本ＨＣ供給量Ｑ１ｇ（最大値Ｑ１max に近い値）に
設定され、補正ＨＣ供給量Ｑ２は、図１２（ｂ）に示す
ように、下流側触媒温度Ｔｈに応じた多めの補正ＨＣ供
給量Ｑ２ｈ（最大値Ｑ２max に近い値）に設定される。
ここで、図１２（ａ），（ｂ）は、それぞれ図４の
（ａ），（ｂ）のマップから現在のＮＯｘ排出量に対応
する曲線を抽出したものである。また、係数ｋ２は、上
流側触媒温度Ｔｇ（＜３００℃）に応じてｋ２＝１に設
定される。これにより、仮のＨＣ供給量Ｑ０は、Ｑ０＝
Ｑｇｈ＝Ｑ１ｇ＋Ｑ２ｈとかなり大きな値となり、仮の
ＨＣ供給量Ｑ０は、上限ＨＣ供給量Ｑmax （＝Ｑ１max
）よりも大きな値となる（図１４参照）。In this case, the basic HC supply amount Q1
As shown in FIG. 12A, the basic HC supply amount Q1g (a value close to the maximum value Q1max) corresponding to the upstream catalyst temperature Tg is set to a relatively large value, and the corrected HC supply amount Q2 is set as shown in FIG. Then, a larger corrected HC supply amount Q2h (a value close to the maximum value Q2max) corresponding to the downstream catalyst temperature Th is set.
Here, FIGS. 12 (a) and 12 (b) are obtained by extracting curves corresponding to the current NOx emission amount from the maps of FIGS. 4 (a) and 4 (b), respectively. The coefficient k2 is set to k2 = 1 according to the upstream catalyst temperature Tg (<300 ° C.). As a result, the provisional HC supply amount Q0 becomes Q0 =
Qgh = Q1g + Q2h, which is a considerably large value, and the provisional HC supply amount Q0 becomes the upper limit HC supply amount Qmax (= Q1max
) (See FIG. 14).

【００５４】この際、もし、この仮のＨＣ供給量Ｑｇｈ
を、そのままＨＣ供給量として採用すると、基本ＨＣ供
給量の最大値Ｑ１max を大きく上回る多量のＨＣが供給
されるため、図１３（ｂ）に示すように、ＨＣの反応熱
により上流側触媒１９の温度がＮＯｘ浄化上限温度Ｔ３
付近まで上昇してＮＯｘ浄化率が低下する。更に、上流
側触媒１９から多量のＨＣを含んだ高温の排気ガスが排
出され、この排気ガスが下流側触媒２０に流入するた
め、下流側触媒２０が排気ガスの熱とＨＣの反応熱によ
り過昇温状態となり、下流側触媒２０ではＮＯｘの浄化
がほとんど行われなくなる。これにより、燃費の悪化と
ＮＯｘ浄化能力の低下を招く。At this time, if the provisional HC supply amount Qgh
Is employed as the HC supply amount, a large amount of HC is supplied, which greatly exceeds the maximum value Q1max of the basic HC supply amount. Therefore, as shown in FIG. Temperature is NOx purification upper limit temperature T3
It rises to the vicinity and the NOx purification rate decreases. Further, high-temperature exhaust gas containing a large amount of HC is discharged from the upstream catalyst 19, and this exhaust gas flows into the downstream catalyst 20, so that the downstream catalyst 20 is excessively heated by the heat of the exhaust gas and the reaction heat of HC. As a result, the downstream side catalyst 20 hardly purifies NOx. As a result, the fuel efficiency is deteriorated and the NOx purification capacity is lowered.

【００５５】これに対し、本実施形態（１）では、仮の
ＨＣ供給量Ｑｇｈを上限ＨＣ供給量Ｑmax でガード処理
するので、上流側触媒１９と下流側触媒２０の温度が共
にＮＯｘ浄化ピーク温度Ｔ２付近であっても、ＨＣ供給
量Ｑを上限ＨＣ供給量Ｑmax（＝Ｑ１max ）以下に抑え
ることができる。この結果、図１１のような触媒温度分
布の場合には、上流側触媒１９の浄化能力を７〜８割程
度に抑えて、図１３（ａ）に示すように、上流側触媒１
９からの流出ガス温度をＴ２とＴ３の間に抑えることが
でき、下流側触媒２０の温度がＮＯｘ浄化上限温度Ｔ３
以上に過昇温することを防止できて、上流側触媒１９を
通過したＨＣにより下流側触媒２０でもＮＯｘを浄化す
ることができる。これにより、上流側触媒１９と下流側
触媒２０の双方を有効に使用して、必要最小限のＨＣ供
給で高いＮＯｘ浄化能力を得ることができる。On the other hand, in the present embodiment (1), since the provisional HC supply amount Qgh is guarded by the upper limit HC supply amount Qmax, the temperatures of the upstream catalyst 19 and the downstream catalyst 20 are both the NOx purification peak temperature. Even near T2, the HC supply amount Q can be suppressed to the upper limit HC supply amount Qmax (= Q1max) or less. As a result, in the case of the catalyst temperature distribution as shown in FIG. 11, the purification capacity of the upstream catalyst 19 is suppressed to about 70 to 80%, and as shown in FIG.
9 can be suppressed between T2 and T3, and the temperature of the downstream side catalyst 20 becomes NOx purification upper limit temperature T3.
As described above, excessive heating can be prevented, and NOx can be purified by the downstream catalyst 20 by the HC that has passed through the upstream catalyst 19. As a result, both the upstream catalyst 19 and the downstream catalyst 20 can be effectively used, and a high NOx purification ability can be obtained with a minimum necessary HC supply.

【００５６】図１５は、本実施形態（１）の噴射制御プ
ログラムによりＨＣ供給量を制御した場合と、上流側触
媒１９と下流側触媒２０の流出ガス温度の高い方を上流
側及び下流側触媒１９，２０の双方の活性状態を代表す
る温度としてＨＣ供給量を制御した場合（比較例１，
２）とで、モード走行時の燃費及びＮＯｘ浄化率を比較
したものである。比較例１と比較例２は、ＨＣ供給量の
マップ特性が異なり、比較例１の方が比較例２よりもＨ
Ｃ供給量が多くなるように設定されている。FIG. 15 shows a case where the HC supply amount is controlled by the injection control program of the embodiment (1) and a case where the outflow gas temperatures of the upstream catalyst 19 and the downstream catalyst 20 are higher. When the HC supply rate is controlled as a temperature representative of both the active states 19 and 20 (Comparative Example 1,
2) and a comparison of fuel efficiency and NOx purification rate during mode running. Comparative Example 1 and Comparative Example 2 differ in the map characteristic of the HC supply amount, and Comparative Example 1 has a higher H value than Comparative Example 2.
The C supply amount is set to be large.

【００５７】図１５から明らかなように、本実施形態
（１）では、比較例１，２に対して同一燃費で比較する
と、ＮＯｘ浄化率が約１．５倍から２倍に向上している
ことが分かる。As is apparent from FIG. 15, in this embodiment (1), when compared with Comparative Examples 1 and 2 at the same fuel efficiency, the NOx purification rate is improved from about 1.5 times to 2 times. You can see that.

【００５８】また、図１６は、本実施形態（１）と比較
例１について、１５モード前半の上流側触媒１９の流入
ガス温度に対する上流側触媒１９及び下流側触媒２０の
触媒中心温度の挙動を比較したタイムチャートである。FIG. 16 shows the behavior of the catalyst center temperature of the upstream catalyst 19 and the downstream catalyst 20 with respect to the inflow gas temperature of the upstream catalyst 19 in the first half of the fifteen mode for the embodiment (1) and the comparative example 1. It is a time chart which compared.

【００５９】図１６から明らかなように、上流側触媒１
９、下流側触媒２０いずれの場合も、本実施形態（１）
の方が比較例１よりも過昇温が抑制されている。更に、
本実施形態（１）では、下流側触媒２０の温度をＮＯｘ
浄化ピーク温度Ｔ２付近に維持できる時間が長くなり、
ＮＯｘ浄化率が高くなることが分かる。As is apparent from FIG. 16, the upstream catalyst 1
9, the embodiment (1) in any case of the downstream side catalyst 20.
The excessive temperature rise is more suppressed in Comparative Example 1 than in Comparative Example 1. Furthermore,
In the embodiment (1), the temperature of the downstream side catalyst 20 is set to NOx
The time that can be maintained near the purification peak temperature T2 becomes longer,
It can be seen that the NOx purification rate increases.

【００６０】以上説明した本実施形態（１）では、上流
側触媒１９と下流側触媒２０の双方の活性状態を考慮し
てＨＣ供給量を設定できるため、ＨＣの過剰供給により
上流側及び下流側触媒１９，２０が過昇温状態になるこ
とを防止でき、必要最小限のＨＣ供給量で排気ガス中の
ＮＯｘを効率良く浄化することができて、ＮＯｘ浄化率
と燃費を向上させることができる。しかも、本実施形態
（１）では、前記公知例（特開平８−２８１０６９号公
報）のように、触媒の個数と同数のＨＣ供給装置を設け
る必要がなく、装置の構成を簡素化できて、装置を小型
化・低コスト化できるメリットもある。In the above-described embodiment (1), the amount of HC supply can be set in consideration of the activation state of both the upstream catalyst 19 and the downstream catalyst 20, and therefore the excess supply of HC causes the upstream and downstream sides to be set. The catalysts 19 and 20 can be prevented from being in an excessively high temperature state, NOx in exhaust gas can be efficiently purified with a minimum necessary amount of HC supply, and the NOx purification rate and fuel efficiency can be improved. . Moreover, in the present embodiment (1), it is not necessary to provide the same number of HC supply devices as the number of catalysts as in the known example (Japanese Patent Laid-Open No. 8-28069), and the configuration of the device can be simplified. There is also an advantage that the device can be reduced in size and cost.

