JP2011231718A - Exhaust emission control device of internal combustion engine - Google Patents

Exhaust emission control device of internal combustion engine Download PDF

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JP2011231718A
JP2011231718A JP2010103896A JP2010103896A JP2011231718A JP 2011231718 A JP2011231718 A JP 2011231718A JP 2010103896 A JP2010103896 A JP 2010103896A JP 2010103896 A JP2010103896 A JP 2010103896A JP 2011231718 A JP2011231718 A JP 2011231718A
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temperature
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Akira Kenjo
晃 見上
Shinya Hirota
信也 広田
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Toyota Motor Corp
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Abstract

PROBLEM TO BE SOLVED: To prevent deterioration in fuel consumption due to temperature increase control of an exhaust emission control catalyst in an internal combustion engine.SOLUTION: An exhaust emission control device includes: an oxidation catalyst and a downstream-side exhaust emission control catalyst; a unit for controlling temperature increase of the oxidation catalyst and the exhaust emission control catalyst; a unit for detecting temperature distribution of the flowing direction of exhaust emission of the oxidation catalyst; a temperature increase strength adjusting unit for adjusting a strength of catalyst temperature increase control; and a temperature increase strength adjusting unit for adjusting the strength of the catalyst temperature increase control to a predetermined value when the temperature of the exhaust emission control catalyst is lower than a predetermined active temperature, and adjusting the strength of the catalyst temperature increase control to a level lower than the predetermined strength when the temperature of the exhaust emission control catalyst increases higher than the active temperature by the predetermined strength of the catalyst temperature increase control, and the temperature of the exhaust emission control catalyst is higher than the active temperature and at least a temperature at a predetermined area in the neighborhood of the downstream end of the oxidation catalyst is higher than the active temperature of the oxidation catalyst in a temperature distribution detected by the temperature distribution detector.

Description

本発明は、内燃機関の排気浄化装置に関する。   The present invention relates to an exhaust emission control device for an internal combustion engine.

内燃機関の排気通路に設けられた排気浄化触媒を早期昇温する技術が開発されている。例えば、排気中のＮＯｘを浄化するＮＯｘ浄化触媒を機関始動時に早期昇温する技術として、ＮＯｘ浄化触媒の上流に配置した酸化触媒に未燃燃料（ＨＣ）を添加し、酸化触媒においてＨＣが酸化反応することで発生する熱でＮＯｘ浄化触媒上流の排気の温度を上昇させることにより、ＮＯｘ浄化触媒を昇温する技術が記載されている。   A technique for quickly raising the temperature of an exhaust purification catalyst provided in an exhaust passage of an internal combustion engine has been developed. For example, as a technique for quickly raising the temperature of a NOx purification catalyst that purifies NOx in exhaust gas when the engine is started, unburned fuel (HC) is added to an oxidation catalyst arranged upstream of the NOx purification catalyst, and HC is oxidized in the oxidation catalyst. A technique is described in which the temperature of the NOx purification catalyst is raised by increasing the temperature of the exhaust gas upstream of the NOx purification catalyst with the heat generated by the reaction.

このようなＮＯｘ浄化触媒の昇温技術に関して、酸化触媒をすり抜けたＨＣがＮＯｘ浄化触媒に吸着してＮＯｘ浄化触媒が被毒することがある。これに対し、ＮＯｘ浄化触媒の上流に大量のＨＣを添加することによってＮＯｘ浄化触媒を活性温度（約３５０℃）より高いＨＣ離脱温度（約６００℃）まで昇温させることによりＮＯｘ浄化触媒のＨＣ被毒を抑制する技術が提案されている（特許文献１を参照）。   With regard to such a temperature raising technique for the NOx purification catalyst, HC that has passed through the oxidation catalyst may be adsorbed to the NOx purification catalyst and poison the NOx purification catalyst. On the other hand, by adding a large amount of HC upstream of the NOx purification catalyst, the NOx purification catalyst is heated to an HC desorption temperature (about 600 ° C.) higher than the activation temperature (about 350 ° C.) to thereby increase the HC of the NOx purification catalyst. A technique for suppressing poisoning has been proposed (see Patent Document 1).

特開２００８−２３１９６６号公報JP 2008-231966 A 特開２０００−１８６５４１号公報JP 2000-186541 A

従来、酸化触媒、パティキュレートフィルタ、及びＮＯｘ浄化触媒などの排気浄化触媒を排気通路に直列に配置した構成の排気浄化装置において、最下流側の排気浄化触媒の温度を活性温度まで昇温させるために、上流側にある酸化触媒やフィルタをそれより高い温度まで昇温する昇温制御が行われている。   2. Description of the Related Art Conventionally, in an exhaust purification device having a configuration in which exhaust purification catalysts such as an oxidation catalyst, a particulate filter, and a NOx purification catalyst are arranged in series in an exhaust passage, the temperature of the exhaust purification catalyst on the most downstream side is raised to the activation temperature. In addition, temperature rise control is performed to raise the temperature of the upstream oxidation catalyst and filter to a higher temperature.

なお、排気浄化触媒が活性化した状態とは、排気浄化触媒が排気中の所定の成分（ＮＯｘ浄化触媒の場合はＮＯｘ）に対して所望の浄化能力を発揮することが可能な状態を意味するものとする。逆に、排気浄化触媒が非活性の状態とは、排気浄化触媒が排気中の所定の成分に対して所望の浄化能力を発揮することができない状態を意味するものとする。   The state in which the exhaust purification catalyst is activated means a state in which the exhaust purification catalyst can exhibit a desired purification capability with respect to a predetermined component in exhaust (NOx in the case of a NOx purification catalyst). Shall. Conversely, the state in which the exhaust purification catalyst is inactive means a state in which the exhaust purification catalyst cannot exhibit a desired purification capability for a predetermined component in the exhaust.

例えば、アンモニアを還元剤として排気中のＮＯｘを選択的に還元浄化する選択還元型ＮＯｘ触媒の場合、触媒温度が或る活性下限温度より低い状態では、十分な触媒活性が得られないために所望のＮＯｘ浄化率を得ることができない。また、触媒温度が或る活性上限温度より高い状態では、触媒活性は得られるもののアンモニアが触媒に吸着しにくくなるために所望のＮＯｘ浄化率を得ることができない。   For example, in the case of a selective reduction type NOx catalyst that selectively reduces and purifies NOx in exhaust using ammonia as a reducing agent, sufficient catalytic activity cannot be obtained in a state where the catalyst temperature is lower than a certain activity lower limit temperature. NOx purification rate cannot be obtained. Further, in a state where the catalyst temperature is higher than a certain activity upper limit temperature, although catalyst activity is obtained, ammonia becomes difficult to adsorb on the catalyst, so that a desired NOx purification rate cannot be obtained.

このように触媒温度が活性上限温度より高いために所望のＮＯｘ浄化率を得ることができない状態も、選択還元型ＮＯｘ触媒が非活性である状態に含ませるものとする。選択還元型ＮＯｘ触媒の場合は、上述した活性下限温度から活性上限温度までの温度範囲が、選択還元型ＮＯｘ触媒が活性化する温度範囲（所望のＮＯｘ浄化率が得られる温度範囲）となる。   The state where the desired NOx purification rate cannot be obtained because the catalyst temperature is higher than the activation upper limit temperature is also included in the state where the selective reduction type NOx catalyst is inactive. In the case of a selective reduction type NOx catalyst, the temperature range from the above-mentioned lower limit of activation temperature to the upper limit of activation temperature is a temperature range in which the selective reduction type NOx catalyst is activated (a temperature range in which a desired NOx purification rate can be obtained).

このような昇温制御では、排気浄化触媒を昇温させる場合に、排気浄化触媒より上流側にある酸化触媒やパティキュレートフィルタも活性温度以上の高温に昇温することになり
、過剰な昇温制御によって燃費性能が低下する可能性があった。 In such temperature raising control, when raising the temperature of the exhaust purification catalyst, the oxidation catalyst and the particulate filter upstream of the exhaust purification catalyst are also raised to a temperature higher than the activation temperature. There is a possibility that the fuel efficiency will be reduced by the control.

本発明はこの点に鑑みてなされたものであり、排気通路に配置される排気浄化触媒を昇温させる制御において燃費の悪化を抑制す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を目的とする。   The present invention has been made in view of this point, and an object of the present invention is to provide an exhaust purification device for an internal combustion engine that can suppress deterioration of fuel consumption in control for raising the temperature of an exhaust purification catalyst disposed in an exhaust passage. And

上記の課題を解決するための本発明は、
内燃機関の排気通路に設けられる酸化触媒と、
前記酸化触媒より下流側の排気通路に設けられる排気浄化触媒と、
前記酸化触媒及び前記排気浄化触媒の温度を上昇させる触媒昇温制御を実行する触媒昇温手段と、
前記酸化触媒の排気の流れ方向の温度分布を検出する温度分布検出手段と、
前記触媒昇温手段による触媒昇温制御の強度を調節する昇温強度調節手段と、
前記排気浄化触媒の温度が所定の活性温度より低い場合は、前記触媒昇温制御の強度を所定の強度に調節し、該所定の強度の触媒昇温制御により前記排気浄化触媒の温度が活性温度以上に上昇した場合は、前記排気浄化触媒の温度が活性温度以上かつ前記温度分布検出手段により検出される温度分布において少なくとも前記酸化触媒の下流端近傍の所定領域の温度が酸化触媒の活性温度以上であれば、前記触媒昇温制御の強度を前記所定の強度よりも弱い強度に調節するように、前記昇温強度調節手段を制御する制御手段と、
を備える内燃機関の排気浄化装置である。 The present invention for solving the above problems is as follows.
An oxidation catalyst provided in the exhaust passage of the internal combustion engine;
An exhaust purification catalyst provided in an exhaust passage downstream of the oxidation catalyst;
Catalyst temperature raising means for performing catalyst temperature raising control for raising the temperature of the oxidation catalyst and the exhaust purification catalyst;
Temperature distribution detecting means for detecting a temperature distribution in the exhaust flow direction of the oxidation catalyst;
A temperature increase intensity adjusting means for adjusting the intensity of the catalyst temperature increase control by the catalyst temperature increase means;
When the temperature of the exhaust purification catalyst is lower than a predetermined activation temperature, the intensity of the catalyst temperature increase control is adjusted to a predetermined intensity, and the temperature of the exhaust purification catalyst is increased to the activation temperature by the catalyst temperature increase control with the predetermined intensity. When the temperature rises above, the temperature of the exhaust purification catalyst is equal to or higher than the activation temperature, and at least the temperature in the predetermined region near the downstream end of the oxidation catalyst is equal to or higher than the activation temperature of the oxidation catalyst in the temperature distribution detected by the temperature distribution detection means. If so, control means for controlling the temperature rise intensity adjusting means so as to adjust the intensity of the catalyst temperature rise control to a weaker intensity than the predetermined intensity,
An exhaust emission control device for an internal combustion engine.

このような酸化触媒及び排気浄化触媒が直列配置された排気浄化装置では、排気浄化触媒を活性温度以上に昇温させるために、酸化触媒も活性温度或いはそれよりも更に高い温度まで昇温していた。しかしながら、酸化触媒は過剰に昇温されていることになり、燃費性能が低下する原因ともなっていた。   In such an exhaust purification device in which an oxidation catalyst and an exhaust purification catalyst are arranged in series, in order to raise the temperature of the exhaust purification catalyst above the activation temperature, the oxidation catalyst is also raised to the activation temperature or a temperature higher than that. It was. However, the temperature of the oxidation catalyst has been excessively increased, which has been a cause of a reduction in fuel consumption performance.

この点、本発明においては、所定の強度の触媒昇温制御により酸化触媒及び排気浄化触媒の昇温を行って排気浄化触媒の温度が活性温度以上に上昇した場合には、排気浄化触媒の温度が活性温度以上かつ酸化触媒の下流端近傍の所定領域が活性化しているという条件が満足される限りにおいて、触媒昇温制御の強度が弱められる。これにより、触媒昇温制御に係るエネルギー消費が抑えられるので、燃費性能の低下を抑制できる。   In this regard, in the present invention, when the temperature of the oxidation catalyst and the exhaust purification catalyst is raised by the catalyst temperature increase control with a predetermined strength and the temperature of the exhaust purification catalyst rises above the activation temperature, the temperature of the exhaust purification catalyst As long as the condition that the predetermined region near the downstream end of the oxidation catalyst is activated is satisfied, the strength of the catalyst temperature increase control is weakened. Thereby, since the energy consumption concerning catalyst temperature rising control is suppressed, the fall of a fuel consumption performance can be suppressed.

触媒昇温制御の強度が弱められると、酸化触媒の温度は低下する。しかしながら、酸化触媒の温度は上流側から徐々に低下していくので、触媒昇温制御の強度が弱められてからしばらくの間は、上流側の領域が酸化触媒の活性温度より低く非活性であるものの下流側の領域は活性温度以上で活性化しているという状態になる。   When the intensity of the catalyst temperature increase control is weakened, the temperature of the oxidation catalyst decreases. However, since the temperature of the oxidation catalyst gradually decreases from the upstream side, the upstream region is lower than the activation temperature of the oxidation catalyst and is inactive for a while after the strength of the catalyst temperature increase control is weakened. The region on the downstream side of the object is activated at an activation temperature or higher.

本発明では、このように酸化触媒の一部領域が非活性状態になることを許容する。すなわち、「酸化触媒の少なくとも下流端近傍の所定領域が活性化している状態」には、酸化触媒の上流側の領域が活性化していない状態（温度が酸化触媒の活性温度より低い状態）が含まれる。   In the present invention, a partial region of the oxidation catalyst is allowed to become inactive in this way. That is, “a state where at least a predetermined region near the downstream end of the oxidation catalyst is activated” includes a state where the region upstream of the oxidation catalyst is not activated (a state where the temperature is lower than the activation temperature of the oxidation catalyst). It is.

本発明によれば、排気浄化触媒が活性状態であることを条件に、酸化触媒の一部領域が非活性状態となることを許容して、触媒昇温制御を弱めるので、触媒昇温制御に係るエネルギー消費を抑えることが可能になる。   According to the present invention, on the condition that the exhaust purification catalyst is in an active state, a partial region of the oxidation catalyst is allowed to become inactive, and the catalyst temperature increase control is weakened. Such energy consumption can be suppressed.