【００６１】［実施形態（２）］前記実施形態（１）で
は、補正ＨＣ供給量Ｑ２のマップ特性は、図４（ｂ）、
図６（ｂ）等に示すように、補正ＨＣ供給量Ｑ２が触媒
温度により変化するＮＯｘ浄化率に対応して増減するよ
うに設定されていたが、本実施形態（２）では、図１７
に示すように、補正ＨＣ供給量Ｑ２の触媒温度に対する
増減特性を、ＮＯｘ浄化ピーク温度Ｔ２以上の領域での
触媒温度上昇による減少割合が、ＮＯｘ浄化ピーク温度
Ｔ２以下の領域での触媒温度上昇による増加割合よりも
大きくなるように設定している。[Embodiment (2)] In the embodiment (1), the map characteristic of the corrected HC supply amount Q2 is as shown in FIG.
As shown in FIG. 6B and the like, the correction HC supply amount Q2 is set so as to increase or decrease in accordance with the NOx purification rate that changes according to the catalyst temperature. However, in the present embodiment (2), FIG.
As shown in the graph, the increasing / decreasing characteristic of the corrected HC supply amount Q2 with respect to the catalyst temperature depends on the catalyst temperature increase in the region where the NOx purification peak temperature T2 or lower indicates the decrease rate due to the catalyst temperature increase in the region or higher. It is set to be larger than the increase rate.

【００６２】更に、前記実施形態（１）では、上限ＨＣ
供給量Ｑmax を基本ＨＣ供給量の最大値Ｑ１max に固定
したが、本実施形態（２）では、図１８に示すように、
上限ＨＣ供給量Ｑmax を上流側触媒温度に応じて変化さ
せる。具体的には、上流側触媒温度がＮＯｘ浄化ピーク
温度Ｔ２のときに上限ＨＣ供給量Ｑmax が最大となり
（上限ＨＣ供給量Ｑmax ＝基本ＨＣ供給量最大値Ｑ１ma
x ）、上流側触媒温度がＮＯｘ浄化ピーク温度Ｔ２から
離れるに従って、上限ＨＣ供給量Ｑmax が小さくなるよ
うに設定している。その他は、前記実施形態（１）と同
じである。Further, in the embodiment (1), the upper limit HC
Although the supply amount Qmax is fixed to the maximum value Q1max of the basic HC supply amount, in the present embodiment (2), as shown in FIG.
The upper limit HC supply amount Qmax is changed according to the upstream catalyst temperature. Specifically, when the upstream catalyst temperature is the NOx purification peak temperature T2, the upper limit HC supply amount Qmax becomes maximum (the upper limit HC supply amount Qmax = the basic HC supply amount maximum value Q1ma).
x), the upper limit HC supply amount Qmax is set to decrease as the upstream catalyst temperature moves away from the NOx purification peak temperature T2. Others are the same as the embodiment (1).

【００６３】本実施形態（２）では、下流側触媒２０の
温度がＮＯｘ浄化ピーク温度Ｔ２を越えて上昇すると、
補正ＨＣ供給量Ｑ２が急激に低減されて、ＮＯｘ浄化上
限温度Ｔ３付近の下流側触媒２０に供給されるＨＣ量が
低減され、下流側触媒２０が過昇温状態となることがよ
り効果的に抑えられる。このため、下流側触媒２０の温
度をＮＯｘ浄化温度範囲（Ｔ１〜Ｔ３）内に維持する時
間をより長くすることができ、より少ないＨＣ供給量
で、より高いＮＯｘ浄化率を得ることができる。In this embodiment (2), when the temperature of the downstream side catalyst 20 rises above the NOx purification peak temperature T2,
The corrected HC supply amount Q2 is sharply reduced, the HC amount supplied to the downstream catalyst 20 near the NOx purification upper limit temperature T3 is reduced, and the downstream catalyst 20 is more effectively heated. Can be suppressed. Therefore, the time for maintaining the temperature of the downstream side catalyst 20 within the NOx purification temperature range (T1 to T3) can be made longer, and a higher NOx purification rate can be obtained with a smaller HC supply amount.

【００６４】更に、本実施形態（２）では、図１８に示
すように上限ＨＣ供給量Ｑmax が上流側触媒温度に応じ
て変化するため、上流側触媒１９の低温時に、ＨＣ供給
量を少なくして上流側触媒１９ヘのＨＣ吸着量を適正範
囲内にすることができ、上流側触媒１９のＨＣ被毒（Ｈ
Ｃが触媒表面上を覆ってしまう状態）を抑制することが
できる。また、上流側触媒１９の高温時には、ＨＣ供給
量を少なくしてＨＣ反応量を少なくでき、上流側触媒１
９の過昇温を防止することができる。いずれの場合も、
少ないＨＣ供給量で、ＮＯｘ浄化率を向上させることが
できる。Further, in the present embodiment (2), the upper limit HC supply amount Qmax changes according to the upstream catalyst temperature as shown in FIG. As a result, the amount of HC adsorbed on the upstream catalyst 19 can be kept within an appropriate range, and HC poisoning (H
The state in which C covers the catalyst surface) can be suppressed. When the temperature of the upstream side catalyst 19 is high, the amount of HC reaction can be reduced by reducing the amount of HC supply, and the upstream side catalyst 1
9 can be prevented from overheating. In either case,
The NOx purification rate can be improved with a small HC supply amount.

【００６５】以上説明したように、本実施形態（２）に
よれば、触媒１９，２０へのＨＣ供給による燃費悪化
を、前記実施形態（１）よりも更に低減しながら、ＮＯ
ｘ浄化性能を向上させることができる（図１５参照）。As described above, according to the present embodiment (2), the deterioration of fuel efficiency due to the supply of HC to the catalysts 19 and 20 is further reduced as compared with the above-described embodiment (1).
x Purification performance can be improved (see FIG. 15).

【００６６】尚、基本ＨＣ供給量Ｑ１の増減特性につい
ても、ＮＯｘ浄化ピーク温度以上の領域での減少割合が
ＮＯｘ浄化ピーク温度以下の領域での増加割合よりも大
きくなるように設定しても良い。このようにすれば、上
流側触媒１９がＮＯｘ浄化ピーク温度Ｔ２以上の領域で
は、触媒温度が高くなるほど、基本ＨＣ供給量Ｑ１が急
激に低減されるため、上流側触媒１９へのＨＣ供給量が
急激に低減されて、上流側触媒１９でのＨＣの反応熱が
急激に低減される。これにより、上流側触媒１９が過昇
温状態となることを防止でき、上流側触媒１９の流出ガ
ス温度の上昇を抑えることができ、下流側触媒２０が過
昇温状態となることも防止できる。この結果、より少な
いＨＣ供給量で優れたＮＯｘ浄化性能を得ることができ
る。The increase / decrease characteristics of the basic HC supply amount Q1 may be set so that the rate of decrease in the region above the NOx purification peak temperature is greater than that in the region below the NOx purification peak temperature. . In this manner, in a region where the upstream catalyst 19 is equal to or higher than the NOx purification peak temperature T2, the basic HC supply amount Q1 is sharply reduced as the catalyst temperature increases, so that the HC supply amount to the upstream catalyst 19 is reduced. As a result, the reaction heat of HC in the upstream catalyst 19 is rapidly reduced. Thus, the upstream catalyst 19 can be prevented from being in an excessively high temperature state, the rise in the outflow gas temperature of the upstream catalyst 19 can be suppressed, and the downstream catalyst 20 can also be prevented from being in an excessively high temperature state. . As a result, excellent NOx purification performance can be obtained with a smaller HC supply amount.

【００６７】［実施形態（３）］本実施形態（３）で
は、図２に示すように、ＮＯｘ浄化率に応じて第１乃至
第４の温度ゾーンに区分し、上流側触媒１９の触媒温度
が属する温度ゾーンと、下流側触媒２０の触媒温度が属
する温度ゾーンとの組み合わせにより基本ＨＣ供給量を
補正してＨＣ供給量を決定する。ここで、第１の温度ゾ
ーンは、ＮＯｘ浄化下限温度Ｔ１未満の領域（ＮＯｘ浄
化率が低いレベルで推移する領域）、第２の温度ゾーン
は、ＮＯｘ浄化下限温度Ｔ１からＮＯｘ浄化ピーク温度
Ｔ２までの領域（ＮＯｘ浄化率が温度と共に上昇する領
域）、第３の温度ゾーンは、ＮＯｘ浄化ピーク温度Ｔ２
からＮＯｘ浄化上限温度Ｔ３までの領域（ＮＯｘ浄化率
が温度と共に下降する領域）、第４の温度ゾーンは、Ｎ
Ｏｘ浄化上限温度Ｔ３以上の領域（ＮＯｘ浄化率が低い
レベルで推移する領域）である。システム構成は、前記
実施形態（１）で説明した図１と同じである。[Embodiment (3)] In this embodiment (3), as shown in FIG. 2, the catalyst is divided into first to fourth temperature zones according to the NOx purification rate, And the temperature zone to which the catalyst temperature of the downstream-side catalyst 20 belongs, and the basic HC supply amount is corrected to determine the HC supply amount. Here, the first temperature zone is a region below the NOx purification lower limit temperature T1 (region where the NOx purification rate changes at a low level), and the second temperature zone is from the NOx purification lower limit temperature T1 to the NOx purification peak temperature T2. (A region where the NOx purification rate rises with temperature), the third temperature zone is the NOx purification peak temperature T2
The region from NO to the NOx purification upper limit temperature T3 (the region where the NOx purification rate decreases with temperature), the fourth temperature zone is N
This is a region above the Ox purification upper limit temperature T3 (region where the NOx purification rate changes at a low level). The system configuration is the same as that in FIG. 1 described in the embodiment (1).

【００６８】本実施形態（３）では、図１９及び図２０
に示す噴射制御プログラムをＥＣＵ２３にて各気筒の噴
射タイミング毎に実行することで、次のようにしてＨＣ
供給量を決定する。本プログラムが起動されると、ステ
ップ２０１〜２０４で、前記実施形態（１）で説明した
図３のステップ１０１〜１０４と同じく、アクセルセン
サ２５、エンジン回転数センサ２４及び排気温度センサ
２１，２２から出力される信号を読み込んで、主燃料噴
射量を算出し、ディーゼルエンジン１０から排出される
ＮＯｘ量を推定すると共に、上流側触媒温度Ｔａａ及び
下流側触媒温度Ｔｂｂを判定する。In this embodiment (3), FIGS.
The ECU 23 executes the injection control program shown in FIG.
Determine the supply. When this program is started, in steps 201 to 204, the accelerator sensor 25, the engine speed sensor 24, and the exhaust temperature sensors 21 and 22 are used in the same manner as in steps 101 to 104 of FIG. The output signal is read, the main fuel injection amount is calculated, the NOx amount discharged from the diesel engine 10 is estimated, and the upstream catalyst temperature Taa and the downstream catalyst temperature Tbb are determined.

【００６９】この後、ステップ２０５で、図４（ａ）に
示す上流側触媒温度とＮＯｘ排出量とをパラメータとす
る基本ＨＣ供給量Ｑ１のマップを検索し、現在の上流側
触媒温度ＴａａとＮＯｘ排出量に応じた基本ＨＣ供給量
Ｑ１１を求める。次のステップ２０６で、第１の温度ゾ
ーンと第２の温度ゾーンの境界温度（つまりＮＯｘ浄化
下限温度）であるＴ１，第２の温度ゾーンと第３の温度
ゾーンの境界温度（つまりＮＯｘ浄化ピーク温度）であ
るＴ２，第３の温度ゾーンと第４の温度ゾーンの境界温
度（つまりＮＯｘ浄化上限温度）であるＴ３を読み込
む。これらＴ１〜Ｔ３は、上流側触媒温度Ｔａａと下流
側触媒温度Ｔｂｂが、どの温度ゾーンに属するのかの判
定に用いられる。After that, in step 205, a map of the basic HC supply amount Q1 using the upstream catalyst temperature and the NOx emission amount as parameters as shown in FIG. 4A is searched, and the current upstream catalyst temperature Taa and NOx A basic HC supply amount Q11 according to the discharge amount is obtained. In the next step 206, T1, which is the boundary temperature between the first temperature zone and the second temperature zone (that is, the NOx purification lower limit temperature), and the boundary temperature between the second temperature zone and the third temperature zone (that is, the NOx purification peak) T2, which is the temperature), and T3, which is the boundary temperature between the third temperature zone and the fourth temperature zone (that is, the NOx purification upper limit temperature). These T1 to T3 are used to determine to which temperature zone the upstream catalyst temperature Taa and the downstream catalyst temperature Tbb belong.

【００７０】この後、ステップ２０７以降の処理で、上
流側触媒温度Ｔａａと下流側触媒温度ＴｂｂをＴ１，Ｔ
２，Ｔ３と比較して、どの温度ゾーンに属するか判定
し、上流側触媒温度Ｔａａが属する温度ゾーンと、下流
側触媒温度Ｔｂｂが属する温度ゾーンとの組み合わせに
より基本ＨＣ供給量Ｑ１１を補正してＨＣ供給量を決定
する。Thereafter, in the processing after step 207, the upstream catalyst temperature Taa and the downstream catalyst temperature Tbb are set to T1 and T1.
2 and T3 to determine which temperature zone it belongs to, and correct the basic HC supply amount Q11 by a combination of a temperature zone to which the upstream catalyst temperature Taa belongs and a temperature zone to which the downstream catalyst temperature Tbb belongs. Determine the amount of HC supply.

【００７１】具体的には、上流側触媒温度Ｔａａと下流
側触媒温度Ｔｂｂが共に第１の温度ゾーン（Ｔａａ＜Ｔ
１且つＴｂｂ＜Ｔ１）の場合には、ステップ２０７→２
０８→２０９へと進み、ステップ２０５で算出した基本
ＨＣ供給量Ｑ１１に対する増量補正分として補正ＨＣ供
給量Ｑ２２を、上流側触媒温度Ｔａａに応じて例えば１
０００〜２０００ｐｐｍＣに設定し、所定期間（例えば
１分間）のみ増量補正する。Specifically, both the upstream catalyst temperature Taa and the downstream catalyst temperature Tbb are in the first temperature zone (Taa <T
1 and Tbb <T1), step 207 → 2
08 → 209, and the corrected HC supply amount Q22 as an increase correction amount to the basic HC supply amount Q11 calculated in step 205 is set to, for example, 1 according to the upstream side catalyst temperature Taa.
It is set to 2,000 to 2,000 ppmC, and the increase correction is performed only for a predetermined period (for example, one minute).

【００７２】上流側触媒温度Ｔａａが第１の温度ゾーン
（Ｔａａ＜Ｔ１）で、下流側触媒温度Ｔｂｂが第２の温
度ゾーン（Ｔ１≦Ｔｂｂ＜Ｔ２）の場合には、ステップ
２０７→２０８→２１０→２１１へと進み、補正ＨＣ供
給量Ｑ２２を上流側触媒温度Ｔａａに応じて例えば１０
００〜２０００ｐｐｍＣに設定し、所定期間（例えば１
分間）後に、例えば２００〜１０００ｐｐｍＣに減量す
る。If the upstream catalyst temperature Taa is in the first temperature zone (Taa <T1) and the downstream catalyst temperature Tbb is in the second temperature zone (T1 ≦ Tbb <T2), steps 207 → 208 → 210 → The process proceeds to 211, and the corrected HC supply amount Q22 is set to, for example, 10
00 to 2000 ppmC for a predetermined period (for example, 1
Minutes), the weight is reduced to, for example, 200 to 1000 ppmC.

【００７３】上流側触媒温度Ｔａａが第１の温度ゾーン
（Ｔａａ＜Ｔ１）で、下流側触媒温度Ｔｂｂが第３の温
度ゾーン（Ｔ２≦Ｔｂｂ＜Ｔ３）の場合には、ステップ
２０７→２０８→２１０→２１２→２１３へと進み、上
記ステップ２１１と同じく、補正ＨＣ供給量Ｑ２２を上
流側触媒温度Ｔａａに応じて例えば１０００〜２０００
ｐｐｍＣに設定し、所定期間（例えば１分間）後に、例
えば２００〜１０００ｐｐｍＣに減量する。ここで、補
正ＨＣ供給量Ｑ２２は、下流側触媒温度ＴｂｂがＮＯｘ
浄化上限温度Ｔ３近傍で少量となるように設定される。If the upstream catalyst temperature Taa is in the first temperature zone (Taa <T1) and the downstream catalyst temperature Tbb is in the third temperature zone (T2 ≦ Tbb <T3), steps 207 → 208 → 210 → 212 → 213, and the corrected HC supply amount Q22 is set to, for example, 1000 to 2000 in accordance with the upstream side catalyst temperature Taa, similarly to the step 211.
ppmC, and after a predetermined period (for example, 1 minute), the amount is reduced to, for example, 200 to 1000 ppmC. Here, the corrected HC supply amount Q22 is such that the downstream catalyst temperature Tbb is NOx
It is set so that the amount becomes small near the purification upper limit temperature T3.

【００７４】尚、上記ステップ２１１，２１３では、補
正ＨＣ供給量Ｑ２２を所定期間経過後に減量するように
しているが、時間の経過と共に徐々に減量するようにし
ても良い。In steps 211 and 213, the corrected HC supply amount Q22 is decreased after the elapse of a predetermined period, but may be gradually decreased as time elapses.

【００７５】上流側触媒温度Ｔａａが第１の温度ゾーン
（Ｔａａ＜Ｔ１）で、下流側触媒温度Ｔｂｂが第４の温
度ゾーン（Ｔｂｂ≧Ｔ３）の場合には、ステップ２０７
→２０８→２１０→２１２→２１４へと進み、補正ＨＣ
供給量Ｑ２２を０に設定して、基本ＨＣ供給量Ｑ１１に
対する増量補正を行わない。If the upstream catalyst temperature Taa is in the first temperature zone (Taa <T1) and the downstream catalyst temperature Tbb is in the fourth temperature zone (Tbb ≧ T3), step 207 is executed.
→ 208 → 210 → 212 → 214
The supply amount Q22 is set to 0, and the increase correction for the basic HC supply amount Q11 is not performed.

【００７６】上流側触媒温度Ｔａａが第２の温度ゾーン
（Ｔ１≦Ｔａａ＜Ｔ２）で、下流側触媒温度Ｔｂｂが第
１の温度ゾーン（Ｔｂｂ＜Ｔ１）の場合には、ステップ
２０７→２１５→２１６→２１７へと進み、補正ＨＣ供
給量Ｑ２２を例えば１０００ｐｐｍＣに設定し、この増
量補正を所定期間（例えば１分間）のみ実行する。If the upstream catalyst temperature Taa is in the second temperature zone (T1 ≦ Taa <T2) and the downstream catalyst temperature Tbb is in the first temperature zone (Tbb <T1), steps 207 → 215 → 216 The process proceeds to 217, where the corrected HC supply amount Q22 is set to, for example, 1000 ppmC, and the increase correction is executed only for a predetermined period (for example, one minute).

【００７７】上流側触媒温度Ｔａａと下流側触媒温度Ｔ
ｂｂが共に第２の温度ゾーン（Ｔ１≦Ｔａａ＜Ｔ２且つ
Ｔ１≦Ｔｂｂ＜Ｔ２）の場合には、ステップ２０７→２
１５→２１６→２１８→２１９へと進み、補正ＨＣ供給
量Ｑ２２を下流側触媒温度Ｔｂｂに応じて例えば５００
〜２０００ｐｐｍＣに設定する。ここで、補正ＨＣ供給
量Ｑ２２は、下流側触媒温度ＴｂｂがＮＯｘ浄化ピーク
温度Ｔ２近傍になるほど増加するように設定される。The upstream catalyst temperature Taa and the downstream catalyst temperature T
If both bb are in the second temperature zone (T1 ≦ Taa <T2 and T1 ≦ Tbb <T2), step 207 → 2
The flow proceeds from 15 → 216 → 218 → 219, and the corrected HC supply amount Q22 is set to, for example, 500 in accordance with the downstream side catalyst temperature Tbb.
Set to ~ 2000 ppmC. Here, the corrected HC supply amount Q22 is set so as to increase as the downstream catalyst temperature Tbb approaches the NOx purification peak temperature T2.