なお、酸化触媒の全域が非活性状態となった場合や酸化触媒の下流端近傍の所定領域が非活性状態となった場合には、触媒昇温制御の強度を元に戻す（酸化触媒及び排気浄化触媒を活性温度より低い状態から活性温度以上の状態へ昇温する際の触媒昇温制御の強度に
する）ことができる。また、排気浄化触媒が活性状態ではなくなった場合（排気浄化触媒の温度が活性温度より低くなった場合）も、触媒昇温制御の強度は元に戻される。 When the entire region of the oxidation catalyst becomes inactive or when a predetermined region near the downstream end of the oxidation catalyst becomes inactive, the strength of the catalyst temperature increase control is restored (oxidation catalyst and exhaust gas). The temperature of the purification catalyst can be increased when the temperature of the purification catalyst is raised from a state lower than the activation temperature to a state higher than the activation temperature. Further, when the exhaust purification catalyst is no longer in an active state (when the temperature of the exhaust purification catalyst becomes lower than the activation temperature), the strength of the catalyst temperature increase control is restored.

本発明において、
前記排気浄化触媒は、排気中のＮＯｘを浄化するＮＯｘ浄化触媒を含み、
前記制御手段は、前記ＮＯｘ浄化触媒の温度がＮＯｘ浄化触媒の活性温度より低い場合は、前記触媒昇温制御の強度を所定の強度に調節し、該所定の強度の触媒昇温制御により前記ＮＯｘ浄化触媒の温度がＮＯｘ浄化触媒の活性温度以上に上昇した場合は、前記ＮＯｘ浄化触媒の温度がＮＯｘ浄化触媒の活性温度以上かつ前記温度分布検出手段により検出される温度分布において少なくとも前記酸化触媒の下流端近傍の所定領域の温度が酸化触媒の活性温度以上であれば、前記触媒昇温制御の強度を前記所定の強度よりも弱い強度に調節するように、前記昇温強度調節手段を制御するようにしても良い。 In the present invention,
The exhaust purification catalyst includes a NOx purification catalyst that purifies NOx in the exhaust,
When the temperature of the NOx purification catalyst is lower than the activation temperature of the NOx purification catalyst, the control means adjusts the intensity of the catalyst temperature increase control to a predetermined intensity, and performs the NOx purification catalyst temperature increase control with the predetermined intensity. When the temperature of the purification catalyst rises above the activation temperature of the NOx purification catalyst, the temperature of the NOx purification catalyst is equal to or higher than the activation temperature of the NOx purification catalyst and at least in the temperature distribution detected by the temperature distribution detection means. If the temperature of the predetermined region near the downstream end is equal to or higher than the activation temperature of the oxidation catalyst, the temperature increase intensity adjusting means is controlled so that the intensity of the catalyst temperature increase control is adjusted to be weaker than the predetermined intensity. You may do it.

低温状態の酸化触媒にはＮＯｘが吸着し、酸化触媒の温度が上昇すると吸着しているＮＯｘが酸化触媒から脱離する。   NOx is adsorbed on the low-temperature oxidation catalyst, and the adsorbed NOx is desorbed from the oxidation catalyst when the temperature of the oxidation catalyst rises.

本発明では、ＮＯｘ浄化触媒がＮＯｘ浄化触媒の活性温度以上の状態を維持しながら、酸化触媒の一部の温度が活性温度より低い状態と活性温度以上の状態とが交互に現われる。酸化触媒が低温のときは排気中のＮＯｘが酸化触媒に吸着することによりＮＯｘのエミッションが低減する。   In the present invention, the state in which the temperature of a part of the oxidation catalyst is lower than the activation temperature and the state above the activation temperature alternately appear while the NOx purification catalyst maintains the state of the activation temperature or higher of the NOx purification catalyst. When the oxidation catalyst is at a low temperature, NOx emission is reduced by adsorbing NOx in the exhaust gas to the oxidation catalyst.

酸化触媒の温度が上昇したときは、酸化触媒から脱離したＮＯｘはＮＯｘ浄化触媒において浄化される（排気からＮＯｘが除去される）。   When the temperature of the oxidation catalyst rises, NOx desorbed from the oxidation catalyst is purified by the NOx purification catalyst (NOx is removed from the exhaust).

本発明の排気浄化装置によれば、高いＮＯｘ浄化率を達成できるとともに、触媒昇温制御に係るエネルギー消費を抑えることができるので、燃費性能の低下を抑制することも可能となる。   According to the exhaust purification apparatus of the present invention, a high NOx purification rate can be achieved, and energy consumption related to catalyst temperature increase control can be suppressed, so that it is possible to suppress a decrease in fuel efficiency.

上記構成において、
前記排気浄化触媒は、前記ＮＯｘ浄化触媒の上流側に設けられ、排気中の微粒子物質を捕集するとともに酸化触媒を有するフィルタを含み、
前記制御手段は、前記ＮＯｘ浄化触媒の温度がＮＯｘ浄化触媒の活性温度より低いか又は前記フィルタの温度がフィルタの活性温度より低い場合は、前記触媒昇温制御の強度を所定の強度に調節し、該所定の強度の触媒昇温制御により前記フィルタの温度がフィルタの活性温度以上に上昇し且つ前記ＮＯｘ浄化触媒の温度がＮＯｘ浄化触媒の活性温度以上に上昇した場合は、前記フィルタの温度がフィルタの活性温度以上かつ前記ＮＯｘ浄化触媒の温度がＮＯｘ浄化触媒の活性温度以上かつ前記温度分布検出手段により検出される温度分布において少なくとも前記酸化触媒の下流端近傍の所定領域の温度が酸化触媒の活性温度以上であれば、前記触媒昇温制御の強度を前記所定の強度よりも弱い強度に調節するように、前記昇温強度調節手段を制御するようにしても良い。 In the above configuration,
The exhaust purification catalyst includes a filter that is provided on the upstream side of the NOx purification catalyst and collects particulate matter in the exhaust and has an oxidation catalyst.
When the temperature of the NOx purification catalyst is lower than the activation temperature of the NOx purification catalyst or the temperature of the filter is lower than the activation temperature of the filter, the control means adjusts the intensity of the catalyst temperature increase control to a predetermined intensity. When the temperature of the filter rises above the activation temperature of the filter and the temperature of the NOx purification catalyst rises above the activation temperature of the NOx purification catalyst by the catalyst temperature increase control of the predetermined strength, the temperature of the filter is In the temperature distribution above the activation temperature of the filter and the temperature of the NOx purification catalyst is above the activation temperature of the NOx purification catalyst and detected by the temperature distribution detection means, at least the temperature in the predetermined region near the downstream end of the oxidation catalyst is the temperature of the oxidation catalyst. The temperature increase intensity adjusting means adjusts the intensity of the catalyst temperature increase control to an intensity weaker than the predetermined intensity if the activation temperature is higher than the activation temperature. It may be controlled.

この構成によれば、フィルタ及びＮＯｘ浄化触媒が活性状態であることを条件に、酸化触媒が部分的に非活性状態になることを許容するように、触媒昇温制御の強度を制御する。酸化触媒の一部領域が非活性状態となることを許容して触媒昇温制御を弱めることができるので、触媒昇温制御に係るエネルギー消費を抑えることができる。   According to this configuration, on the condition that the filter and the NOx purification catalyst are in the active state, the intensity of the catalyst temperature increase control is controlled so as to allow the oxidation catalyst to be partially inactivated. Since it is possible to weaken the catalyst temperature increase control while allowing a partial region of the oxidation catalyst to be in an inactive state, energy consumption related to the catalyst temperature increase control can be suppressed.

酸化触媒の全域が非活性状態となった場合には、触媒昇温制御の強度を元に戻す。また、フィルタ及びＮＯｘ浄化触媒が活性状態ではなくなった場合（フィルタの温度がフィルタの活性温度より低いか、又は、ＮＯｘ浄化触媒の温度がＮＯｘ浄化触媒の活性温度より低くなった場合）も、触媒昇温制御の強度は元に戻される。   When the entire area of the oxidation catalyst becomes inactive, the strength of the catalyst temperature increase control is restored. Further, when the filter and the NOx purification catalyst are no longer in an active state (when the temperature of the filter is lower than the activation temperature of the filter or the temperature of the NOx purification catalyst becomes lower than the activation temperature of the NOx purification catalyst), the catalyst The strength of the temperature rise control is restored.

なお、フィルタの活性温度はフィルタが有する酸化触媒の活性温度であり、「フィルタ及びＮＯｘ浄化触媒の温度が所定の活性温度以上」とは、「フィルタの温度がフィルタの酸化触媒の活性温度以上かつＮＯｘ浄化触媒の温度がＮＯｘ浄化触媒の活性温度以上」を意味するものとする。   The activation temperature of the filter is the activation temperature of the oxidation catalyst of the filter, and “the temperature of the filter and the NOx purification catalyst is equal to or higher than the predetermined activation temperature” means that “the temperature of the filter is equal to or higher than the activation temperature of the oxidation catalyst of the filter and It means that the temperature of the NOx purification catalyst is equal to or higher than the activation temperature of the NOx purification catalyst.

従って、フィルタ及びＮＯｘ浄化触媒が活性温度以上の状態を維持しながら、酸化触媒の一部の温度が活性温度より低い状態と活性温度以上の状態とが交互に現われる。上述のように、低温状態の酸化触媒は排気中のＮＯｘを吸着し、酸化触媒の温度が上昇すると吸着しているＮＯｘが酸化触媒から脱離する。   Therefore, while the filter and the NOx purification catalyst maintain the state of the activation temperature or higher, the state where the temperature of a part of the oxidation catalyst is lower than the activation temperature and the state of the activation temperature or higher appear alternately. As described above, the oxidation catalyst in the low temperature state adsorbs NOx in the exhaust gas, and the adsorbed NOx is desorbed from the oxidation catalyst when the temperature of the oxidation catalyst rises.

脱離したＮＯｘはフィルタの酸化触媒においてＮＯからＮＯ２を生成する酸化反応に関与する。これにより、特にＮＯｘ浄化触媒が選択還元型ＮＯｘ触媒の場合には、選択還元型ＮＯｘ触媒におけるアンモニアを還元剤とするＮＯｘの還元浄化反応に同程度の量のＮＯとＮＯ２が関与するようになり、高いＮＯｘ浄化率が得られる。 The desorbed NOx is involved in the oxidation reaction that generates NO 2 from NO in the oxidation catalyst of the filter. As a result, particularly when the NOx purification catalyst is a selective reduction type NOx catalyst, the same amount of NO and NO 2 are involved in the reduction purification reaction of NOx using ammonia as a reducing agent in the selective reduction type NOx catalyst. Thus, a high NOx purification rate can be obtained.

また、酸化触媒、フィルタ及び選択還元型ＮＯｘ触媒が直列配置された構成において、選択還元型ＮＯｘ触媒のＮＯｘ浄化率のＮＯ２に対する感度が低い場合には、フィルタにおいてＮＯがＮＯ２に酸化する反応が弱くなってもＮＯｘ浄化率への影響が小さいので、フィルタの一部が活性温度より低くなることを許容することができる。 Further, the oxidation catalyst, in the configuration in which the filter and the selective reduction type NOx catalyst is disposed in series, if less sensitive to NO 2 in the NOx purification rate of the selective reduction type NOx catalyst, NO in the filter is oxidized to NO 2 reaction Since the influence on the NOx purification rate is small even when the pressure becomes weak, it is possible to allow a part of the filter to be lower than the activation temperature.

この場合、フィルタについては、酸化触媒と同様に、少なくとも一部の領域が活性温度以上であれば他の領域が活性温度より低くなっても触媒昇温制御の強度を所定の強度より弱い強度に調節する制御を継続するよう判断しても良い。これにより、触媒昇温制御の強度を所定の強度より弱い強度に調節する制御を長期間実施できるので、燃費の抑制効果をより一層高めることができる。   In this case, for the filter, as in the case of the oxidation catalyst, if at least a part of the region is equal to or higher than the activation temperature, the strength of the catalyst temperature increase control is made weaker than the predetermined strength even if the other region is lower than the activation temperature. It may be determined to continue the control to be adjusted. Thereby, since the control for adjusting the strength of the catalyst temperature increase control to a strength weaker than the predetermined strength can be performed for a long period of time, the effect of suppressing fuel consumption can be further enhanced.

本発明において、
前記酸化触媒におけるＮＯｘの吸着量を検出するＮＯｘ吸着量検出手段を備え、
前記制御手段は、前記ＮＯｘ吸着量検出手段により検出されるＮＯｘの吸着量が所定量以上になったと判定された場合、前記触媒昇温制御の強度を前記所定の強度に調節するように前記昇温強度調節手段を制御しても良い。 In the present invention,
NOx adsorption amount detection means for detecting the NOx adsorption amount in the oxidation catalyst,
When it is determined that the NOx adsorption amount detected by the NOx adsorption amount detection unit has become equal to or greater than a predetermined amount, the controller is configured to adjust the intensity of the catalyst temperature increase control to the predetermined intensity. The temperature intensity adjusting means may be controlled.

言い換えると、酸化触媒及びＮＯｘ浄化触媒が直列配置された構成において、制御手段は、所定の強度の触媒昇温制御によりＮＯｘ浄化触媒の温度がＮＯｘ浄化触媒の活性温度以上に上昇した場合は、ＮＯｘ浄化触媒の温度がＮＯｘ浄化触媒の活性温度以上かつ温度分布検出手段により検出される温度分布において少なくとも酸化触媒の下流端近傍の所定領域の温度が酸化触媒の活性温度以上であって、更にＮＯｘ吸着量検出手段により検出される酸化触媒におけるＮＯｘの吸着量が所定量より少なければ、触媒昇温制御の強度を前記所定の強度よりも弱い強度に調節するように昇温強度調節手段を制御し、逆にＮＯｘ吸着量検出手段により検出される酸化触媒におけるＮＯｘの吸着量が所定量以上であれば、触媒昇温制御の強度を前記所定の強度に調節するように昇温強度調節手段を制御する。   In other words, in the configuration in which the oxidation catalyst and the NOx purification catalyst are arranged in series, when the temperature of the NOx purification catalyst rises above the activation temperature of the NOx purification catalyst by the catalyst temperature increase control with a predetermined strength, the control means In the temperature distribution in which the temperature of the purification catalyst is equal to or higher than the activation temperature of the NOx purification catalyst and detected by the temperature distribution detection means, at least the temperature in the predetermined region near the downstream end of the oxidation catalyst is equal to or higher than the activation temperature of the oxidation catalyst. If the amount of NOx adsorbed on the oxidation catalyst detected by the amount detection means is less than a predetermined amount, the temperature increase intensity adjusting means is controlled so as to adjust the intensity of the catalyst temperature increase control to be weaker than the predetermined intensity, Conversely, if the NOx adsorption amount detected by the NOx adsorption amount detecting means is equal to or greater than a predetermined amount, the intensity of the catalyst temperature rise control is set to the predetermined amount. Controlling the temperature increase intensity adjusting means to adjust the intensity.

また、酸化触媒、フィルタ及びＮＯｘ浄化触媒が直列配置された構成において、制御手段は、所定の強度の触媒昇温制御によりフィルタの温度がフィルタの活性温度以上に上昇し及びＮＯｘ浄化触媒の温度がＮＯｘ浄化触媒の活性温度以上に上昇した場合は、フィルタの温度がフィルタの活性温度以上かつＮＯｘ浄化触媒の温度がＮＯｘ浄化触媒の活性温度以上かつ温度分布検出手段により検出される温度分布において少なくとも酸化触媒の下流端近傍の所定領域の温度が酸化触媒の活性温度以上であって、更にＮＯｘ吸着量検出手段により検出される酸化触媒におけるＮＯｘの吸着量が所定量より少なければ、触媒昇温
制御の強度を前記所定の強度より弱い強度に調節するように昇温強度調節手段を制御し、逆にＮＯｘ吸着量検出手段により検出される酸化触媒におけるＮＯｘの吸着量が所定量以上であれば、触媒昇温制御の強度を前記所定の強度に調節するように昇温強度調節手段を制御する。 Further, in the configuration in which the oxidation catalyst, the filter and the NOx purification catalyst are arranged in series, the control means increases the temperature of the filter above the activation temperature of the filter by the catalyst temperature increase control with a predetermined strength, and the temperature of the NOx purification catalyst is increased. When the temperature rises above the activation temperature of the NOx purification catalyst, the temperature of the filter is above the activation temperature of the filter and the temperature of the NOx purification catalyst is above the activation temperature of the NOx purification catalyst and is at least oxidized in the temperature distribution detected by the temperature distribution detection means. If the temperature of the predetermined region near the downstream end of the catalyst is equal to or higher than the activation temperature of the oxidation catalyst and the NOx adsorption amount detected by the NOx adsorption amount detecting means is less than the predetermined amount, the catalyst temperature increase control is performed. The temperature rising intensity adjusting means is controlled so as to adjust the intensity to be weaker than the predetermined intensity, and conversely by the NOx adsorption amount detecting means. If the amount of adsorption of NOx on the oxidation catalyst to be detected is equal to or more than a predetermined amount, to control the temperature increase intensity adjusting means to adjust the strength of the catalyst Atsushi Nobori control to the predetermined strength.

所定量は、酸化触媒においてＮＯｘの吸着が飽和しているか否かを判定できるように定められる。酸化触媒におけるＮＯｘの吸着量は、酸化触媒に流入するＮＯｘ量や酸化触媒の温度に基づいて推定することができる。   The predetermined amount is determined so that it can be determined whether or not NOx adsorption is saturated in the oxidation catalyst. The adsorption amount of NOx in the oxidation catalyst can be estimated based on the amount of NOx flowing into the oxidation catalyst and the temperature of the oxidation catalyst.

本発明において、前記排気浄化触媒が、所定の温度範囲において活性化するとともに該温度範囲より温度が高い場合及び低い場合には非活性となる触媒を含む場合は、
前記制御手段は、前記触媒昇温制御の強度を前記所定の強度又は前記所定の強度より弱い強度に調節するように前記昇温強度調節手段を制御しているときに、前記触媒の温度が前記温度範囲より高くなった場合は、前記触媒昇温制御を停止するよう前記触媒昇温手段を制御しても良い。 In the present invention, when the exhaust purification catalyst includes a catalyst that is activated in a predetermined temperature range and deactivated when the temperature is higher and lower than the temperature range,
The control means controls the temperature rise intensity adjusting means so as to adjust the intensity of the catalyst temperature rise control to the predetermined intensity or weaker than the predetermined intensity. When the temperature is higher than the temperature range, the catalyst temperature raising means may be controlled to stop the catalyst temperature raising control.

ここで、「活性化」とは、排気浄化触媒が排気中の所定の成分に対して所望の排気浄化能力を発揮することが可能な状態を意味する。また、「非活性」とは、排気浄化触媒が排気中の所定の成分に対して所望の排気浄化能力を発揮することができない状態を意味する。   Here, “activation” means a state in which the exhaust purification catalyst can exhibit a desired exhaust purification capability with respect to a predetermined component in the exhaust. Further, “inactive” means a state in which the exhaust purification catalyst cannot exhibit a desired exhaust purification capability for a predetermined component in the exhaust.

従って、「所定の温度範囲において活性化するとともに該温度範囲より温度が高い場合及び低い場合には非活性となる触媒」とは、「所定の温度範囲において所定の排気浄化能力を発揮するとともに該温度範囲より温度が高い場合及び低い場合には所定の排気浄化能力を発揮することができない触媒」又は「所定の温度範囲において排気浄化率が所定値以上となり、それ以外の温度において排気浄化率が所定値より低くなる触媒」と捉えることができる。   Therefore, “a catalyst that is activated in a predetermined temperature range and deactivated when the temperature is higher and lower than the temperature range” means that “a catalyst that exhibits a predetermined exhaust purification capability in a predetermined temperature range and that is inactive. When the temperature is higher or lower than the temperature range, the catalyst is unable to exhibit the predetermined exhaust purification ability ”or“ the exhaust purification rate exceeds a predetermined value in the predetermined temperature range, and the exhaust purification rate is at other temperatures. It can be understood that the catalyst is lower than a predetermined value.

すなわち、排気浄化触媒の温度が活性下限温度より低い場合には所定の強度で触媒昇温制御を行い、排気浄化触媒の温度が活性温度範囲内の温度である場合には、酸化触媒の下流端近傍の所定領域の温度が活性温度以上であることを条件に触媒昇温制御の強度を前記所定の強度より弱い強度に調節し、ＮＯｘ浄化触媒の温度が活性上限温度より高い場合には触媒昇温制御を停止する。   That is, when the temperature of the exhaust purification catalyst is lower than the activation lower limit temperature, the catalyst temperature increase control is performed with a predetermined intensity, and when the temperature of the exhaust purification catalyst is within the activation temperature range, the downstream end of the oxidation catalyst. The temperature of the catalyst temperature increase control is adjusted to be weaker than the predetermined intensity on the condition that the temperature of the predetermined region in the vicinity is equal to or higher than the activation temperature. Stop temperature control.

ここで、「活性下限温度」とは、排気浄化触媒が排気中の所定の成分に対して所望の排気浄化能力を発揮することが可能な温度の下限値を意味する。「活性上限温度」とは、排気浄化触媒が排気中の所定の成分に対して所望の排気浄化能力を発揮することが可能な温度の上限値を意味する。   Here, the “lower limit temperature of activation” means the lower limit value of the temperature at which the exhaust purification catalyst can exhibit a desired exhaust purification capability for a predetermined component in the exhaust. “Activity upper limit temperature” means an upper limit value of a temperature at which the exhaust purification catalyst can exhibit a desired exhaust purification capability for a predetermined component in the exhaust.

「所定の成分」とは、その排気浄化触媒により排気中から除去することを意図されている成分であり、例えばＮＯｘ浄化触媒であればＮＯｘである。「所望の排気浄化能力」とは、規制等を考慮して設計段階である値に設定される浄化率などである。   The “predetermined component” is a component intended to be removed from the exhaust gas by the exhaust purification catalyst. For example, in the case of a NOx purification catalyst, it is NOx. The “desired exhaust purification capacity” is a purification rate set to a value at a design stage in consideration of regulations and the like.

例えばアンモニアを還元剤として排気中のＮＯｘを選択的に還元浄化する選択還元型ＮＯｘ触媒の場合、触媒温度が高温になり過ぎるとアンモニアが選択還元型ＮＯｘ触媒に吸着しにくくなるために所望のＮＯｘ浄化率が得られなくなる。   For example, in the case of a selective reduction type NOx catalyst that selectively reduces and purifies NOx in exhaust gas using ammonia as a reducing agent, if the catalyst temperature becomes too high, ammonia becomes difficult to be adsorbed on the selective reduction type NOx catalyst. A purification rate cannot be obtained.

上記構成によれば、触媒温度が、所望の排気浄化能力を発揮できないほど高温になったと判定される場合には触媒昇温制御が停止されるので、上記選択還元型ＮＯｘ触媒のように触媒温度が高温になりすぎると所望の排気浄化能力を発揮できない触媒においても、所
望の排気浄化能力が発揮される状態を好適に維持することができる。 According to the above configuration, when it is determined that the catalyst temperature has become so high that the desired exhaust purification capability cannot be exhibited, the catalyst temperature increase control is stopped, so that the catalyst temperature as in the selective reduction type NOx catalyst is stopped. Even in a catalyst that cannot exhibit the desired exhaust purification ability when the temperature becomes too high, the state in which the desired exhaust purification ability is exhibited can be suitably maintained.

このようにある活性下限温度から活性上限温度までの温度範囲内で所望の排気浄化能力を発揮することができる排気浄化触媒の場合、これまで述べた本発明の各構成における「排気浄化触媒の活性温度」を、上記の意味での活性下限温度として捉えることができる。その場合、本発明の各構成における「排気浄化触媒が活性温度以上」とは、排気浄化触媒が活性下限温度以上ということであって、活性温度範囲を超えた（活性上限温度より高い）温度ということではない。   In the case of the exhaust purification catalyst capable of exhibiting a desired exhaust purification capability within a temperature range from a certain activity lower limit temperature to the activity upper limit temperature, the “activity of the exhaust purification catalyst in each configuration of the present invention described so far” is described. “Temperature” can be taken as the lower limit of activity in the above sense. In that case, “the exhaust purification catalyst is at or above the activation temperature” in each configuration of the present invention means that the exhaust purification catalyst is at or above the activation lower limit temperature, which is a temperature exceeding the activation temperature range (higher than the activation upper limit temperature). Not that.

本発明において、前記排気浄化触媒、アンモニアを吸着して排気中のＮＯｘを選択的に還元浄化する選択還元型ＮＯｘ触媒を含む場合は、
前記内燃機関の排気浄化装置は、
前記選択還元型ＮＯｘ触媒の温度及びアンモニア吸着量に基づいて前記選択還元型ＮＯｘ触媒からアンモニアが流出するアンモニアスリップの発生条件が成立するか判定するアンモニアスリップ発生判定手段を更に備え、
前記制御手段は、前記触媒昇温制御の強度を前記所定の強度又は前記所定の強度より弱い強度に調節するように前記昇温強度調節手段を制御しているときに、前記アンモニアスリップ発生判定手段によりアンモニアスリップの発生条件が成立すると判定された場合は、前記触媒昇温制御を停止するよう前記触媒昇温手段を制御しても良い。 In the present invention, when the exhaust purification catalyst includes a selective reduction type NOx catalyst that adsorbs ammonia and selectively reduces and purifies NOx in the exhaust,
The exhaust gas purification device for the internal combustion engine includes:
Ammonia slip generation determination means for determining whether an ammonia slip generation condition in which ammonia flows out of the selective reduction NOx catalyst is satisfied based on the temperature of the selective reduction NOx catalyst and the ammonia adsorption amount;
The control means controls the temperature rise intensity adjusting means so as to adjust the intensity of the catalyst temperature rise control to the predetermined intensity or an intensity weaker than the predetermined intensity. When it is determined that the conditions for generating ammonia slip are satisfied, the catalyst temperature raising means may be controlled to stop the catalyst temperature raising control.

選択還元型ＮＯｘ触媒は触媒に吸着するアンモニアがＮＯｘの還元浄化作用をなす。そして選択還元型ＮＯｘ触媒に吸着可能なアンモニアの量は触媒温度が高くなるほど減少する。そのため、選択還元型ＮＯｘ触媒に多量のアンモニアが吸着している状態で触媒温度が上昇した場合、吸着できなくなったアンモニアが脱離してアンモニアスリップを発生させる可能性がある。   In the selective reduction type NOx catalyst, ammonia adsorbed on the catalyst performs a reduction and purification action of NOx. The amount of ammonia that can be adsorbed on the selective reduction type NOx catalyst decreases as the catalyst temperature increases. Therefore, when the catalyst temperature rises in a state where a large amount of ammonia is adsorbed on the selective reduction type NOx catalyst, ammonia that cannot be adsorbed may be desorbed and ammonia slip may occur.

上記構成によれば、このようなアンモニアスリップが発生する可能性があると判断できるアンモニアスリップの発生条件が成立する場合には、触媒昇温制御が停止されるので、アンモニアスリップの発生を好適に抑制することができる。   According to the above configuration, when the ammonia slip generation condition that can be determined to cause such ammonia slip is satisfied, the catalyst temperature increase control is stopped. Can be suppressed.

選択還元型ＮＯｘ触媒におけるアンモニアの吸着量は、選択還元型ＮＯｘ触媒より上流の排気に添加されるアンモニアや尿素の量、内燃機関の運転状態、選択還元型ＮＯｘ触媒の温度、選択還元型ＮＯｘ触媒に流入するＮＯｘ量、選択還元型ＮＯｘ触媒から流出するＮＯｘ量などに基づいて検出することが可能である。   The adsorption amount of ammonia in the selective reduction type NOx catalyst is the amount of ammonia or urea added to the exhaust upstream of the selective reduction type NOx catalyst, the operating state of the internal combustion engine, the temperature of the selective reduction type NOx catalyst, the selective reduction type NOx catalyst. Detection based on the amount of NOx flowing into the catalyst, the amount of NOx flowing out from the selective reduction type NOx catalyst, and the like.