【００７８】上流側触媒温度Ｔａａが第２の温度ゾーン
（Ｔ１≦Ｔａａ＜Ｔ２）で、下流側触媒温度Ｔｂｂが第
３の温度ゾーン（Ｔ２≦Ｔｂｂ＜Ｔ３）の場合には、ス
テップ２０７→２１５→２１６→２１８→２２０→２２
１へと進み、補正ＨＣ供給量Ｑ２２を下流側触媒温度Ｔ
ｂｂに応じて例えば５００〜２０００ｐｐｍＣに設定す
る。ここで、補正ＨＣ供給量Ｑ２２は、下流側触媒温度
ＴｂｂがＮＯｘ浄化上限温度Ｔ３近傍で少量になるよう
に設定される。If the upstream catalyst temperature Taa is in the second temperature zone (T1 ≦ Taa <T2) and the downstream catalyst temperature Tbb is in the third temperature zone (T2 ≦ Tbb <T3), steps 207 → 215 → 216 → 218 → 220 → 22
1 to reduce the corrected HC supply amount Q22 to the downstream catalyst temperature T.
For example, it is set to 500 to 2000 ppmC according to bb. Here, the corrected HC supply amount Q22 is set such that the downstream catalyst temperature Tbb becomes small near the NOx purification upper limit temperature T3.

【００７９】上流側触媒温度Ｔａａが第２の温度ゾーン
（Ｔ１≦Ｔａａ＜Ｔ２）で、下流側触媒温度Ｔｂｂが第
４の温度ゾーン（Ｔｂｂ≧Ｔ３）の場合には、ステップ
２０７→２１５→２１６→２１８→２２０→２２２へと
進み、補正ＨＣ供給量Ｑ２２を０に設定して、基本ＨＣ
供給量Ｑ１１に対する増量補正を行わない。If the upstream catalyst temperature Taa is in the second temperature zone (T1 ≦ Taa <T2) and the downstream catalyst temperature Tbb is in the fourth temperature zone (Tbb ≧ T3), steps 207 → 215 → 216 → 218 → 220 → 222, the corrected HC supply amount Q22 is set to 0, and the basic HC
No increase correction is performed on the supply amount Q11.

【００８０】上流側触媒温度Ｔａａが第３の温度ゾーン
（Ｔ２≦Ｔａａ＜Ｔ３）で、下流側触媒温度Ｔｂｂが第
１の温度ゾーン（Ｔｂｂ＜Ｔ１）の場合には、ステップ
２０７→２１５→２２３→２２４→２２５へと進み、補
正ＨＣ供給量Ｑ２２を例えば５００ｐｐｍＣに設定す
る。If the upstream catalyst temperature Taa is in the third temperature zone (T2 ≦ Taa <T3) and the downstream catalyst temperature Tbb is in the first temperature zone (Tbb <T1), steps 207 → 215 → 223 The process proceeds from 224 to 225, and the corrected HC supply amount Q22 is set to, for example, 500 ppmC.

【００８１】上流側触媒温度Ｔａａが第３の温度ゾーン
（Ｔ２≦Ｔａａ＜Ｔ３）で、下流側触媒温度Ｔｂｂが第
２の温度ゾーン（Ｔ１≦Ｔｂｂ＜Ｔ２）の場合には、ス
テップ２０７→２１５→２２３→２２４→２２６→２２
７へと進み、補正ＨＣ供給量Ｑ２２を下流側触媒温度Ｔ
ｂｂに応じて例えば５００〜２０００ｐｐｍＣに設定す
る。ここで、補正ＨＣ供給量Ｑ２２は、下流側触媒温度
ＴｂｂがＮＯｘ浄化ピーク温度Ｔ２近傍になるほど増加
するように設定される。If the upstream catalyst temperature Taa is in the third temperature zone (T2 ≦ Taa <T3) and the downstream catalyst temperature Tbb is in the second temperature zone (T1 ≦ Tbb <T2), steps 207 → 215 → 223 → 224 → 226 → 22
7, the corrected HC supply amount Q22 is changed to the downstream side catalyst temperature T.
For example, it is set to 500 to 2000 ppmC according to bb. Here, the corrected HC supply amount Q22 is set so as to increase as the downstream catalyst temperature Tbb approaches the NOx purification peak temperature T2.

【００８２】上流側触媒温度Ｔａａと下流側触媒温度Ｔ
ｂｂが共に第３の温度ゾーン（Ｔ２≦Ｔａａ＜Ｔ３且つ
Ｔ２≦Ｔｂｂ＜Ｔ３）の場合には、ステップ２０７→２
１５→２２３→２２４→２２６→２２８→２２９へと進
み、補正ＨＣ供給量Ｑ２２を下流側触媒温度Ｔｂｂに応
じて例えば３００〜１５００ｐｐｍＣに設定する。ここ
で、補正ＨＣ供給量Ｑ２２は、上記ステップ２２７で設
定される補正ＨＣ供給量よりも小さく、且つ、下流側触
媒温度ＴｂｂがＮＯｘ浄化上限温度Ｔ３近傍で少量にな
るように設定される。この場合、補正ＨＣ供給量Ｑ２２
を０に設定して、基本ＨＣ供給量Ｑ１１に対する増量補
正を行わないようにしても良い。The upstream catalyst temperature Taa and the downstream catalyst temperature T
If both bb are in the third temperature zone (T2 ≦ Taa <T3 and T2 ≦ Tbb <T3), step 207 → 2
The flow proceeds from 15 to 223 to 224 to 226 to 228 to 229, and the corrected HC supply amount Q22 is set to, for example, 300 to 1500 ppmC according to the downstream catalyst temperature Tbb. Here, the corrected HC supply amount Q22 is set so as to be smaller than the corrected HC supply amount set in step 227, and to make the downstream catalyst temperature Tbb small near the NOx purification upper limit temperature T3. In this case, the corrected HC supply amount Q22
May be set to 0 so that the increase correction for the basic HC supply amount Q11 is not performed.

【００８３】上流側触媒温度Ｔａａが第３の温度ゾーン
（Ｔ２≦Ｔａａ＜Ｔ３）で、下流側触媒温度Ｔｂｂが第
４の温度ゾーン（Ｔｂｂ≧Ｔ３）の場合には、ステップ
２０７→２１５→２２３→２２４→２２６→２２８→２
３０へと進み、補正ＨＣ供給量Ｑ２２を０に設定して、
基本ＨＣ供給量Ｑ１１に対する増量補正を行わない。If the upstream catalyst temperature Taa is in the third temperature zone (T2 ≦ Taa <T3) and the downstream catalyst temperature Tbb is in the fourth temperature zone (Tbb ≧ T3), steps 207 → 215 → 223 → 224 → 226 → 228 → 2
30 and sets the corrected HC supply amount Q22 to 0,
No increase correction is performed on the basic HC supply amount Q11.

【００８４】上流側触媒温度Ｔａａが第４の温度ゾーン
（Ｔａａ≧Ｔ３）の場合には、ステップ２０７→２１５
→２２３→２３１へと進み、下流側触媒温度Ｔｂｂがい
ずれの温度ゾーンであっても、補正ＨＣ供給量Ｑ２２を
０に設定して、基本ＨＣ供給量Ｑ１１に対する増量補正
を行わない。If the upstream catalyst temperature Taa is in the fourth temperature zone (Taa ≧ T3), the process proceeds from step 207 to step 215
The flow proceeds from 223 to 231 and the correction HC supply amount Q22 is set to 0 and the increase correction for the basic HC supply amount Q11 is not performed in any temperature zone of the downstream side catalyst temperature Tbb.

【００８５】以上のようにして、上流側触媒温度Ｔａａ
が属する温度ゾーンと、下流側触媒温度Ｔｂｂが属する
温度ゾーンとの組み合わせにより、図２１に示すように
基本ＨＣ供給量Ｑ１１を補正してＨＣ供給量を決定した
後、ステップ２３２に進み、基本ＨＣ供給量Ｑ１１に補
正ＨＣ供給量Ｑ２２を加算して、上流側触媒１９と下流
側触媒２０の双方の活性状態（触媒温度）を考慮したＨ
Ｃ供給量ＱＱを算出する（ＱＱ＝Ｑ１１＋Ｑ２２）。こ
の後、ステップ２３３で、各燃料噴射弁１４に、ステッ
プ２０２で算出した主燃料噴射量で主燃料噴射を実施す
るように噴射指令を出力する。As described above, the upstream catalyst temperature Taa
21 and the temperature zone to which the downstream catalyst temperature Tbb belongs, the basic HC supply amount Q11 is corrected to determine the HC supply amount as shown in FIG. The corrected HC supply amount Q22 is added to the supply amount Q11 to obtain H based on the active state (catalyst temperature) of both the upstream catalyst 19 and the downstream catalyst 20.
The C supply amount QQ is calculated (QQ = Q11 + Q22). Thereafter, in step 233, an injection command is output to each fuel injection valve 14 so as to execute the main fuel injection with the main fuel injection amount calculated in step 202.

【００８６】以上説明した本実施形態（３）の噴射制御
プログラムにより図２１に示すように補正ＨＣ供給量を
決定した場合の作用効果を説明する。The operation and effect when the corrected HC supply amount is determined as shown in FIG. 21 by the injection control program of the embodiment (3) described above will be described.

【００８７】（１）上流側触媒温度が第１の温度ゾーン
の場合 上流側触媒温度と下流側触媒温度が共に第１の温度ゾ
ーンの場合には、上流側触媒１９の活性状態が低いた
め、上流側触媒１９の活性状態が反映される基本ＨＣ供
給量Ｑ１１は少量又は０となる。増量補正により供給さ
れるＨＣの一部は上流側触媒１９に吸着され、残りのＨ
Ｃは上流側触媒１９を通過して下流側触媒２０に吸着さ
れる。吸着されたＨＣは、各触媒１９，２０がＮＯｘ浄
化下限温度Ｔ１以上に昇温したときに、離脱してＮＯｘ
浄化に用いられる。(1) When the upstream catalyst temperature is in the first temperature zone When both the upstream catalyst temperature and the downstream catalyst temperature are in the first temperature zone, the activation state of the upstream catalyst 19 is low. The basic HC supply amount Q11 reflecting the activation state of the upstream catalyst 19 is small or zero. Part of the HC supplied by the increase correction is adsorbed by the upstream catalyst 19, and the remaining H
C passes through the upstream catalyst 19 and is adsorbed by the downstream catalyst 20. The adsorbed HC is released and becomes NOx when each of the catalysts 19 and 20 rises to the NOx purification lower limit temperature T1 or higher.
Used for purification.