本発明において、前記触媒昇温手段は、燃料を噴射する燃料噴射手段と、該噴射された燃料に着火する着火手段と、を有し、前記酸化触媒より上流の排気の温度を上昇させるバーナであってもよい。   In the present invention, the catalyst temperature raising means includes a fuel injection means for injecting fuel and an ignition means for igniting the injected fuel, and is a burner for raising the temperature of the exhaust gas upstream from the oxidation catalyst. There may be.

このようなバーナを用いた場合、内燃機関から排出される未燃ＨＣやＣＯの浄化率が大幅に高くなる。本発明においては酸化触媒の一部が非活性状態となることが許容されるため、酸化触媒によるＨＣやＣＯの浄化作用が低下する場合が考えられるが、バーナを用いることによってシステム全体としてのＨＣやＣＯの浄化率が低下することを抑制できる。   When such a burner is used, the purification rate of unburned HC and CO discharged from the internal combustion engine is significantly increased. In the present invention, since a part of the oxidation catalyst is allowed to be in an inactive state, there may be a case where the HC or CO purification action by the oxidation catalyst is lowered. It can suppress that the purification rate of CO and CO fall.

本発明において、前記昇温強度調節手段は、前記燃料噴射手段により噴射される燃料量を調節することにより触媒昇温制御の強度を調節するようにしても良い。   In the present invention, the temperature increase intensity adjusting means may adjust the intensity of the catalyst temperature increase control by adjusting the amount of fuel injected by the fuel injection means.

この場合、触媒昇温制御の強度を弱める制御は、燃料噴射手段による燃料噴射量を減少させる制御になるので、触媒昇温制御の強度を弱めることにより昇温制御に係る燃料消費量を低減することができる。   In this case, the control for reducing the strength of the catalyst temperature increase control is a control for reducing the fuel injection amount by the fuel injection means. Therefore, by reducing the strength of the catalyst temperature increase control, the fuel consumption related to the temperature increase control is reduced. be able to.

上記構成において、前記温度分布検出手段は、前記酸化触媒を複数の領域に分割した場合の各領域の温度を検出するようにしても良い。   In the above configuration, the temperature distribution detection means may detect the temperature of each region when the oxidation catalyst is divided into a plurality of regions.

各領域の温度は各領域の酸化触媒における位置や内燃機関の運転状態に基づく推定により検出することもできるし、温度センサによって直接検出することもできる。   The temperature of each region can be detected by estimation based on the position of the oxidation catalyst in each region and the operating state of the internal combustion engine, or can be detected directly by a temperature sensor.

本発明によれば、排気通路に配置される排気浄化触媒を昇温させる制御において燃費の悪化を抑制す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が可能になる。   ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the exhaust gas purification apparatus of the internal combustion engine which can suppress the deterioration of a fuel consumption in the control which heats up the exhaust gas purification catalyst arrange | positioned at an exhaust passage.

実施例に係る内燃機関の排気浄化システムの概略構成を示す図である。It is a figure which shows schematic structure of the exhaust gas purification system of the internal combustion engine which concerns on an Example. 実施例に係る内燃機関の排気浄化システムにおけるバーナの概略構成を示す図である。It is a figure which shows schematic structure of the burner in the exhaust gas purification system of the internal combustion engine which concerns on an Example. 実施例に係る内燃機関の排気浄化システムにおいて触媒昇温制御を行う場合の温度制御を説明するための図である。It is a figure for demonstrating the temperature control in the case of performing catalyst temperature rising control in the exhaust gas purification system of the internal combustion engine which concerns on an Example. 実施例に係る内燃機関の排気浄化システムにおける酸化触媒の領域分割を示す図である。It is a figure which shows the area | region division | segmentation of the oxidation catalyst in the exhaust gas purification system of the internal combustion engine which concerns on an Example. 実施例に係る内燃機関の排気浄化システムにおける他の触媒昇温制御を行う場合の温度制御を説明するための図である。It is a figure for demonstrating the temperature control in the case of performing the other catalyst temperature rising control in the exhaust gas purification system of the internal combustion engine which concerns on an Example. 実施例に係る内燃機関の排気浄化システムの触媒昇温制御を行った場合の触媒昇温制御の強度、選択還元型ＮＯｘ触媒の温度、酸化触媒の温度及び酸化触媒におけるＮＯｘ吸着量の時間変化の一例を示す図である。FIG. 6 shows the time variation of the intensity of catalyst temperature rise control, the temperature of the selective reduction type NOx catalyst, the temperature of the oxidation catalyst, and the NOx adsorption amount in the oxidation catalyst when the catalyst temperature rise control of the exhaust purification system of the internal combustion engine according to the embodiment is performed It is a figure which shows an example. 実施例に係る内燃機関の排気浄化システムの触媒昇温制御を表すフローチャートである。It is a flowchart showing the catalyst temperature increase control of the exhaust gas purification system of the internal combustion engine according to the embodiment. 実施例に係る内燃機関の排気浄化システムの他の触媒昇温制御を表すフローチャートである。It is a flowchart showing the other catalyst temperature rising control of the exhaust gas purification system of the internal combustion engine which concerns on an Example. 選択還元型ＮＯｘ触媒の温度と吸着可能なアンモニアの量との関係を示す図である。It is a figure which shows the relationship between the temperature of a selective reduction type NOx catalyst, and the quantity of ammonia which can be adsorbed.

以下、本発明の実施の形態について、詳細に説明する。本実施例に記載されている構成部品の寸法、材質、形状、その相対配置等は、特に記載がない限りは、発明の技術的範囲をそれらのみに限定する趣旨のものではない。   Hereinafter, embodiments of the present invention will be described in detail. The dimensions, materials, shapes, relative arrangements, and the like of the components described in the present embodiment are not intended to limit the technical scope of the invention to those unless otherwise specified.

図１は本実施例に係る内燃機関の排気浄化システムの概略構成を示す図である。図１において、エンジン１には既燃ガスが排出される排気通路２が接続される。排気通路２にはエンジン１に近い側から順に、酸化触媒４、排気中の微粒子物質を捕集するとともに酸化触媒を有するフィルタ５と、アンモニアを還元剤として排気中のＮＯｘを選択的に還元浄化する選択還元型ＮＯｘ触媒６（ＮＯｘ浄化触媒）と、が備わる。   FIG. 1 is a diagram showing a schematic configuration of an exhaust gas purification system for an internal combustion engine according to the present embodiment. In FIG. 1, an exhaust passage 2 through which burned gas is discharged is connected to an engine 1. In order from the side closer to the engine 1 to the exhaust passage 2, the oxidation catalyst 4, the filter 5 having the oxidation catalyst as well as the particulate matter in the exhaust, and the NOx in the exhaust are selectively reduced and purified using ammonia as a reducing agent. And a selective reduction type NOx catalyst 6 (NOx purification catalyst).

選択還元型ＮＯｘ触媒６より上流側の排気通路２には、排気中に尿素水を噴射する尿素添加弁７が備わる。尿素添加弁７から排気中に噴射された尿素水は、排気中で分解してアンモニア（ＮＨ３）を生成する。このアンモニアが選択還元型ＮＯｘ触媒６において還元剤として作用する。尿素添加弁７による尿素水の噴射はＥＣＵ１３によって制御される。 The exhaust passage 2 upstream of the selective reduction type NOx catalyst 6 is provided with a urea addition valve 7 for injecting urea water into the exhaust. The urea water injected into the exhaust gas from the urea addition valve 7 is decomposed in the exhaust gas to generate ammonia (NH 3 ). This ammonia acts as a reducing agent in the selective reduction type NOx catalyst 6. The injection of urea water by the urea addition valve 7 is controlled by the ECU 13.

酸化触媒４、フィルタ５の酸化触媒、選択還元型ＮＯｘ触媒６は、それぞれの触媒作用が活性化する活性温度があり、これらの触媒によって排気浄化を行うためには各触媒の温度を各触媒の活性温度以上に昇温する必要がある。本実施例の排気浄化システムでは、酸
化触媒４、フィルタ５及び選択還元型ＮＯｘ触媒６を昇温するために、酸化触媒４より上流側にバーナ３が設けられる。 The oxidation catalyst 4, the oxidation catalyst of the filter 5, and the selective reduction type NOx catalyst 6 have activation temperatures at which the catalytic action is activated, and in order to perform exhaust purification using these catalysts, the temperature of each catalyst is set to each catalyst's temperature. It is necessary to raise the temperature above the activation temperature. In the exhaust purification system of this embodiment, the burner 3 is provided upstream of the oxidation catalyst 4 in order to raise the temperature of the oxidation catalyst 4, the filter 5 and the selective reduction type NOx catalyst 6.

図２はバーナ３の概略構成を示す図である。図２に示すように、バーナ３は、バーナ燃焼室１７、空気供給通路１６、エアポンプ１８、燃料噴射弁１４（燃料添加手段）、点火プラグ１５（着火手段）を備えている。図２の排気通路２に描かれている矢印は排気通路２における排気の流れを示す。   FIG. 2 is a diagram showing a schematic configuration of the burner 3. As shown in FIG. 2, the burner 3 includes a burner combustion chamber 17, an air supply passage 16, an air pump 18, a fuel injection valve 14 (fuel addition means), and an ignition plug 15 (ignition means). The arrows drawn in the exhaust passage 2 in FIG. 2 indicate the flow of exhaust in the exhaust passage 2.

図２に示すように、バーナ燃焼室１７は排気通路２内に突出するように設置され、バーナ燃焼室１７の排気通路２に突出した端部は排気通路２に開放している。バーナ燃焼室１７にはエアポンプ１８によって圧送された二次空気が空気供給通路１６を通して供給される。   As shown in FIG. 2, the burner combustion chamber 17 is installed so as to protrude into the exhaust passage 2, and the end of the burner combustion chamber 17 protruding into the exhaust passage 2 is open to the exhaust passage 2. Secondary air pressure-fed by an air pump 18 is supplied to the burner combustion chamber 17 through an air supply passage 16.

ここで二次空気とは、排気とは別にバーナ燃焼室１７に供給される空気である。燃料噴射弁１４はバーナ燃焼室１７内に燃料を噴射する。バーナ燃焼室１７内では、燃料噴射弁１４から噴射される燃料と空気供給通路１６から供給される空気とが混合して形成される混合気に点火プラグ１５による点火が行われることで、燃料が燃焼し火炎が形成される。   Here, the secondary air is air supplied to the burner combustion chamber 17 separately from the exhaust. The fuel injection valve 14 injects fuel into the burner combustion chamber 17. In the burner combustion chamber 17, ignition is performed by the spark plug 15 on the air-fuel mixture formed by mixing the fuel injected from the fuel injection valve 14 and the air supplied from the air supply passage 16, so that the fuel is Burns and forms a flame.

この火炎の熱によって排気が加熱される。燃料噴射弁１４、点火プラグ１５及びエアポンプ１８の動作はＥＣＵ１３によって制御される。   The exhaust is heated by the heat of the flame. The operations of the fuel injection valve 14, the spark plug 15, and the air pump 18 are controlled by the ECU 13.

図１に戻り、酸化触媒４の下流側の排気通路２には酸化触媒４から流出する排気の温度を検出する排気温度センサ８が備わる。フィルタ５の下流側の排気通路２にはフィルタ５から流出する排気の温度を検出する排気温度センサ９が備わる。   Returning to FIG. 1, the exhaust passage 2 downstream of the oxidation catalyst 4 is provided with an exhaust temperature sensor 8 that detects the temperature of the exhaust gas flowing out from the oxidation catalyst 4. The exhaust passage 2 on the downstream side of the filter 5 is provided with an exhaust temperature sensor 9 that detects the temperature of the exhaust gas flowing out from the filter 5.

選択還元型ＮＯｘ触媒６の下流側の排気通路２には選択還元型ＮＯｘ触媒６から流出する排気の温度を検出する排気温度センサ１０が備わる。各排気温度センサによる検出値はＥＣＵ１３に入力される。ＥＣＵ１３は排気温度センサ８による検出値に基づいて酸化触媒４の温度を取得し、排気温度センサ９による検出値に基づいてフィルタ５の温度を取得し、排気温度センサ１０による検出値に基づいて選択還元型ＮＯｘ触媒６の温度を検出する。   The exhaust passage 2 on the downstream side of the selective reduction type NOx catalyst 6 is provided with an exhaust temperature sensor 10 that detects the temperature of the exhaust gas flowing out from the selective reduction type NOx catalyst 6. The detection value from each exhaust temperature sensor is input to the ECU 13. The ECU 13 acquires the temperature of the oxidation catalyst 4 based on the detection value by the exhaust temperature sensor 8, acquires the temperature of the filter 5 based on the detection value by the exhaust temperature sensor 9, and selects based on the detection value by the exhaust temperature sensor 10. The temperature of the reduced NOx catalyst 6 is detected.

選択還元型ＮＯｘ触媒６の上流側の排気通路２には選択還元型ＮＯｘ触媒６に流入する排気中のＮＯｘ量を検出するＮＯｘセンサ１１が備わり、選択還元型ＮＯｘ触媒６の下流側の排気通路２には選択還元型ＮＯｘ触媒６から流出する排気中のＮＯｘ量を検出するＮＯｘセンサ１２が備わる。   The exhaust passage 2 on the upstream side of the selective reduction type NOx catalyst 6 is provided with a NOx sensor 11 for detecting the amount of NOx in the exhaust gas flowing into the selective reduction type NOx catalyst 6, and the exhaust passage on the downstream side of the selective reduction type NOx catalyst 6. 2 includes a NOx sensor 12 that detects the amount of NOx in the exhaust gas flowing out from the selective reduction type NOx catalyst 6.

各ＮＯｘセンサによる検出値はＥＣＵ１３に入力される。ＥＣＵ１３はＮＯｘセンサ１１及びＮＯｘセンサ１２から入力される検出値に基づいて選択還元型ＮＯｘ触媒６によるＮＯｘ浄化率を算出する。   The detection value by each NOx sensor is input to the ECU 13. The ECU 13 calculates the NOx purification rate by the selective reduction type NOx catalyst 6 based on the detection values input from the NOx sensor 11 and the NOx sensor 12.

ＥＣＵ１３はエンジン１の運転状態を制御するコンピュータである。ＥＣＵ１３には上述した排気温度センサ８、９及び１０、ＮＯｘセンサ１１及び１２の他、不図示のクランク角度センサやアクセル開度センサなどの各種センサが接続され、各種センサによる検出値が入力される。   The ECU 13 is a computer that controls the operating state of the engine 1. In addition to the exhaust temperature sensors 8, 9 and 10 and the NOx sensors 11 and 12 described above, the ECU 13 is connected to various sensors such as a crank angle sensor and an accelerator opening sensor (not shown), and values detected by the various sensors are input. .

ＥＣＵ１３は各種センサから入力される検出値に基づいてエンジン１の運転状態や運転者の要求を取得し、それに基づいて上述した尿素添加弁７、バーナ３の燃料噴射弁１４、点火プラグ１５及びエアポンプ１８の他、エンジン１の不図示の燃料噴射弁などの各種機器の動作を制御する。   The ECU 13 obtains the operating state of the engine 1 and the driver's request based on the detection values input from various sensors, and based on that, the urea addition valve 7, the fuel injection valve 14 of the burner 3, the spark plug 15, and the air pump. 18, the operation of various devices such as a fuel injection valve (not shown) of the engine 1 is controlled.

ＥＣＵ１３は、フィルタ５の温度をフィルタ５の酸化触媒の活性温度以上に昇温させるとともに選択還元型ＮＯｘ触媒６の温度を選択還元型ＮＯｘ触媒６の活性温度以上に昇温させるために、バーナ３を作動させて酸化触媒４に流入する排気の温度を上昇させる。   The ECU 13 raises the temperature of the filter 5 above the activation temperature of the oxidation catalyst of the filter 5 and increases the temperature of the selective reduction NOx catalyst 6 above the activation temperature of the selective reduction NOx catalyst 6. To increase the temperature of the exhaust gas flowing into the oxidation catalyst 4.

本実施例ではバーナ３を作動させて酸化触媒４に流入する排気の温度を上昇させる制御が本発明における「触媒昇温制御」に相当し、バーナ３が「触媒昇温手段」として機能している。   In this embodiment, the control for operating the burner 3 to raise the temperature of the exhaust gas flowing into the oxidation catalyst 4 corresponds to the “catalyst temperature raising control” in the present invention, and the burner 3 functions as “catalyst temperature raising means”. Yes.

図３は、図１で説明したような酸化触媒４、フィルタ５及び選択還元型ＮＯｘ触媒６が排気通路２に直列配置されている排気浄化システムにおいてフィルタ５及び選択還元型ＮＯｘ触媒６を活性温度以上に昇温させる場合の各触媒の温度を示す図である。   3 shows the activation temperature of the filter 5 and the selective reduction type NOx catalyst 6 in the exhaust purification system in which the oxidation catalyst 4, the filter 5 and the selective reduction type NOx catalyst 6 are arranged in series in the exhaust passage 2 as described in FIG. It is a figure which shows the temperature of each catalyst in the case of heating up above.

図３において横軸は排気通路２における各触媒の位置を表し、右側ほどエンジン１からの距離が遠い。図３の縦軸は温度を表す。図３の実線Ａは、一般的な触媒昇温制御の場合の各触媒の温度を表す。   In FIG. 3, the horizontal axis represents the position of each catalyst in the exhaust passage 2, and the distance from the engine 1 is farther to the right. The vertical axis in FIG. 3 represents temperature. A solid line A in FIG. 3 represents the temperature of each catalyst in the case of general catalyst temperature increase control.

図３の実線Ａに示すように、直列配置されている複数の触媒は下流側ほど放熱によって温度が低下するため、最下流側に配置された選択還元型ＮＯｘ触媒６を選択還元型ＮＯｘ触媒６の活性温度以上に昇温するとともに、中程に配置されたフィルタ５をフィルタ５の酸化触媒の活性温度以上に昇温するために、上流側にある酸化触媒４をフィルタ５や選択還元型ＮＯｘ触媒６の活性温度よりも更に高い温度まで昇温させる。   As shown by a solid line A in FIG. 3, the temperature of the plurality of catalysts arranged in series decreases due to heat radiation toward the downstream side. Therefore, the selective reduction type NOx catalyst 6 arranged on the most downstream side is replaced with the selective reduction type NOx catalyst 6. In order to raise the temperature of the filter 5 disposed in the middle to a temperature higher than the activation temperature of the oxidation catalyst of the filter 5, the oxidation catalyst 4 on the upstream side is filtered with the filter 5 or the selective reduction type NOx. The temperature is raised to a temperature higher than the activation temperature of the catalyst 6.

そのため、酸化触媒４は過剰に昇温されていることになり、燃費性能が低下する原因となる場合がある。   Therefore, the temperature of the oxidation catalyst 4 is excessively increased, which may cause a reduction in fuel consumption performance.

これに対し、本実施例の排気浄化システムでは、図４に示すように、酸化触媒４を排気の流れ方向で３つの領域Ｘ１，Ｘ２及びＸ３に分けて考え、排気の流れ方向の酸化触媒４の温度分布を考える。   In contrast, in the exhaust purification system of the present embodiment, as shown in FIG. 4, the oxidation catalyst 4 is divided into three regions X1, X2, and X3 in the exhaust flow direction, and the oxidation catalyst 4 in the exhaust flow direction is considered. Consider the temperature distribution.

そして、所定の強度に調節された触媒昇温制御により一旦フィルタ５及び選択還元型ＮＯｘ触媒６が活性温度以上に昇温した場合、フィルタ５及び選択還元型ＮＯｘ触媒６の温度が活性温度以上であることを条件に、酸化触媒４の３つの領域のうち下流端の領域Ｘ３以外の領域の温度（領域Ｘ１及びＸ２の温度）が酸化触媒４の活性温度より低くなること、すなわち非活性状態となることを許容することとした。   When the temperature of the filter 5 and the selective reduction NOx catalyst 6 is once raised to the activation temperature or higher by the catalyst temperature increase control adjusted to a predetermined strength, the temperature of the filter 5 and the selective reduction NOx catalyst 6 is higher than the activation temperature. On the condition that the temperature of the three regions of the oxidation catalyst 4 other than the region X3 at the downstream end (the temperatures of the regions X1 and X2) is lower than the activation temperature of the oxidation catalyst 4, that is, the inactive state. It was allowed to be.

つまり、所定の強度に調節された触媒昇温制御により一旦フィルタ５及び選択還元型ＮＯｘ触媒６が活性温度以上に昇温した場合、フィルタ５又は選択還元型ＮＯｘ触媒６の温度が活性温度より低くなるか、又は、酸化触媒４の下流端の領域Ｘ３の温度が活性温度より低くなるまでの期間は、触媒昇温制御の強度を前記所定の強度よりも弱い強度に調節する。   That is, when the temperature of the filter 5 and the selective reduction type NOx catalyst 6 is once raised to the activation temperature or higher by the catalyst temperature rise control adjusted to a predetermined strength, the temperature of the filter 5 or the selective reduction type NOx catalyst 6 is lower than the activation temperature. Or during the period until the temperature of the downstream end region X3 of the oxidation catalyst 4 becomes lower than the activation temperature, the intensity of the catalyst temperature increase control is adjusted to be weaker than the predetermined intensity.

ここで、触媒昇温制御の強度を弱めるために、本実施例の場合には、バーナ３による排気の加熱の強度を弱める。具体的には、バーナ３の燃料噴射弁１４による燃料噴射量を減少させることによって触媒昇温制御の強度を弱める。   Here, in order to weaken the intensity of the catalyst temperature increase control, in the present embodiment, the intensity of heating of the exhaust by the burner 3 is weakened. Specifically, the strength of the catalyst temperature increase control is weakened by decreasing the fuel injection amount by the fuel injection valve 14 of the burner 3.

バーナ３による排気の加熱の強度を弱めると、酸化触媒４の温度は低下する。しかしながら、酸化触媒４の温度は上流側の領域Ｘ１から徐々に低下していくので、バーナ３の加熱強度が弱められてからしばらくの間は、上流側の領域Ｘ１やＸ２が活性温度より低くなって非活性であるものの、下流端の領域Ｘ３は活性温度以上で活性化している、という状
態になる。 When the intensity of the exhaust heating by the burner 3 is weakened, the temperature of the oxidation catalyst 4 is lowered. However, since the temperature of the oxidation catalyst 4 gradually decreases from the upstream region X1, the upstream regions X1 and X2 become lower than the activation temperature for a while after the heating intensity of the burner 3 is weakened. Although it is inactive, the downstream end region X3 is activated above the activation temperature.

本実施例の排気浄化システムでは、このように酸化触媒４の一部領域（下流端領域Ｘ３以外の領域）が非活性状態になることを許容する。本実施例において、少なくとも領域Ｘ３が活性化している状態が、本発明における「酸化触媒の少なくとも下流端近傍の所定領域が活性化している状態」に相当し、この状態には上流側の領域Ｘ１やＸ２が非活性状態（温度が酸化触媒４の活性温度より低い状態）が含まれる。   In the exhaust purification system of the present embodiment, the partial region (region other than the downstream end region X3) of the oxidation catalyst 4 is allowed to become inactive as described above. In this embodiment, the state where at least the region X3 is activated corresponds to the “state where at least the predetermined region near the downstream end of the oxidation catalyst is activated” in the present invention, and this state includes the upstream region X1. And X2 is inactive (a state where the temperature is lower than the activation temperature of the oxidation catalyst 4).

本実施例の排気浄化システムにおいて、酸化触媒４の一部領域が非活性状態になることを許容するのは、フィルタ５及び選択還元型ＮＯｘ触媒６の温度が活性温度以上であることを条件としている。すなわち、図３の破線Ｂで表されるような温度状態である。   In the exhaust purification system of the present embodiment, it is allowed that the partial region of the oxidation catalyst 4 is in an inactive state on condition that the temperature of the filter 5 and the selective reduction type NOx catalyst 6 is equal to or higher than the activation temperature. Yes. That is, the temperature state is represented by a broken line B in FIG.

本実施例の排気浄化システムでは、フィルタ５又は選択還元型ＮＯｘ触媒６が活性温度より低い場合には、実線Ａで表すように酸化触媒４、フィルタ５及び選択還元型ＮＯｘ触媒６の全てを昇温させることを目的として調節される比較的強い強度である所定の強度によって触媒昇温制御を行うことで、フィルタ５及び選択還元型ＮＯｘ触媒６を活性化させる。   In the exhaust purification system of this embodiment, when the filter 5 or the selective reduction type NOx catalyst 6 is lower than the activation temperature, all of the oxidation catalyst 4, the filter 5 and the selective reduction type NOx catalyst 6 are increased as shown by the solid line A. The filter 5 and the selective reduction type NOx catalyst 6 are activated by performing catalyst temperature increase control with a predetermined intensity which is a relatively strong intensity adjusted for the purpose of heating.

そして、フィルタ５及び選択還元型ＮＯｘ触媒６が活性化した後は、当該活性状態が維持されていることを条件に、酸化触媒４が一部非活性状態になることを許容するようにバーナ３による排気加熱を弱める。これにより、バーナ３による触媒昇温制御に係る燃料消費量を抑えることが可能になる。   After the filter 5 and the selective reduction type NOx catalyst 6 are activated, the burner 3 is allowed to allow the oxidation catalyst 4 to be partially deactivated on the condition that the activated state is maintained. Reduce the exhaust heating by. Thereby, it becomes possible to suppress the fuel consumption related to the catalyst temperature increase control by the burner 3.

従って、触媒昇温制御における燃費の悪化を抑制することが可能になる。酸化触媒４の下流端の領域Ｘ３が非活性状態となった場合には、バーナ３による触媒昇温制御の強度を所定の強度に戻す（図３の実線Ａ）。   Accordingly, it is possible to suppress deterioration of fuel consumption in the catalyst temperature increase control. When the downstream end region X3 of the oxidation catalyst 4 becomes inactive, the intensity of the catalyst temperature increase control by the burner 3 is returned to a predetermined intensity (solid line A in FIG. 3).

また、フィルタ５や選択還元型ＮＯｘ触媒６の温度が活性温度より低くなった場合も触媒昇温制御の強度を所定の強度に戻す。   Further, when the temperature of the filter 5 or the selective reduction type NOx catalyst 6 becomes lower than the activation temperature, the strength of the catalyst temperature increase control is returned to a predetermined strength.

以上説明したように、本実施例の排気浄化システムでは、フィルタ５及び選択還元型ＮＯｘ触媒６が活性化状態である場合に、酸化触媒４の一部領域が非活性状態をも含む低温状態となることが許容される。この場合、酸化触媒４の非活性領域においてはＨＣやＣＯの酸化作用が得られないことになる。   As described above, in the exhaust purification system of the present embodiment, when the filter 5 and the selective reduction type NOx catalyst 6 are in an activated state, a partial region of the oxidation catalyst 4 includes a low temperature state including an inactive state. It is allowed to be. In this case, the oxidizing action of HC or CO cannot be obtained in the inactive region of the oxidation catalyst 4.

しかしながら、本実施例の排気浄化システムでは、バーナ３を備えており、バーナ３によって排気加熱を行うとＨＣやＣＯのエミッションが著しく低減することがわかっている。従って、酸化触媒４の一部領域が非活性状態となることを許容したとしても、それによって排気浄化システム全体としてＨＣやＣＯのエミッションが悪化することは抑制できる。   However, it has been found that the exhaust purification system of the present embodiment includes the burner 3, and when the exhaust gas is heated by the burner 3, the emission of HC and CO is remarkably reduced. Therefore, even if a partial region of the oxidation catalyst 4 is allowed to become inactive, it is possible to suppress deterioration of HC and CO emissions as a whole of the exhaust purification system.

ここで、酸化触媒４が低温状態の場合には、酸化触媒４に排気中のＮＯｘが吸着する。酸化触媒４に吸着したＮＯｘは酸化触媒４の温度が上昇した際に酸化触媒４から脱離する。酸化触媒４から脱離したＮＯｘはフィルタ５の酸化触媒においてＮＯからＮＯ２を生成する酸化反応に関与する。 Here, when the oxidation catalyst 4 is in a low temperature state, NOx in the exhaust is adsorbed on the oxidation catalyst 4. The NOx adsorbed on the oxidation catalyst 4 is desorbed from the oxidation catalyst 4 when the temperature of the oxidation catalyst 4 rises. NOx desorbed from the oxidation catalyst 4 is involved in an oxidation reaction for generating NO 2 from NO in the oxidation catalyst of the filter 5.