【００８８】上流側触媒温度が第１の温度ゾーンで、
下流側触媒温度が第２の温度ゾーンの場合には、上記
（１）のと同様に基本ＨＣ供給量Ｑ１１は少量又は０
となる。増量補正により供給されるＨＣの一部は上流側
触媒１９に吸着され、残りのＨＣは上流側触媒１９を通
過して下流側触媒２０でＮＯｘ浄化に用いられる。一
方、上流側触媒１９に吸着されたＨＣは、上流側触媒１
９がＮＯｘ浄化下限温度Ｔ１以上に昇温したときに、離
脱して上流側触媒１９又は下流側触媒２０でＮＯｘ浄化
に用いられる。更に、ＨＣの増量補正量を所定期間後又
は徐々に減量するため、上流側触媒１９のＨＣ被毒を防
止できると共に、燃費悪化を抑制でき、更に、上流側触
媒１９がＮＯｘ浄化下限温度Ｔ１以上に昇温したときの
ＮＯｘ浄化性能を向上できる。When the upstream catalyst temperature is in the first temperature zone,
When the downstream catalyst temperature is in the second temperature zone, the basic HC supply amount Q11 is small or zero as in (1) above.
Becomes Part of the HC supplied by the increase correction is adsorbed by the upstream catalyst 19, and the remaining HC passes through the upstream catalyst 19 and is used for NOx purification by the downstream catalyst 20. On the other hand, HC adsorbed by the upstream catalyst 19 is
When the temperature of the fuel cell 9 rises above the NOx purification lower limit temperature T1 or more, the fuel cell 9 is separated and used for NOx purification by the upstream catalyst 19 or the downstream catalyst 20. Further, since the increase correction amount of HC is reduced after a predetermined period or gradually, HC poisoning of the upstream side catalyst 19 can be prevented, fuel consumption can be prevented from deteriorating, and the upstream side catalyst 19 is not lower than the NOx purification lower limit temperature T1. NOx purification performance when the temperature is raised to a higher temperature.

【００８９】上流側触媒温度が第１の温度ゾーンで、
下流側触媒温度が第３の温度ゾーンの場合には、上記
（１）のと同様の作用効果が得られる。また、補正Ｈ
Ｃ供給量Ｑ２２は、下流側触媒温度がＮＯｘ浄化上限温
度Ｔ３近傍で少量となるので、比較的高温の下流側触媒
２０に供給されるＨＣ量を少なくして、下流側触媒２０
の過昇温を抑制することができる。When the upstream catalyst temperature is in the first temperature zone,
When the downstream catalyst temperature is in the third temperature zone, the same operation and effect as the above (1) can be obtained. The correction H
Since the downstream catalyst temperature is small near the NOx purification upper limit temperature T3, the amount of HC supplied to the downstream catalyst 20 having a relatively high temperature is reduced, and the C catalyst supply amount Q22 is reduced.
Overheating can be suppressed.

【００９０】上流側触媒温度が第１の温度ゾーンで、
下流側触媒温度が第４の温度ゾーンの場合には、ＨＣの
増量補正を行わないため、過昇温状態にある下流側触媒
２０の温度を早期にＮＯｘ浄化温度範囲内に戻すことが
できると共に、燃料消費も低減できる。When the upstream catalyst temperature is in the first temperature zone,
When the downstream catalyst temperature is in the fourth temperature zone, since the increase correction of HC is not performed, the temperature of the downstream catalyst 20 in the overheated state can be quickly returned to the NOx purification temperature range. In addition, fuel consumption can be reduced.

【００９１】（２）上流側触媒温度が第２の温度ゾーン
の場合 上流側触媒温度が第２の温度ゾーンで、下流側触媒温
度が第１の温度ゾーンの場合には、基本ＨＣ供給量Ｑ１
１に対してＨＣ増量補正することで、ＮＯｘ浄化温度範
囲内にある上流側触媒１９のＮＯｘ浄化率を向上しつ
つ、下流側触媒２０に供給するＨＣも増加する。下流側
触媒２０に到達したＨＣは、下流側触媒２０に吸着さ
れ、下流側触媒２０がＮＯｘ浄化下限温度Ｔ１以上に昇
温したときに、離脱してＮＯｘ浄化に用いられる。この
際、ＨＣの増量補正を所定期間のみにするため、下流側
触媒２０のＨＣ被毒を防止できると共に、燃費悪化を抑
制でき、更に、下流側触媒２０がＮＯｘ浄化下限温度Ｔ
１以上に昇温したときのＮＯｘ浄化性能を向上できる。(2) When the upstream catalyst temperature is in the second temperature zone When the upstream catalyst temperature is in the second temperature zone and the downstream catalyst temperature is in the first temperature zone, the basic HC supply amount Q1
By performing the HC increase correction to 1, the HC supplied to the downstream catalyst 20 increases while the NOx purification rate of the upstream catalyst 19 within the NOx purification temperature range is improved. The HC that has reached the downstream side catalyst 20 is adsorbed by the downstream side catalyst 20, and is separated and used for NOx purification when the temperature of the downstream side catalyst 20 rises to the NOx purification lower limit temperature T1 or more. At this time, since the increase correction of HC is performed only for a predetermined period, HC poisoning of the downstream side catalyst 20 can be prevented, deterioration of fuel efficiency can be suppressed, and the downstream side catalyst 20 has the NOx purification lower limit temperature T
The NOx purification performance when the temperature is increased to one or more can be improved.

【００９２】上流側触媒温度と下流側触媒温度が共に
第２の温度ゾーンの場合には、ＨＣ増量補正すること
で、上流側触媒１９のＮＯｘ浄化率を向上しつつ、下流
側触媒２０に供給するＨＣも増加する。下流側触媒２０
に到達したＨＣは、下流側触媒２０内に拡散し、上流側
触媒１９で浄化しきれなかったＮＯｘを浄化するため、
下流側触媒２０のＮＯｘ浄化率も向上する。この際、補
正ＨＣ供給量Ｑ２２は、下流側触媒温度がＮＯｘ浄化ピ
ーク温度Ｔ２近傍になるほど増加するので、下流側触媒
２０の活性状態が高くなるのに合わせて下流側触媒２０
へのＨＣ供給量を増やすことができ、下流側触媒２０の
ＮＯｘ浄化率を向上できる。When the upstream catalyst temperature and the downstream catalyst temperature are both in the second temperature zone, the increase in HC is corrected to improve the NOx purification rate of the upstream catalyst 19 and supply the same to the downstream catalyst 20. The amount of HC to be increased also increases. Downstream catalyst 20
Reaches the downstream catalyst 20 and purifies NOx that cannot be completely purified by the upstream catalyst 19.
The NOx purification rate of the downstream catalyst 20 is also improved. At this time, the corrected HC supply amount Q22 increases as the downstream catalyst temperature approaches the NOx purification peak temperature T2, and accordingly, the downstream catalyst 20 becomes higher as the activation state of the downstream catalyst 20 increases.
The amount of HC supplied to the catalyst can be increased, and the NOx purification rate of the downstream catalyst 20 can be improved.

【００９３】上流側触媒温度が第２の温度ゾーンで、
下流側触媒温度が第３の温度ゾーンの場合、上記（２）
のと同じように、上流側及び下流側触媒１９，２０の
ＮＯｘ浄化率を向上できる。また、補正ＨＣ供給量Ｑ２
２は、下流側触媒温度がＮＯｘ浄化上限温度Ｔ３近傍で
少量となるので、比較的高温の下流側触媒２０に供給す
るＨＣ量を少なくして、下流側触媒２０の過昇温を抑制
することができる。When the upstream catalyst temperature is in the second temperature zone,
When the downstream catalyst temperature is in the third temperature zone, the above (2)
Similarly to the above, the NOx purification rates of the upstream and downstream catalysts 19 and 20 can be improved. Further, the corrected HC supply amount Q2
2 is to reduce the amount of HC supplied to the relatively high-temperature downstream catalyst 20 to suppress the excessive temperature rise of the downstream catalyst 20 because the downstream catalyst temperature becomes small near the NOx purification upper limit temperature T3. Can be.

【００９４】上流側触媒温度が第２の温度ゾーンで、
下流側触媒温度が第４の温度ゾーンの場合には、ＨＣの
増量補正を行わないため、過昇温状態にある下流側触媒
２０の温度を早期にＮＯｘ浄化温度範囲内に戻すことが
できると共に、燃料消費も低減できる。When the upstream catalyst temperature is in the second temperature zone,
When the downstream catalyst temperature is in the fourth temperature zone, since the increase correction of HC is not performed, the temperature of the downstream catalyst 20 in the overheated state can be quickly returned to the NOx purification temperature range. In addition, fuel consumption can be reduced.

【００９５】（３）上流側触媒温度が第３の温度ゾーン
の場合 上流側触媒温度が第３の温度ゾーンで、下流側触媒温
度が第１の温度ゾーンの場合には、ＨＣ増量補正するこ
とで、上流側触媒１９のＮＯｘ浄化率を向上しつつ、下
流側触媒２０に供給されるＨＣも増加する。下流側触媒
２０に到達したＨＣは、下流側触媒２０に一旦、吸着さ
れるが、上流側触媒１９の比較的高温の流出ガスにより
下流側触媒２０が早期に昇温され、下流側触媒２０がＮ
Ｏｘ浄化下限温度Ｔ１以上に昇温したときに、離脱して
ＮＯｘ浄化に用いられる。(3) When the upstream catalyst temperature is in the third temperature zone When the upstream catalyst temperature is in the third temperature zone and the downstream catalyst temperature is in the first temperature zone, the HC increase correction is performed. Thus, the amount of HC supplied to the downstream catalyst 20 increases while improving the NOx purification rate of the upstream catalyst 19. The HC that has reached the downstream catalyst 20 is temporarily adsorbed by the downstream catalyst 20, but the temperature of the downstream catalyst 20 is quickly raised by the relatively high temperature effluent gas of the upstream catalyst 19, and the downstream catalyst 20 is discharged. N
When the temperature rises to the Ox purification lower limit temperature T1 or more, it is released and used for NOx purification.