これにより、選択還元型ＮＯｘ触媒６におけるアンモニアを還元剤とするＮＯｘの還元浄化反応に同程度の量のＮＯとＮＯ２が関与するようにできるので、選択還元型ＮＯｘ触媒６の高いＮＯｘ浄化率を達成できる。 As a result, since the same amount of NO and NO 2 can be involved in the NOx reduction purification reaction using ammonia as the reducing agent in the selective reduction type NOx catalyst 6, the NOx purification rate of the selective reduction type NOx catalyst 6 is high. Can be achieved.

なお、選択還元型ＮＯｘ触媒６の特性や排気浄化システムの構成によっては、選択還元型ＮＯｘ触媒６によるＮＯｘ浄化率が選択還元型ＮＯｘ触媒６に流入するＮＯ２の量に対して感度が低い場合がある。そのような場合は、フィルタ５の酸化触媒が酸化触媒４と同様一部非活性状態となることを許容しても、選択還元型ＮＯｘ触媒６の高いＮＯｘ浄化率が得られる場合もある。 Depending on the characteristics of the selective reduction type NOx catalyst 6 and the configuration of the exhaust purification system, the NOx purification rate by the selective reduction type NOx catalyst 6 is low in sensitivity to the amount of NO 2 flowing into the selective reduction type NOx catalyst 6. There is. In such a case, even if the oxidation catalyst of the filter 5 is allowed to be partially inactivated like the oxidation catalyst 4, a high NOx purification rate of the selective reduction type NOx catalyst 6 may be obtained.

すなわち、このような場合には、酸化触媒４だけでなく、フィルタ５もその一部領域が非活性状態となることを許容することができる。この場合、酸化触媒４、フィルタ５及び選択還元型ＮＯｘ触媒６の温度制御は、図５の破線Ｃに示すようになる。図５は、フィルタ５を酸化触媒４と同様３つの領域に分割し、最下流側の領域が活性温度以上であることを条件にそれより上流側の領域が非活性状態となることを許容した場合に可能な温度制御を例示的に示している。   That is, in such a case, not only the oxidation catalyst 4 but also the filter 5 can be allowed to be partially deactivated. In this case, the temperature control of the oxidation catalyst 4, the filter 5, and the selective reduction type NOx catalyst 6 is as shown by a broken line C in FIG. FIG. 5 divides the filter 5 into three regions similar to the oxidation catalyst 4 and allows the region on the upstream side to be in an inactive state on condition that the region on the most downstream side is equal to or higher than the activation temperature. The temperature control possible in the case is shown by way of example.

これにより、バーナ３による排気加熱の強度を所定の強度より弱い強度に調節可能な期間を長く確保できるようになる。従って、より一層の燃費悪化抑制効果が得られる。   As a result, it is possible to ensure a long period during which the intensity of the exhaust heating by the burner 3 can be adjusted to be weaker than a predetermined intensity. Therefore, a further effect of suppressing fuel consumption deterioration can be obtained.

図６は以上説明した本実施例の排気浄化システムによる触媒昇温制御を行った場合の、バーナ３による排気加熱の強度、選択還元型ＮＯｘ触媒６の温度、酸化触媒４の温度、酸化触媒４におけるＮＯｘ吸着量の時間変化の一例を示す図である。なお、図６は概念図であり、時間や温度のスケールは実際に観測されるものとは異なる場合がある。   FIG. 6 shows the intensity of exhaust heating by the burner 3, the temperature of the selective reduction NOx catalyst 6, the temperature of the oxidation catalyst 4, and the oxidation catalyst 4 when the catalyst temperature raising control is performed by the exhaust purification system of the present embodiment described above. It is a figure which shows an example of the time change of the NOx adsorption amount in. FIG. 6 is a conceptual diagram, and the time and temperature scales may differ from those actually observed.

ここでは簡単のためフィルタ５の温度変化については省略した。図６（Ａ）に示すように、選択還元型ＮＯｘ触媒６の温度が活性温度より低いことによりバーナ３による所定の強度（強い強度）による触媒昇温制御の実行が要求されると、図３の実線Ａで示すような強い強度でバーナ３による排気加熱が開始される。   Here, the temperature change of the filter 5 is omitted for simplicity. As shown in FIG. 6 (A), when the temperature of the selective reduction type NOx catalyst 6 is lower than the activation temperature, the execution of the catalyst temperature increase control with a predetermined strength (strong strength) by the burner 3 is required. Exhaust heating by the burner 3 is started with a strong strength as indicated by the solid line A.

バーナ３による強い強度の排気加熱の実施により、図６（Ｃ）に示すように酸化触媒４の温度が上昇し始める。図６（Ｃ）において、酸化触媒４の各領域Ｘ１，Ｘ２及びＸ３における温度変化を別々の曲線で表している。   Due to the strong exhaust gas heating by the burner 3, the temperature of the oxidation catalyst 4 starts to rise as shown in FIG. In FIG. 6C, temperature changes in the respective regions X1, X2, and X3 of the oxidation catalyst 4 are represented by separate curves.

図６（Ｃ）に示すように、最上流側の領域Ｘ１が最も温度上昇しやすく、下流側の領域ほど温度上昇の速度が遅くなる。図６（Ｄ）に示すように、酸化触媒４に非活性状態の領域が存在する場合、酸化触媒４におけるＮＯｘの吸着量が増加する。   As shown in FIG. 6C, the most upstream region X1 is most likely to rise in temperature, and the downstream region has a slower temperature increase rate. As shown in FIG. 6D, when the oxidation catalyst 4 includes a non-active region, the NOx adsorption amount in the oxidation catalyst 4 increases.

酸化触媒４における活性温度以上の領域が増加すると、酸化触媒４に吸着していたＮＯｘの脱離が促進されたＮＯｘの吸着量が減少する。   When the region above the activation temperature in the oxidation catalyst 4 increases, the NOx adsorption amount in which the desorption of NOx adsorbed on the oxidation catalyst 4 is promoted decreases.

時刻ｔ１において選択還元型ＮＯｘ触媒６の温度が活性温度以上になる。この時、バーナ３による強い強度の排気加熱により、酸化触媒４の温度は全領域とも活性温度よりかなり高い温度になっている。ここで、選択還元型ＮＯｘ触媒６の温度が活性温度以上かつ酸化触媒４の少なくとも下流端の領域Ｘ３の温度が活性温度以上という条件が満たされるので、バーナ３による排気加熱の強度が弱められる。   At time t1, the temperature of the selective reduction NOx catalyst 6 becomes equal to or higher than the activation temperature. At this time, due to the strong exhaust gas heating by the burner 3, the temperature of the oxidation catalyst 4 is considerably higher than the activation temperature in all regions. Here, since the condition that the temperature of the selective reduction type NOx catalyst 6 is equal to or higher than the activation temperature and the temperature of at least the downstream end region X3 of the oxidation catalyst 4 is equal to or higher than the activation temperature is satisfied, the intensity of exhaust heating by the burner 3 is weakened.

これにより、酸化触媒４の各領域の温度が低下し始めるが、図６（Ｃ）に示すように、上流側の領域Ｘ１が最も早く温度低下し、下流側の領域ほど温度低下は遅い。そのため、図６（Ｃ）に示すように、酸化触媒４の上流側領域Ｘ１やＸ２の温度が活性温度より低い温度まで低下しても、下流端の領域Ｘ３の温度が活性温度以上の状態になる。   As a result, the temperature of each region of the oxidation catalyst 4 begins to decrease, but as shown in FIG. 6C, the temperature of the upstream region X1 decreases most quickly, and the temperature decrease is slower in the downstream region. Therefore, as shown in FIG. 6C, even if the temperature of the upstream region X1 or X2 of the oxidation catalyst 4 is lowered to a temperature lower than the activation temperature, the temperature of the downstream region X3 is equal to or higher than the activation temperature. Become.

この時、酸化触媒４の領域Ｘ１やＸ２は非活性状態となっているが、本実施例の制御では図６（Ａ）に示すようにバーナ３の排気加熱の強度が弱に制御されたままとなる。この
時、図６（Ｂ）に示すように、選択還元型ＮＯｘ触媒６の温度上昇は鈍化し、或いは低下する場合もあるが、活性温度より高い状態は保つことができる。 At this time, the regions X1 and X2 of the oxidation catalyst 4 are in an inactive state, but in the control of this embodiment, the intensity of the exhaust gas heating of the burner 3 is controlled to be weak as shown in FIG. It becomes. At this time, as shown in FIG. 6 (B), the temperature increase of the selective reduction type NOx catalyst 6 may slow down or decrease, but the state higher than the activation temperature can be maintained.

これは、バーナ３による排気加熱の強度が弱くされることによる影響が最下流側に配置された選択還元型ＮＯｘ触媒６に現われるのに遅れがあることが一因となっている。また、酸化触媒４の上流側領域Ｘ１やＸ２が非活性状態となることにより、図６（Ｄ）に示すように、酸化触媒４のＮＯｘ吸着量が増加傾向になる。   This is partly because there is a delay in the effect of the weakening of the exhaust heating by the burner 3 appearing in the selective reduction type NOx catalyst 6 arranged on the most downstream side. Further, when the upstream region X1 or X2 of the oxidation catalyst 4 becomes inactive, the NOx adsorption amount of the oxidation catalyst 4 tends to increase as shown in FIG. 6 (D).

時刻ｔ２において酸化触媒４の下流端の領域Ｘ３の温度が活性温度より低くなると、バーナ３による排気加熱の強度を弱くすることが可能な条件が満たされなくなるので、バーナ３による排気加熱の強度が元の強い強度に戻される。   When the temperature of the region X3 at the downstream end of the oxidation catalyst 4 becomes lower than the activation temperature at time t2, the condition that can weaken the exhaust heating intensity by the burner 3 is not satisfied, so that the exhaust heating intensity by the burner 3 is reduced. The original strong strength is restored.

これにより図６（Ｃ）に示すように酸化触媒４の各領域の温度が上昇し始める。温度上昇の速度についても上流側領域ほど早い。また、排気加熱の強度が強に制御されることにより、選択還元型ＮＯｘ触媒６の温度は若干上昇傾向になる。   As a result, the temperature of each region of the oxidation catalyst 4 begins to rise as shown in FIG. The rate of temperature rise is also faster in the upstream region. In addition, the temperature of the selective reduction type NOx catalyst 6 tends to slightly increase by controlling the exhaust heating intensity strongly.

また、酸化触媒４の温度が上流側領域から徐々に上昇して活性温度以上になっていくため、図６（Ｄ）に示すように酸化触媒４のＮＯｘ吸着量が増加傾向から減少傾向へ変化する。   Further, since the temperature of the oxidation catalyst 4 gradually rises from the upstream region to the activation temperature or more, the NOx adsorption amount of the oxidation catalyst 4 changes from an increasing tendency to a decreasing tendency as shown in FIG. 6 (D). To do.

時刻ｔ３において酸化触媒４の下流端の領域Ｘ３の温度が活性温度以上になった時に、図６（Ｂ）に示すように選択還元型ＮＯｘ触媒６の温度も活性温度以上であるので、バーナ３による排気加熱の強度を弱めることが可能な条件が満たされ、バーナ３による排気加熱の強度が弱に制御される。   When the temperature of the region X3 at the downstream end of the oxidation catalyst 4 becomes equal to or higher than the activation temperature at time t3, the temperature of the selective reduction NOx catalyst 6 is also equal to or higher than the activation temperature as shown in FIG. The condition for reducing the intensity of the exhaust heating by is satisfied, and the intensity of the exhaust heating by the burner 3 is controlled to be weak.

これにより、上述の場合と同様酸化触媒４の各領域の温度が低下し始める。ここで、このバーナ３にほる排気加熱の強度が弱められた後、時刻ｔ４において図６（Ｂ）に示すように選択還元型ＮＯｘ触媒６の温度が活性温度より低くなったとする。   Thereby, the temperature of each area | region of the oxidation catalyst 4 begins to fall similarly to the above-mentioned case. Here, it is assumed that the temperature of the selective reduction type NOx catalyst 6 becomes lower than the activation temperature at time t4 as shown in FIG. 6B after the intensity of the exhaust heating along the burner 3 is weakened.

この時、図６（Ｃ）に示すように酸化触媒４の下流端の領域Ｘ３の温度は活性温度以上であるとする。この場合、バーナ３による排気加熱の強度を弱めることが可能な条件の内、酸化触媒４の下流端領域Ｘ３の温度に関する条件は満たすものの、選択還元型ＮＯｘ触媒の温度に関する条件が満たされなくなるので、図６（Ａ）に示すようにバーナ３による排気加熱の強度を弱くする制御が停止され、元の強い強度での排気加熱が行われる。   At this time, as shown in FIG. 6C, it is assumed that the temperature in the region X3 at the downstream end of the oxidation catalyst 4 is equal to or higher than the activation temperature. In this case, among the conditions that can reduce the intensity of the exhaust gas heating by the burner 3, the condition related to the temperature of the downstream end region X3 of the oxidation catalyst 4 is satisfied, but the condition related to the temperature of the selective reduction type NOx catalyst is not satisfied. As shown in FIG. 6A, the control for reducing the intensity of the exhaust heating by the burner 3 is stopped, and the exhaust heating with the original strong intensity is performed.

これにより酸化触媒４の各領域の温度が上昇に転じるとともに、少し遅れて選択還元型ＮＯｘ触媒６の温度も上昇に転じる。そして、時刻ｔ５において選択還元型ＮＯｘ触媒６の温度が活性温度以上になったとする。これによりバーナ３による排気加熱の強度を弱めることが可能な条件が成立し、図６（Ａ）に示すように排気加熱の強度を弱くする制御が開始される。   As a result, the temperature of each region of the oxidation catalyst 4 starts to rise, and the temperature of the selective reduction type NOx catalyst 6 also starts to rise with a slight delay. Then, it is assumed that the temperature of the selective reduction NOx catalyst 6 becomes equal to or higher than the activation temperature at time t5. As a result, a condition capable of reducing the intensity of exhaust heating by the burner 3 is established, and control for reducing the intensity of exhaust heating is started as shown in FIG.