【００９６】上流側触媒温度が第３の温度ゾーンで、
下流側触媒温度が第２の温度ゾーンの場合には、上記
（２）のと同じように、ＨＣ増量補正することで、上
流側触媒１９のＮＯｘ浄化率を向上しつつ、下流側触媒
２０に供給されるＨＣも増加して、下流側触媒２０のＮ
Ｏｘ浄化率も向上する。When the upstream catalyst temperature is in the third temperature zone,
When the downstream catalyst temperature is in the second temperature zone, the amount of HC is increased and the NOx purification rate of the upstream catalyst 19 is improved and the downstream catalyst 20 The supplied HC also increases, and the N
The Ox purification rate also improves.

【００９７】上流側触媒温度と下流側触媒温度が共に
第３の温度ゾーンの場合にも、上記（２）のと同じよ
うに、上流側及び下流側触媒１９，２０のＮＯｘ浄化率
を向上できる。Even when the upstream catalyst temperature and the downstream catalyst temperature are both in the third temperature zone, the NOx purification rates of the upstream and downstream catalysts 19 and 20 can be improved in the same manner as in the above (2). .

【００９８】ここで、上流側触媒温度が第３の温度ゾー
ンに属している場合、上流側触媒１９の流出ガス温度は
比較的高温である。従って、下流側触媒温度も第３の温
度ゾーンに属する場合に、ＨＣを供給し過ぎると、下流
側触媒２０が過昇温状態となりやすい。そこで、図２０
のステップ２２９では、補正ＨＣ供給量Ｑ２２を、ステ
ップ２２７で設定される補正ＨＣ供給量よりも小さく設
定する（又は０に設定しても良い）。これにより、下流
側触媒２０でのＨＣの反応を、下流側触媒温度が第２の
温度ゾーンの場合よりも少なくして、下流側触媒２０の
温度をＮＯｘ浄化温度範囲内（図２のＴ１〜Ｔ３）に維
持することができる。Here, when the upstream catalyst temperature belongs to the third temperature zone, the outflow gas temperature of the upstream catalyst 19 is relatively high. Therefore, if the downstream catalyst temperature also belongs to the third temperature zone and too much HC is supplied, the downstream catalyst 20 is likely to be in an excessively high temperature state. Therefore, FIG.
In step 229, the corrected HC supply amount Q22 is set smaller (or may be set to 0) than the corrected HC supply amount set in step 227. Thereby, the reaction of HC in the downstream side catalyst 20 is made lower than in the case where the downstream side catalyst temperature is in the second temperature zone, and the temperature of the downstream side catalyst 20 is set within the NOx purification temperature range (T1 to T1 in FIG. 2). T3).

【００９９】上流側触媒温度が第３の温度ゾーンで、
下流側触媒温度が第４の温度ゾーンの場合には、ＨＣの
増量補正を行わないため、過昇温状態にある下流側触媒
２０の触媒温度を早期にＮＯｘ浄化温度範囲内に戻すこ
とができると共に、燃料消費も低減できる。When the upstream catalyst temperature is in the third temperature zone,
When the downstream catalyst temperature is in the fourth temperature zone, the increase in HC is not corrected, so that the catalyst temperature of the downstream catalyst 20 in the overheated state can be quickly returned to the NOx purification temperature range. At the same time, fuel consumption can be reduced.

【０１００】（４）上流側触媒温度が第４の温度ゾーン
の場合 上流側触媒温度が第４の温度ゾーンに属している場合に
は、下流側触媒温度がいずれの温度ゾーンであっても、
ＨＣの増量補正を行わないため、過昇温状態にある上流
側触媒１９の温度を（下流側触媒温度が第４の温度ゾー
ンの場合には、下流側触媒２０の温度も）、早期にＮＯ
ｘ浄化温度範囲内に戻すことができると共に、燃料消費
も低減できる。(4) In the case where the upstream catalyst temperature is in the fourth temperature zone When the upstream catalyst temperature belongs to the fourth temperature zone, regardless of which temperature zone the downstream catalyst temperature belongs to,
Since the increase correction of HC is not performed, the temperature of the upstream side catalyst 19 in the overheated state (or the temperature of the downstream side catalyst 20 when the downstream side catalyst temperature is the fourth temperature zone) is set to NO at an early stage.
The temperature can be returned within the x purification temperature range, and the fuel consumption can be reduced.

【０１０１】以上説明した本実施形態（３）でも、前記
実施形態（１）と同じく、簡単な構成で、必要最小限の
ＨＣ供給量で排気ガス中のＮＯｘを浄化することがで
き、ＮＯｘ浄化率と燃費を向上させることができる（図
１５参照）。In the embodiment (3) described above, similarly to the embodiment (1), it is possible to purify NOx in exhaust gas with a simple structure and a necessary minimum amount of HC supply, and to purify NOx. The efficiency and fuel efficiency can be improved (see FIG. 15).

【０１０２】尚、上流側触媒温度の温度ゾーンと下流側
触媒温度の温度ゾーンとの各組み合わせによる補正ＨＣ
供給量Ｑ２２の設定値は、上記実施形態（３）に限定さ
れるものではなく、ＮＯｘ浄化率や燃費の向上を考慮に
入れて適宜変更しても良い。The correction HC by each combination of the temperature zone of the upstream catalyst temperature and the temperature zone of the downstream catalyst temperature.
The set value of the supply amount Q22 is not limited to the above-described embodiment (3), and may be appropriately changed in consideration of the improvement in the NOx purification rate and the fuel efficiency.

【０１０３】また、本実施形態（３）では、触媒温度に
応じて４つの温度ゾーンに区分したが、これよりも細か
く区分するようにしても良い。In the present embodiment (3), the temperature is divided into four temperature zones according to the catalyst temperature. However, the temperature zones may be divided more finely.

【０１０４】上記各実施形態（１）〜（３）では、上流
側触媒１９の下流に設けた排気温度センサ２１により上
流側触媒１９の流出ガス温度を検出することで、上流側
触媒１９の温度を判定するようにしたが、これ以外に、
上流側触媒１９の流入ガス温度と流出ガス温度を検出し
て両者から上流側触媒１９の温度を判定しても良い。そ
の際に、上流側触媒１９の流入ガス温度をエンジン運転
条件から算出しても良い。推定方法は、流入ガス温度と
流出ガス温度の加重平均値を用いる方法、流入ガス温
度、流出ガス温度、排気流量、触媒の熱伝達率及び触媒
の熱容量から熱量計算により求める方法等がある。In the above embodiments (1) to (3), the exhaust gas temperature of the upstream catalyst 19 is detected by the exhaust gas temperature sensor 21 provided downstream of the upstream catalyst 19, so that the temperature of the upstream catalyst 19 is reduced. Was determined, but in addition to this,
The temperature of the upstream catalyst 19 may be determined based on both the inflow gas temperature and the outflow gas temperature of the upstream catalyst 19. At this time, the inflow gas temperature of the upstream catalyst 19 may be calculated from the engine operating conditions. Examples of the estimation method include a method using a weighted average value of the inflow gas temperature and the outflow gas temperature, a method of calculating the calorific value from the inflow gas temperature, the outflow gas temperature, the exhaust flow rate, the heat transfer coefficient of the catalyst, and the heat capacity of the catalyst.

【０１０５】また、下流側触媒２０についても、上述の
ようにして、下流側触媒２０の流入ガス温度と流出ガス
温度を検出して両者から下流側触媒２０の温度を判定し
ても良い。この際、下流側触媒２０の流入ガス温度とし
て、上流側触媒１９の流出ガス温度を用いるようにして
も良い。As described above, the temperature of the downstream catalyst 20 may be determined by detecting the inflow gas temperature and the outflow gas temperature of the downstream catalyst 20 as described above. At this time, the outflow gas temperature of the upstream catalyst 19 may be used as the inflow gas temperature of the downstream catalyst 20.

【０１０６】更に、上記各実施形態（１）〜（３）で
は、ＮＯｘ触媒に還元剤（ＨＣ）を供給する炭化水素供
給手段として、燃料噴射弁１４の後噴射を用いたが、こ
れに代えて、上流側触媒１９の上流側の排気管１８に、
炭化水素供給手段としてインジェクタ等のＨＣ供給装置
を１つ取り付け、このＨＣ供給装置から排気管１８内に
ＨＣを供給するようにしても良い。Further, in each of the above embodiments (1) to (3), the post injection of the fuel injection valve 14 is used as the hydrocarbon supply means for supplying the reducing agent (HC) to the NOx catalyst. In the exhaust pipe 18 on the upstream side of the upstream catalyst 19,
One HC supply device such as an injector may be attached as the hydrocarbon supply means, and HC may be supplied into the exhaust pipe 18 from this HC supply device.

【０１０７】また、上記各実施形態（１）〜（３）で
は、排気管１８に２個の触媒１９，２０を直列に設けた
が、３個以上の触媒を直列に設けるようにしても良い。
この際、特許請求の範囲でいう「上流側触媒」と「下流
側触媒」は、例えば、３個の触媒を直列に設けた場合、
上流から順に１番目と２番目の触媒を上流側触媒、３
番目の触媒を下流側触媒としたり、最上流の触媒を上
流側触媒、２番目と３番目の触媒を下流側触媒とした
り、或は、最上流の触媒を上流側触媒、最下流の触媒
を下流側触媒としても良い。In the above embodiments (1) to (3), two catalysts 19 and 20 are provided in series in the exhaust pipe 18. However, three or more catalysts may be provided in series. .
At this time, “upstream catalyst” and “downstream catalyst” referred to in the claims are, for example, when three catalysts are provided in series,
The first and second catalysts in the order from the upstream are the upstream catalyst, 3
The third catalyst may be a downstream catalyst, the most upstream catalyst may be an upstream catalyst, the second and third catalysts may be downstream catalysts, or the most upstream catalyst may be an upstream catalyst, and the most downstream catalyst may be a downstream catalyst. A downstream catalyst may be used.

【図面の簡単な説明】[Brief description of the drawings]

【図１】本発明の実施形態（１）を示す排気浄化装置全
体の構成図FIG. 1 is an overall configuration diagram of an exhaust gas purification apparatus showing an embodiment (1) of the present invention.

【図２】触媒温度とＮＯｘ浄化率とＨＣ浄化率と温度ゾ
ーンとの関係を示す図FIG. 2 is a diagram showing a relationship among a catalyst temperature, a NOx purification rate, an HC purification rate, and a temperature zone.

【図３】実施形態（１）の噴射制御プログラムの処理の
流れを示すフローチャートFIG. 3 is a flowchart showing a flow of processing of an injection control program according to the embodiment (1).

【図４】（ａ）は上流側触媒温度とＮＯｘ排出量とから
基本ＨＣ供給量を求めるマップを概念的に示す図、
（ｂ）は下流側触媒温度とＮＯｘ排出量とから補正ＨＣ
供給量を求めるマップを概念的に示す図FIG. 4A is a diagram conceptually showing a map for obtaining a basic HC supply amount from an upstream catalyst temperature and a NOx emission amount,
(B) shows the corrected HC based on the downstream catalyst temperature and the NOx emission amount.
Diagram showing conceptually map for obtaining supply amount

【図５】上流側及び下流側触媒の温度分布を示す図（そ
の１）FIG. 5 is a diagram showing a temperature distribution of an upstream side catalyst and a downstream side catalyst (part 1).

【図６】（ａ）は上流側触媒温度Ｔａから基本ＨＣ供給
量Ｑ１ａを求める方法を説明する図、（ｂ）は下流側触
媒温度Ｔｂから補正ＨＣ供給量Ｑ２ｂを求める方法を説
明する図6A is a diagram illustrating a method of calculating a basic HC supply amount Q1a from an upstream catalyst temperature Ta, and FIG. 6B is a diagram illustrating a method of calculating a corrected HC supply amount Q2b from a downstream catalyst temperature Tb.

【図７】上流側及び下流側触媒の温度分布を示す図（そ
の２）FIG. 7 is a diagram showing a temperature distribution of an upstream side catalyst and a downstream side catalyst (part 2).

【図８】（ａ）と（ｂ）は、Ｑ１max ＞Ｑ２max と設定
した場合の基本ＨＣ供給量と補正ＨＣ供給量のマップを
概念的に示す図FIGS. 8A and 8B are diagrams conceptually showing maps of a basic HC supply amount and a corrected HC supply amount when Q1max> Q2max is set.

【図９】（ａ）と（ｂ）は、Ｑ１max ＜Ｑ２max と設定
した場合の基本ＨＣ供給量と補正ＨＣ供給量のマップを
概念的に示す図FIGS. 9A and 9B are diagrams conceptually showing maps of a basic HC supply amount and a corrected HC supply amount when Q1max <Q2max is set.

【図１０】Ｑ１max ＞Ｑ２max と設定した場合と、Ｑ１
max ＜Ｑ２max と設定した場合のＨＣ供給量を比較した
図FIG. 10 shows a case where Q1max> Q2max is set, and a case where Q1max is set.
Diagram comparing HC supply amounts when max <Q2max is set

【図１１】上流側及び下流側触媒の温度分布を示す図
（その３）FIG. 11 is a diagram showing a temperature distribution of an upstream side catalyst and a downstream side catalyst (part 3).

【図１２】（ａ）は上流側触媒温度Ｔｇから基本ＨＣ供
給量Ｑ１ｇを求める方法を説明する図、（ｂ）は下流側
触媒温度Ｔｈから補正ＨＣ供給量Ｑ２ｈを求める方法を
説明する図12A is a diagram illustrating a method of calculating a basic HC supply amount Q1g from an upstream catalyst temperature Tg, and FIG. 12B is a diagram illustrating a method of calculating a corrected HC supply amount Q2h from a downstream catalyst temperature Th.

【図１３】（ａ）はＱmax を設定した場合の上流側及び
下流側触媒の温度分布を示す図、（ｂ）はＱmax を設定
しない場合の上流側及び下流側触媒の温度分布を示す図13A is a diagram showing the temperature distribution of the upstream and downstream catalysts when Qmax is set, and FIG. 13B is a diagram showing the temperature distribution of the upstream and downstream catalysts when Qmax is not set.

【図１４】Ｑmax を設定した場合と、Ｑmax を設定しな
い場合のＨＣ供給量を比較した図FIG. 14 is a diagram comparing HC supply amounts when Qmax is set and when Qmax is not set.

【図１５】実施形態（１）〜（３）と比較例について、
燃費悪化とＮＯｘ浄化率とを測定した結果を示す図FIG. 15 shows Embodiments (1) to (3) and a comparative example.
The figure which shows the result of having measured fuel consumption deterioration and NOx purification rate.

【図１６】実施形態（１）と比較例について、流入ガス
温度に対する触媒中心温度の挙動を比較したタイムチャ
ートFIG. 16 is a time chart comparing the behavior of the catalyst center temperature with respect to the inflow gas temperature for the embodiment (1) and the comparative example.

【図１７】実施形態（２）における下流側触媒温度と補
正ＨＣ供給量との関係を示す図FIG. 17 is a diagram showing the relationship between the downstream catalyst temperature and the corrected HC supply amount in the embodiment (2).

【図１８】上流側触媒温度と上限ＨＣ供給量Ｑmax との
関係を示す図FIG. 18 is a diagram showing a relationship between an upstream catalyst temperature and an upper limit HC supply amount Qmax.

【図１９】実施形態（２）の噴射制御プログラムの処理
の流れを示すフローチャートFIG. 19 is a flowchart showing the flow of processing of an injection control program according to the embodiment (2).

【図２０】図１９の続きのフローチャートFIG. 20 is a flowchart continued from FIG. 19;

【図２１】上流側触媒温度の温度ゾーンと下流側触媒温
度の温度ゾーンとの各組み合わせと補正ＨＣ供給量Ｑ２
２との関係を示す図FIG. 21 shows each combination of a temperature zone of an upstream catalyst temperature and a temperature zone of a downstream catalyst temperature, and a corrected HC supply amount Q2.
Diagram showing the relationship with 2.

【符号の説明】[Explanation of symbols]

１０…ディーゼルエンジン（内燃機関）、１１…吸気
管、１４…燃料噴射弁（炭化水素供給手段）、１５…燃
料ポンプ、１８…排気管（排気通路）、１９…上流側触
媒、２０…下流側触媒、２１…排気温度センサ（上流側
触媒温度判定手段）、２２…排気温度センサ（下流側触
媒温度判定手段）、２３…ＥＣＵ（基本供給量決定手
段，補正供給量決定手段，炭化水素供給量決定手段，窒
素酸化物排出量算出手段）。Reference Signs List 10: diesel engine (internal combustion engine), 11: intake pipe, 14: fuel injection valve (hydrocarbon supply means), 15: fuel pump, 18: exhaust pipe (exhaust passage), 19: upstream catalyst, 20: downstream Catalyst, 21: exhaust temperature sensor (upstream catalyst temperature determining means), 22: exhaust temperature sensor (downstream catalyst temperature determining means), 23: ECU (basic supply amount determining means, correction supply amount determining means, hydrocarbon supply amount) Determination means, nitrogen oxide emission amount calculation means).

───────────────────────────────────────────────────── フロントページの続き (72)発明者 小島 大輔 愛知県刈谷市昭和町１丁目１番地 株式会 社デンソー内 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Daisuke Kojima 1-1-1, Showa-cho, Kariya-shi, Aichi Prefecture Inside DENSO Corporation

Claims (13)