図７は、本実施例の排気浄化システムにおける触媒昇温制御を表すフローチャートである。図７のフローチャートで表される処理はＥＣＵ１３によって定期的に実行される。   FIG. 7 is a flowchart showing the catalyst temperature increase control in the exhaust purification system of the present embodiment. The process represented by the flowchart of FIG. 7 is periodically executed by the ECU 13.

ステップＳ１０１において、ＥＣＵ１３は触媒昇温制御の実行要否を判定する。ここでは、排気温度センサ９による検出値に基づいて取得されるフィルタ５の温度がフィルタ５の活性温度より低いか、又は排気温度センサ１０による検出値に基づいて取得される選択還元型ＮＯｘ触媒６の温度が選択還元型ＮＯｘ触媒６の活性下限温度より低い場合に、触媒昇温制御の実行が必要と判定する。   In step S101, the ECU 13 determines whether or not the catalyst temperature increase control is necessary. Here, the selective reduction type NOx catalyst 6 obtained based on whether the temperature of the filter 5 acquired based on the detection value by the exhaust temperature sensor 9 is lower than the activation temperature of the filter 5 or based on the detection value by the exhaust temperature sensor 10. Is determined to be necessary to execute the catalyst temperature increase control.

ここで、選択還元型ＮＯｘ触媒は触媒温度が所定の温度範囲内の温度である場合に活性化し、触媒温度がその温度範囲より低い場合及び高い場合は非活性となる。   Here, the selective reduction type NOx catalyst is activated when the catalyst temperature is within a predetermined temperature range, and deactivated when the catalyst temperature is lower or higher than the temperature range.

なお、「活性化」とは、選択還元型ＮＯｘ触媒が排気中のＮＯｘに対して所望の浄化能力を発揮し、所望のＮＯｘ浄化率が得られる状態を意味する。また、「非活性」とは、選択還元型ＮＯｘ触媒が排気中のＮＯｘに対して所望の浄化能力を発揮することができず、所望のＮＯｘ浄化率が得られない状態を意味する。   “Activation” means a state in which the selective reduction type NOx catalyst exhibits a desired purification capacity for NOx in the exhaust gas and a desired NOx purification rate is obtained. Further, “inactive” means a state in which the selective reduction type NOx catalyst cannot exhibit a desired purification capacity for NOx in exhaust gas and a desired NOx purification rate cannot be obtained.

「活性下限温度」とは、選択還元型ＮＯｘ触媒が所望のＮＯｘ浄化率の排気浄化能力を発揮することが可能な温度範囲の下限値である。「所望のＮＯｘ浄化率」は、エミッションの規制値などを考慮して予め設定される値である。フィルタ５の活性温度とは、フィルタ５の酸化触媒の活性温度である。   “Activity lower limit temperature” is a lower limit value of a temperature range in which the selective reduction type NOx catalyst can exhibit an exhaust purification ability with a desired NOx purification rate. The “desired NOx purification rate” is a value set in advance in consideration of emission regulation values and the like. The activation temperature of the filter 5 is the activation temperature of the oxidation catalyst of the filter 5.

ステップＳ１０１において触媒昇温制御の実行が必要と判定した場合、ＥＣＵ１３はステップＳ１０２に進む。ステップＳ１０１において触媒昇温制御の実行が不要と判定した場合、ＥＣＵ１３はこのフローチャートの処理を一旦抜ける。   If it is determined in step S101 that the catalyst temperature increase control needs to be executed, the ECU 13 proceeds to step S102. When it is determined in step S101 that it is not necessary to perform the catalyst temperature increase control, the ECU 13 once exits the process of this flowchart.

ステップＳ１０２において、ＥＣＵ１３は触媒昇温制御を実行する。ここでは、触媒昇温制御として、バーナ３による排気加熱を実行し、その強度を強に制御する。これにより酸化触媒４、フィルタ５及び選択還元型ＮＯｘ触媒６の全てについて昇温が開始される。   In step S102, the ECU 13 executes catalyst temperature increase control. Here, exhaust gas heating by the burner 3 is executed as the catalyst temperature increase control, and the intensity thereof is controlled to be strong. As a result, the temperature rise is started for all of the oxidation catalyst 4, the filter 5, and the selective reduction type NOx catalyst 6.

ステップＳ１０３において、ＥＣＵ１３はフィルタ５及び選択還元型ＮＯｘ触媒６の温度が各々の活性温度以上になったか否かを判定する。フィルタ５の温度がフィルタ５の活性温度より低いか、選択還元型ＮＯｘ触媒６の温度が選択還元型ＮＯｘ触媒６の活性下限温度より低いか、のいずれかの場合、ＥＣＵ１３はステップＳ１０２に戻り、強い強度に調節されたバーナ３による触媒昇温制御を継続する。   In step S103, the ECU 13 determines whether or not the temperatures of the filter 5 and the selective reduction type NOx catalyst 6 are equal to or higher than the respective activation temperatures. When the temperature of the filter 5 is lower than the activation temperature of the filter 5 or the temperature of the selective reduction type NOx catalyst 6 is lower than the lower limit activation temperature of the selective reduction type NOx catalyst 6, the ECU 13 returns to step S102, The catalyst temperature increase control by the burner 3 adjusted to a strong strength is continued.

一方、ステップＳ１０３においてフィルタ５の温度がフィルタ５の活性温度以上かつ選択還元型ＮＯｘ触媒６の温度が選択還元型ＮＯｘ触媒６の活性下限温度以上であると判定した場合、ＥＣＵ１３はステップＳ１０４に進む。   On the other hand, if it is determined in step S103 that the temperature of the filter 5 is equal to or higher than the activation temperature of the filter 5 and the temperature of the selective reduction NOx catalyst 6 is equal to or higher than the activation lower limit temperature of the selective reduction NOx catalyst 6, the ECU 13 proceeds to step S104. .

ステップＳ１０４において、ＥＣＵ１３は酸化触媒４の少なくとも下流端の領域Ｘ３の温度が酸化触媒４の活性温度以上であるか否かを判定する。ここで、酸化触媒４の各領域Ｘ１，Ｘ２及びＸ３の温度は、エンジン１の運転状態や排気温度センサ８による検出値などに基づいて演算して取得する。   In step S <b> 104, the ECU 13 determines whether or not the temperature of at least the downstream end region X <b> 3 of the oxidation catalyst 4 is equal to or higher than the activation temperature of the oxidation catalyst 4. Here, the temperatures of the respective regions X1, X2, and X3 of the oxidation catalyst 4 are obtained by calculation based on the operating state of the engine 1, the detection value by the exhaust temperature sensor 8, and the like.

また、酸化触媒４の各領域の温度をセンサにより直接検出することも勿論可能である。ここでは、酸化触媒４の下流端の領域Ｘ３の温度に基づいて判定を行うので、少なくとも領域Ｘ３の温度だけが取得できれば十分である。   Of course, the temperature of each region of the oxidation catalyst 4 can be directly detected by a sensor. Here, since the determination is performed based on the temperature of the region X3 at the downstream end of the oxidation catalyst 4, it is sufficient if only the temperature of the region X3 can be acquired.

本実施例において酸化触媒の領域Ｘ３の温度を取得する処理を実行するＥＣＵ１３が本発明における「温度分布検出手段」として機能している。酸化触媒４の少なくとも下流端の領域Ｘ３の温度が活性温度以上であると判定した場合、ＥＣＵ１３はステップＳ１０５に進む。一方、酸化触媒４の下流端の領域Ｘ３の温度が活性温度より低い場合、ＥＣＵ１３はステップＳ１０２に戻り、強い強度に調節した触媒昇温制御を実行する。   In this embodiment, the ECU 13 that executes the process of acquiring the temperature of the region X3 of the oxidation catalyst functions as the “temperature distribution detecting means” in the present invention. When it is determined that the temperature of at least the downstream end region X3 of the oxidation catalyst 4 is equal to or higher than the activation temperature, the ECU 13 proceeds to step S105. On the other hand, when the temperature of the region X3 at the downstream end of the oxidation catalyst 4 is lower than the activation temperature, the ECU 13 returns to step S102 and executes catalyst temperature increase control adjusted to a strong strength.

ステップＳ１０５において、ＥＣＵ１３は選択還元型ＮＯｘ触媒６の温度が活性上限温度以下であるか否かを判定する。選択還元型ＮＯｘ触媒は、触媒温度が活性下限温度以上であれば触媒活性自体は得られるものの、触媒温度が高すぎるとアンモニアが吸着しにくくなるためにＮＯｘの還元反応が起こりにくくなり、結果として所望のＮＯｘ浄化率が得
られなくなる。 In step S105, the ECU 13 determines whether or not the temperature of the selective reduction type NOx catalyst 6 is equal to or lower than the activation upper limit temperature. The selective reduction type NOx catalyst can obtain the catalytic activity itself if the catalyst temperature is equal to or higher than the lower limit temperature of the activity, but if the catalyst temperature is too high, it is difficult for the NOx reduction reaction to occur because ammonia is difficult to adsorb. A desired NOx purification rate cannot be obtained.

「活性上限温度」とは、選択還元型ＮＯｘ触媒が所望のＮＯｘ浄化率の排気浄化能力を発揮することが可能な温度範囲の上限値である。この意味で、上記の実施例の説明において単に「選択還元型ＮＯｘ触媒の活性温度以上」といった場合、それは「選択還元型ＮＯｘ触媒の活性上限温度以上」ではなく「選択還元型ＮＯｘ触媒の活性下限温度以上」を意味するものと捉えることができる。   The “activity upper limit temperature” is an upper limit value of a temperature range in which the selective reduction type NOx catalyst can exhibit an exhaust purification ability with a desired NOx purification rate. In this sense, in the description of the above embodiment, when the term “above the active temperature of the selective reduction NOx catalyst” is used, it is not “above the active upper limit temperature of the selective reduction NOx catalyst” but “the lower limit of activity of the selective reduction NOx catalyst”. It can be understood as meaning “over temperature”.

ステップＳ１０５において、選択還元型ＮＯｘ触媒６の温度が活性上限温度以下と判定した場合、ＥＣＵ１３はステップＳ１０６に進み、バーナ３による触媒昇温制御の強度を弱に調節する。   If it is determined in step S105 that the temperature of the selective reduction NOx catalyst 6 is equal to or lower than the activation upper limit temperature, the ECU 13 proceeds to step S106 and adjusts the strength of the catalyst temperature increase control by the burner 3 to be weak.

一方、ステップＳ１０５において、選択還元型ＮＯｘ触媒６の温度が活性上限温度より高いと判定した場合、ＥＣＵ１３はステップＳ１０７に進み、バーナ３による触媒昇温制御を停止する。   On the other hand, if it is determined in step S105 that the temperature of the selective reduction NOx catalyst 6 is higher than the activation upper limit temperature, the ECU 13 proceeds to step S107 and stops the catalyst temperature increase control by the burner 3.

ステップＳ１０６においてバーナ３による触媒昇温制御の強度を弱くした後、ＥＣＵ１３はステップＳ１０３に戻り、フィルタ５の温度が活性温度以上かつ選択還元型ＮＯｘ触媒６の温度が活性下限温度以上であるかの判定を行う。以降の処理は上述した通りである。   After reducing the strength of the catalyst temperature increase control by the burner 3 in step S106, the ECU 13 returns to step S103 to check whether the temperature of the filter 5 is equal to or higher than the activation temperature and the temperature of the selective reduction type NOx catalyst 6 is equal to or higher than the activation lower limit temperature. Make a decision. Subsequent processing is as described above.

バーナ３による排気加熱の強度、すなわち燃料噴射弁１４による燃料噴射量を調節するＥＣＵ１３が本発明における「昇温強度調節手段」として機能している。上記のフローチャートの処理を実行するＥＣＵ１３が本発明における「制御手段」として機能している。   The ECU 13 that adjusts the exhaust heating intensity by the burner 3, that is, the fuel injection amount by the fuel injection valve 14, functions as the "temperature increase intensity adjusting means" in the present invention. The ECU 13 that executes the processing of the above flowchart functions as the “control unit” in the present invention.

なお、本実施例では、バーナ３による排気加熱の強度を所定の強い強度と弱い強度との２段階のいずれかに切り替える例を説明したが、２段階より多い設定値を切り替えるようにしても良いし、酸化触媒４の下流端の領域Ｘ３の温度、フィルタ５の温度、選択還元型ＮＯｘ触媒６の温度などに応じて演算される可変値に設定することもできる。   In the present embodiment, an example in which the intensity of exhaust heating by the burner 3 is switched to one of two levels of a predetermined strong intensity and a weak intensity has been described, but a setting value greater than two stages may be switched. However, it may be set to a variable value calculated according to the temperature of the region X3 at the downstream end of the oxidation catalyst 4, the temperature of the filter 5, the temperature of the selective reduction type NOx catalyst 6, and the like.

要は、フィルタ５及び選択還元型ＮＯｘ触媒６が活性状態であり、かつ、酸化触媒４の少なくとも下流端の領域Ｘ３が活性状態であるという条件を満たす場合には、それ以外の場合と比較してバーナ３による排気加熱の強度が弱くなるように制御されるのであれば、どのような制御態様であっても、本実施例の排気浄化システムと同様に燃費悪化抑制の効果が得られる。   In short, when the condition that the filter 5 and the selective reduction type NOx catalyst 6 are in the active state and at least the region X3 at the downstream end of the oxidation catalyst 4 is in the active state is compared with the other cases. As long as it is controlled so that the intensity of the exhaust heating by the burner 3 is weakened, the effect of suppressing the deterioration of fuel consumption can be obtained in any control manner as in the exhaust purification system of the present embodiment.

また、本実施例では酸化触媒４の温度を３つの領域の温度に分けて下流端の領域の温度に応じて触媒昇温制御の強度を制御する例を説明したが、領域分割数は２つでも良いし、３つより多くても良い。   In the present embodiment, the temperature of the oxidation catalyst 4 is divided into three regions, and the intensity of the catalyst temperature increase control is controlled according to the temperature of the downstream region. However, the number of region divisions is two. But it can be more than three.