【特許請求の範囲】[Claims] 【請求項１】 内燃機関の排気通路に排気中の窒素酸化
物を浄化する複数の触媒を直列に配設した内燃機関の排
気浄化装置において、 前記複数の触媒のうちの上流側の触媒（以下「上流側触
媒」という）の温度を判定する上流側触媒温度判定手段
と、 前記複数の触媒のうちの下流側の触媒（以下「下流側触
媒」という）の温度を判定する下流側触媒温度判定手段
と、 前記複数の触媒の上流から各触媒に窒素酸化物の還元剤
として炭化水素を供給する炭化水素供給手段と、 少なくとも前記上流側触媒の判定温度と前記内燃機関の
運転状態とに基づいて基本炭化水素供給量を決定する基
本供給量決定手段と、 少なくとも前記下流側触媒の判定温度と前記内燃機関の
運転状態とに基づいて補正炭化水素供給量を決定する補
正供給量決定手段と、 前記基本炭化水素供給量を前記補正炭化水素供給量で補
正して前記炭化水素供給手段による炭化水素供給量を決
定する炭化水素供給量決定手段とを備えていることを特
徴とする内燃機関の排気浄化装置。1. An exhaust purification system for an internal combustion engine in which a plurality of catalysts for purifying nitrogen oxides in exhaust gas are arranged in series in an exhaust passage of the internal combustion engine. Upstream catalyst temperature determination means for determining the temperature of an "upstream catalyst"; and downstream catalyst temperature determination for determining the temperature of a downstream catalyst (hereinafter referred to as "downstream catalyst") of the plurality of catalysts. Means, a hydrocarbon supply means for supplying a hydrocarbon as a reducing agent for nitrogen oxides to each catalyst from upstream of the plurality of catalysts, and at least a determination temperature of the upstream catalyst and an operating state of the internal combustion engine. Basic supply amount determining means for determining a basic hydrocarbon supply amount; corrected supply amount determining means for determining a corrected hydrocarbon supply amount based on at least a determination temperature of the downstream catalyst and an operating state of the internal combustion engine; A hydrocarbon supply amount determining means for correcting the basic hydrocarbon supply amount with the corrected hydrocarbon supply amount to determine the hydrocarbon supply amount by the hydrocarbon supply means. Purification device. 【請求項２】 前記基本炭化水素供給量の最大値は、前
記補正炭化水素供給量の最大値よりも大きく設定されて
いることを特徴とする請求項１に記載の内燃機関の排気
浄化装置。2. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the maximum value of the basic hydrocarbon supply amount is set to be larger than the maximum value of the corrected hydrocarbon supply amount. 【請求項３】 前記炭化水素供給量決定手段は、前記炭
化水素供給量の上限値（以下「上限炭化水素供給量」と
いう）を前記基本炭化水素供給量の最大値と同一又はそ
れ以下に設定することを特徴とする請求項１又は２に記
載の内燃機関の排気浄化装置。3. The hydrocarbon supply amount determining means sets an upper limit value of the hydrocarbon supply amount (hereinafter, referred to as an “upper limit hydrocarbon supply amount”) to be equal to or less than the maximum value of the basic hydrocarbon supply amount. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1 or 2, wherein: 【請求項４】 前記炭化水素供給量決定手段は、前記上
限炭化水素供給量を前記上流側触媒の判定温度に応じて
設定することを特徴とする請求項３に記載の内燃機関の
排気浄化装置。4. The exhaust gas purifying apparatus for an internal combustion engine according to claim 3, wherein the hydrocarbon supply amount determining means sets the upper limit hydrocarbon supply amount according to a determination temperature of the upstream catalyst. . 【請求項５】 前記基本炭化水素供給量又は前記補正炭
化水素供給量の触媒温度に対する増減特性は、窒素酸化
物浄化率が最大になる浄化ピーク温度以上の領域での触
媒温度上昇による減少割合が、浄化ピーク温度以下の領
域での触媒温度上昇による増加割合よりも大きくなるよ
うに設定されていることを特徴とする請求項１乃至４の
いずれかに記載の内燃機関の排気浄化装置。5. The increase / decrease characteristic of the basic hydrocarbon supply amount or the correction hydrocarbon supply amount with respect to the catalyst temperature is such that a decrease rate due to a catalyst temperature rise in a region equal to or higher than a purification peak temperature at which the nitrogen oxide purification ratio is maximized is determined. The exhaust gas purifying apparatus for an internal combustion engine according to any one of claims 1 to 4, wherein the rate of increase is set to be greater than an increase rate due to a rise in catalyst temperature in a region equal to or lower than a purification peak temperature. 【請求項６】 内燃機関の排気通路に排気中の窒素酸化
物を浄化する複数の触媒を直列に配設した内燃機関の排
気浄化装置において、 前記複数の触媒のうちの上流側の触媒（以下「上流側触
媒」という）の温度を判定する上流側触媒温度判定手段
と、 前記複数の触媒のうちの下流側の触媒（以下「下流側触
媒」という）の温度を判定する下流側触媒温度判定手段
と、 前記複数の触媒の上流から各触媒に窒素酸化物の還元剤
として炭化水素を供給する炭化水素供給手段と、 少なくとも前記上流側触媒の判定温度と前記内燃機関の
運転状態とに基づいて基本炭化水素供給量を決定する基
本供給量決定手段と、 前記上流側触媒と前記下流側触媒の窒素酸化物浄化率に
応じて複数の温度ゾーンに区分し、前記上流側触媒の判
定温度が属する温度ゾーンと前記下流側触媒の判定温度
が属する温度ゾーンとの組み合わせにより前記基本炭化
水素供給量を補正して前記炭化水素供給手段による炭化
水素供給量を決定する炭化水素供給量決定手段とを備え
ていることをことを特徴とする内燃機関の排気浄化装
置。6. An exhaust gas purification apparatus for an internal combustion engine in which a plurality of catalysts for purifying nitrogen oxides in exhaust gas are disposed in series in an exhaust passage of the internal combustion engine, wherein an upstream catalyst (hereinafter referred to as a catalyst) of the plurality of catalysts is provided. Upstream catalyst temperature determination means for determining the temperature of an "upstream catalyst"; and downstream catalyst temperature determination for determining the temperature of a downstream catalyst (hereinafter referred to as "downstream catalyst") of the plurality of catalysts. Means, a hydrocarbon supply means for supplying a hydrocarbon as a reducing agent of nitrogen oxide to each catalyst from upstream of the plurality of catalysts, based on at least a determination temperature of the upstream catalyst and an operating state of the internal combustion engine. A basic supply amount determining means for determining a basic hydrocarbon supply amount; dividing into a plurality of temperature zones according to a nitrogen oxide purification rate of the upstream catalyst and the downstream catalyst, to which a determination temperature of the upstream catalyst belongs Temperature zo And a temperature zone to which the determination temperature of the downstream catalyst belongs, and a hydrocarbon supply amount determining means for correcting the basic hydrocarbon supply amount to determine the hydrocarbon supply amount by the hydrocarbon supply means. An exhaust gas purifying apparatus for an internal combustion engine, comprising: 【請求項７】 前記複数の温度ゾーンは、窒素酸化物浄
化率が低いレベルで推移する低温の第１の温度ゾーン
と、窒素酸化物浄化率が温度と共に上昇する第２の温度
ゾーンと、窒素酸化物浄化率が温度と共に低下する第３
の温度ゾーンと、窒素酸化物浄化率が低いレベルで推移
する高温の第４の温度ゾーンとに区分されていることを
特徴とする請求項６に記載の内燃機関の排気浄化装置。7. The plurality of temperature zones include a first temperature zone at a low temperature where the nitrogen oxide purification rate changes at a low level, a second temperature zone where the nitrogen oxide purification rate increases with temperature, and nitrogen. Oxide purification rate decreases with temperature
7. The exhaust gas purifying apparatus for an internal combustion engine according to claim 6, wherein the temperature zone is divided into a temperature zone having a low temperature and a fourth temperature zone having a high temperature at which the nitrogen oxide purification rate changes at a low level. 【請求項８】 前記炭化水素供給量決定手段は、前記上
流側触媒の判定温度が前記第２又は第３の温度ゾーンに
属し且つ前記下流側触媒の判定温度が前記第１乃至第３
の温度ゾーンのいずれかに属しているときに、前記基本
炭化水素供給量を増量補正することを特徴とする請求項
７に記載の内燃機関の排気浄化装置。8. The hydrocarbon supply amount determining means, wherein the determination temperature of the upstream catalyst belongs to the second or third temperature zone, and the determination temperature of the downstream catalyst is the first to third temperature zones.
The exhaust gas purification apparatus for an internal combustion engine according to claim 7, wherein the basic hydrocarbon supply amount is increased and corrected when it belongs to any one of the temperature zones. 【請求項９】 前記炭化水素供給量決定手段は、前記下
流側触媒の判定温度が前記第１の温度ゾーンに属してい
るときに、前記基本炭化水素供給量を所定期間のみ増量
補正することを特徴とする請求項８に記載の内燃機関の
排気浄化装置。9. The method according to claim 9, wherein the hydrocarbon supply amount determination means increases and corrects the basic hydrocarbon supply amount only for a predetermined period when the determination temperature of the downstream catalyst belongs to the first temperature zone. The exhaust gas purifying apparatus for an internal combustion engine according to claim 8, wherein: 【請求項１０】 前記炭化水素供給量決定手段は、前記
下流側触媒の判定温度が前記第３の温度ゾーンに属して
いる場合の前記基本炭化水素供給量に対する増量補正量
を前記下流側触媒の判定温度が前記第２の温度ゾーンに
属している場合よりも小さく設定することを特徴とする
請求項７乃至９のいずれかに記載の内燃機関の排気浄化
装置。10. The hydrocarbon supply amount determining means determines an increase correction amount for the basic hydrocarbon supply amount when the determination temperature of the downstream catalyst belongs to the third temperature zone. The exhaust gas purifying apparatus for an internal combustion engine according to any one of claims 7 to 9, wherein the determination temperature is set to be lower than when the temperature belongs to the second temperature zone. 【請求項１１】 前記炭化水素供給量決定手段は、前記
上流側触媒の判定温度が前記第１の温度ゾーンに属し且
つ前記下流側触媒の判定温度が前記第２又は第３の温度
ゾーンに属しているときに、前記基本炭化水素供給量を
増量補正することを特徴とする請求項７乃至１０のいず
れかに記載の内燃機関の排気浄化装置。11. The hydrocarbon supply amount determination means, wherein the determination temperature of the upstream catalyst belongs to the first temperature zone and the determination temperature of the downstream catalyst belongs to the second or third temperature zone. The exhaust gas purifying apparatus for an internal combustion engine according to any one of claims 7 to 10, wherein the correction amount of the basic hydrocarbon supply amount is increased during the operation. 【請求項１２】 前記炭化水素供給量決定手段は、前記
基本炭化水素供給量に対する増量補正量を時間の経過と
共に減少させることを特徴とする請求項１１に記載の内
燃機関の排気浄化装置。12. The exhaust gas purifying apparatus for an internal combustion engine according to claim 11, wherein said hydrocarbon supply amount determining means decreases an increase correction amount with respect to said basic hydrocarbon supply amount over time. 【請求項１３】 内燃機関の排気通路に排気中の窒素酸
化物を浄化する複数の触媒を直列に配設した内燃機関の
排気浄化装置において、 前記複数の触媒のうちの上流側の触媒（以下「上流側触
媒」という）の温度を判定する上流側触媒温度判定手段
と、 前記複数の触媒のうちの下流側の触媒（以下「下流側触
媒」という）の温度を判定する下流側触媒温度判定手段
と、 前記複数の触媒の上流から各触媒に窒素酸化物の還元剤
として炭化水素を供給する炭化水素供給手段と、 前記内燃機関の運転状態から窒素酸化物の排出量を算出
する窒素酸化物排出量算出手段と、 前記上流側触媒の判定温度、前記下流側触媒の判定温度
及び前記窒素酸化物排出量に基づいて前記炭化水素供給
手段による炭化水素供給量を決定する炭化水素供給量決
定手段とを備えていることを特徴とする内燃機関の排気
浄化装置。13. An exhaust gas purification apparatus for an internal combustion engine, wherein a plurality of catalysts for purifying nitrogen oxides in exhaust gas are arranged in series in an exhaust passage of the internal combustion engine. Upstream catalyst temperature determination means for determining the temperature of an "upstream catalyst"; and downstream catalyst temperature determination for determining the temperature of a downstream catalyst (hereinafter referred to as "downstream catalyst") of the plurality of catalysts. Means, a hydrocarbon supply means for supplying a hydrocarbon as a reducing agent of nitrogen oxide to each catalyst from upstream of the plurality of catalysts, and a nitrogen oxide for calculating a nitrogen oxide emission amount from an operation state of the internal combustion engine Emission amount calculation means, and a hydrocarbon supply amount determination means for determining a hydrocarbon supply amount by the hydrocarbon supply means based on the determination temperature of the upstream catalyst, the determination temperature of the downstream catalyst, and the nitrogen oxide emission amount. When Exhaust purification system of an internal combustion engine, characterized in that it comprises.