２つに分けた場合は下流側の領域の温度に応じて、４つ以上の領域に分けた場合は下流側の１又は複数の領域の温度に応じて、バーナ３による触媒昇温制御の強度を制御することができる。   When divided into two, depending on the temperature of the downstream region, and when divided into four or more regions, the strength of the catalyst temperature increase control by the burner 3 according to the temperature of one or more downstream regions Can be controlled.

また、上述したように、酸化触媒４の温度が活性温度より低くなると、酸化触媒４にＮＯｘが吸着する。これにより尿素添加弁７による尿素の供給を行わなくてもＮＯｘの排出が抑制されることになるが、酸化触媒４におけるＮＯｘの吸着量には上限があり、吸着量が所定の飽和量に達すると、酸化触媒４の温度が活性温度より低くてもＮＯｘが吸着しなくなる。   Further, as described above, when the temperature of the oxidation catalyst 4 becomes lower than the activation temperature, NOx is adsorbed on the oxidation catalyst 4. As a result, NOx emission is suppressed without supplying urea by the urea addition valve 7, but the NOx adsorption amount in the oxidation catalyst 4 has an upper limit, and the adsorption amount reaches a predetermined saturation amount. Then, NOx is not adsorbed even if the temperature of the oxidation catalyst 4 is lower than the activation temperature.

この場合、酸化触媒４を昇温させてＮＯｘの離脱を促進させるとともに、尿素添加弁７による尿素の供給を行って選択還元型ＮＯｘ触媒６によるＮＯｘの還元浄化が行われるようにするのが好ましい。   In this case, it is preferable to raise the temperature of the oxidation catalyst 4 to promote the separation of NOx and to supply the urea by the urea addition valve 7 so that the NOx reduction purification by the selective reduction type NOx catalyst 6 is performed. .

図８は、上記説明した本実施例の触媒昇温制御において、酸化触媒４におけるＮＯｘの吸着量を考慮した場合の処理手順を表すフローチャートである。図８のフローチャートにおいて、図７で説明した処理と同一内容の処理を行うステップには図７のフローチャートと同じ番号を付し、説明を割愛する。   FIG. 8 is a flowchart showing a processing procedure when the NOx adsorption amount in the oxidation catalyst 4 is considered in the catalyst temperature increase control of the present embodiment described above. In the flowchart of FIG. 8, steps that perform the same processing as the processing described in FIG. 7 are assigned the same numbers as in the flowchart of FIG. 7, and descriptions thereof are omitted.

図８のフローチャートでは、ステップＳ１０３及びステップＳ１０４において肯定判定された場合、すなわち、バーナ３による触媒昇温制御の強度を弱めることが可能な条件が成立した場合、更に、ステップＳ２０１において酸化触媒４におけるＮＯｘ吸着量が飽和吸着量に達していないか確認する。ＮＯｘ吸着量が飽和吸着量に達している場合には、バーナ３による触媒昇温制御の強度を弱めることはせず、酸化触媒４に吸着するＮＯｘを脱離させるべく、ステップＳ１０２に戻って強い強度での触媒昇温制御を実行する。   In the flowchart of FIG. 8, when an affirmative determination is made in step S103 and step S104, that is, when a condition that can weaken the strength of the catalyst temperature increase control by the burner 3 is satisfied, the oxidation catalyst 4 in step S201 is further satisfied. Check if the NOx adsorption amount has reached the saturated adsorption amount. When the NOx adsorption amount reaches the saturated adsorption amount, the strength of the catalyst temperature increase control by the burner 3 is not weakened, and the process returns to step S102 and strong in order to desorb NOx adsorbed on the oxidation catalyst 4. The catalyst temperature rise control with the strength is executed.

一方、酸化触媒４におけるＮＯｘ吸着量が飽和吸着量に達していない場合には、バーナ３による触媒昇温制御の強度を弱めることが可能と判断する。図７のフローチャートでは、この次に選択還元型ＮＯｘ触媒６の温度が活性上限温度を超えていないか確認する処理を行う例を説明したが、ここでは、代わりにアンモニアスリップが発生する可能性があるか否かを確認する処理を行う例を説明する。   On the other hand, when the NOx adsorption amount in the oxidation catalyst 4 does not reach the saturated adsorption amount, it is determined that the strength of the catalyst temperature increase control by the burner 3 can be weakened. In the flowchart of FIG. 7, the example in which the process for confirming whether the temperature of the selective reduction type NOx catalyst 6 does not exceed the activation upper limit temperature has been described next, but here, ammonia slip may occur instead. An example in which processing for confirming whether or not there is performed will be described.

すなわち、ステップＳ２０１で酸化触媒４におけるＮＯｘ吸着量が飽和吸着量より少ないと判定した場合、ＥＣＵ１３はステップＳ２０２に進み、選択還元型ＮＯｘ触媒６においてアンモニアスリップが発生する可能性があるか否かを判定する。ここでは、選択還元型ＮＯｘ触媒６の触媒温度と選択還元型ＮＯｘ触媒６におけるアンモニア吸着量とに基づいてアンモニアスリップの発生可能性（アンモニアスリップの発生条件の成立有無）を判断する。   That is, if it is determined in step S201 that the NOx adsorption amount in the oxidation catalyst 4 is smaller than the saturated adsorption amount, the ECU 13 proceeds to step S202 and determines whether or not ammonia slip may occur in the selective reduction type NOx catalyst 6. judge. Here, the possibility of occurrence of ammonia slip (whether or not the condition for generating ammonia slip is satisfied) is determined based on the catalyst temperature of the selective reduction type NOx catalyst 6 and the ammonia adsorption amount in the selective reduction type NOx catalyst 6.

選択還元型ＮＯｘ触媒６に吸着可能なアンモニアの量は選択還元型ＮＯｘ触媒６の温度に依存する。図９に選択還元型ＮＯｘ触媒の温度と吸着可能なアンモニアの量との関係を示す。図９に示すように、選択還元型ＮＯｘ触媒６の温度が高くなるほど、吸着可能なアンモニアの量は少なくなる。   The amount of ammonia that can be adsorbed on the selective reduction type NOx catalyst 6 depends on the temperature of the selective reduction type NOx catalyst 6. FIG. 9 shows the relationship between the temperature of the selective reduction NOx catalyst and the amount of ammonia that can be adsorbed. As shown in FIG. 9, the higher the temperature of the selective reduction NOx catalyst 6, the smaller the amount of ammonia that can be adsorbed.

この触媒温度と吸着可能なアンモニアの量との関係はマップとしてＥＣＵ１３に記憶しておくことができる。ＥＣＵ１３は、この触媒温度と吸着可能なアンモニアの量との関係に基づいて、現状よりも選択還元型ＮＯｘ触媒６の温度が上昇した場合に、選択還元型ＮＯｘ触媒６に吸着しているアンモニアが選択還元型ＮＯｘ触媒６より下流側の排気通路２に流出する可能性があるか否かを判定する。   The relationship between the catalyst temperature and the amount of ammonia that can be adsorbed can be stored in the ECU 13 as a map. Based on the relationship between the catalyst temperature and the amount of ammonia that can be adsorbed, the ECU 13 determines that the ammonia adsorbed on the selective reduction type NOx catalyst 6 is increased when the temperature of the selective reduction type NOx catalyst 6 rises from the current level. It is determined whether or not there is a possibility of flowing out into the exhaust passage 2 downstream of the selective reduction type NOx catalyst 6.

現状で選択還元型ＮＯｘ触媒６に吸着しているアンモニアの量は、ＮＯｘセンサ１１により検出される流入ＮＯｘ量、ＮＯｘセンサ１２により検出される流出ＮＯｘ量、尿素添加弁７により添加される尿素の量、エンジン１の運転状態、選択還元型ＮＯｘ触媒６の温度などに基づいて推定する。   Currently, the amount of ammonia adsorbed on the selective reduction type NOx catalyst 6 includes the inflow NOx amount detected by the NOx sensor 11, the outflow NOx amount detected by the NOx sensor 12, and the urea added by the urea addition valve 7. It is estimated based on the amount, the operating state of the engine 1, the temperature of the selective reduction type NOx catalyst 6, and the like.

ステップＳ２０１においてアンモニアスリップが発生する可能性があると判定した場合、ＥＣＵ１３はステップＳ１０７に進んでバーナ３による触媒昇温制御を停止する。一方、ステップＳ２０１においてアンモニアスリップが発生する可能性が無いと判定した場合、ＥＣＵ１３はステップＳ１０６に進んでバーナ３による触媒昇温制御の強度を弱める。ステップＳ２０２の処理を行うＥＣＵ１３が本発明における「アンモニアスリップ発生判
定手段」として機能している。 If it is determined in step S201 that ammonia slip may occur, the ECU 13 proceeds to step S107 and stops the catalyst temperature increase control by the burner 3. On the other hand, if it is determined in step S201 that there is no possibility of ammonia slip, the ECU 13 proceeds to step S106 to weaken the strength of the catalyst temperature increase control by the burner 3. The ECU 13 that performs the process of step S202 functions as “ammonia slip occurrence determination means” in the present invention.

図８のフローチャートによれば、フィルタ５及び選択還元型ＮＯｘ触媒６の温度が活性温度以上かつ酸化触媒４の下流端の領域Ｘ３の温度が活性温度以上かつ酸化触媒４のＮＯｘ吸着量が飽和量より少ないという条件が満たされる場合に、触媒昇温制御の強度が弱められる制御（ステップＳ１０５）が継続されることになる。   According to the flowchart of FIG. 8, the temperature of the filter 5 and the selective reduction type NOx catalyst 6 is equal to or higher than the activation temperature, the temperature of the downstream end region X3 of the oxidation catalyst 4 is equal to or greater than the activation temperature, and the NOx adsorption amount of the oxidation catalyst 4 is saturated. When the condition of less is satisfied, the control (step S105) in which the strength of the catalyst temperature increase control is weakened is continued.

酸化触媒４におけるＮＯｘの吸着量は、酸化触媒４に流入するＮＯｘの積算値や酸化触媒４の温度に基づいて演算することができる。この場合、酸化触媒４のＮＯｘ吸着量を演算により取得するＥＣＵ１３が本発明における「ＮＯｘ吸着量検出手段」として機能している。   The adsorption amount of NOx in the oxidation catalyst 4 can be calculated based on the integrated value of NOx flowing into the oxidation catalyst 4 and the temperature of the oxidation catalyst 4. In this case, the ECU 13 that acquires the NOx adsorption amount of the oxidation catalyst 4 by calculation functions as the “NOx adsorption amount detection means” in the present invention.

また、上述の実施例では酸化触媒、フィルタ及び選択還元型ＮＯｘ触媒が直列配置された排気浄化システムを例に説明したが、酸化触媒と選択還元型ＮＯｘ触媒の組み合わせや、その他酸化触媒と活性化のために昇温を要する何らかの排気浄化触媒との組み合わせに適用することができる。例えば、ＮＯｘ浄化触媒は選択還元型ＮＯｘ触媒に限らず、吸蔵還元型ＮＯｘ触媒でも良い。上記各実施例は可能な限り組み合わせて本発明を実施することができる。   In the above-described embodiments, the exhaust purification system in which the oxidation catalyst, the filter, and the selective reduction type NOx catalyst are arranged in series has been described as an example. However, the combination of the oxidation catalyst and the selective reduction type NOx catalyst, and other oxidation catalysts and activation Therefore, the present invention can be applied to a combination with any exhaust purification catalyst that requires a temperature increase. For example, the NOx purification catalyst is not limited to the selective reduction type NOx catalyst, but may be a storage reduction type NOx catalyst. The above embodiments can be combined as much as possible to implement the present invention.

１ エンジン
２ 排気通路
３ バーナ
４ 酸化触媒
５ フィルタ
６ 選択還元型ＮＯｘ触媒
７ 尿素添加弁
８ 排気温度センサ
９ 排気温度センサ
１０ 排気温度センサ
１１ ＮＯｘセンサ
１２ ＮＯｘセンサ
１３ ＥＣＵ
１４ 燃料噴射弁
１５ 点火プラグ
１６ 空気供給通路
１７ バーナ燃焼室
１８ エアポンプ 1 Engine 2 Exhaust passage 3 Burner 4 Oxidation catalyst 5 Filter 6 Selective reduction type NOx catalyst 7 Urea addition valve 8 Exhaust temperature sensor 9 Exhaust temperature sensor 10 Exhaust temperature sensor 11 NOx sensor 12 NOx sensor 13 ECU
14 Fuel injection valve 15 Spark plug 16 Air supply passage 17 Burner combustion chamber 18 Air pump

Claims (9)

内燃機関の排気通路に設けられる酸化触媒と、
前記酸化触媒より下流側の排気通路に設けられる排気浄化触媒と、
前記酸化触媒及び前記排気浄化触媒の温度を上昇させる触媒昇温制御を実行する触媒昇温手段と、
前記酸化触媒の排気の流れ方向の温度分布を検出する温度分布検出手段と、
前記触媒昇温手段による触媒昇温制御の強度を調節する昇温強度調節手段と、
前記排気浄化触媒の温度が所定の活性温度より低い場合は、前記触媒昇温制御の強度を所定の強度に調節し、該所定の強度の触媒昇温制御により前記排気浄化触媒の温度が活性温度以上に上昇した場合は、前記排気浄化触媒の温度が活性温度以上かつ前記温度分布検出手段により検出される温度分布において少なくとも前記酸化触媒の下流端近傍の所定領域の温度が酸化触媒の活性温度以上であれば、前記触媒昇温制御の強度を前記所定の強度よりも弱い強度に調節するように、前記昇温強度調節手段を制御する制御手段と、
を備える内燃機関の排気浄化装置。 An oxidation catalyst provided in the exhaust passage of the internal combustion engine;
An exhaust purification catalyst provided in an exhaust passage downstream of the oxidation catalyst;
Catalyst temperature raising means for performing catalyst temperature raising control for raising the temperature of the oxidation catalyst and the exhaust purification catalyst;
Temperature distribution detecting means for detecting a temperature distribution in the exhaust flow direction of the oxidation catalyst;
A temperature increase intensity adjusting means for adjusting the intensity of the catalyst temperature increase control by the catalyst temperature increase means;
When the temperature of the exhaust purification catalyst is lower than a predetermined activation temperature, the intensity of the catalyst temperature increase control is adjusted to a predetermined intensity, and the temperature of the exhaust purification catalyst is increased to the activation temperature by the catalyst temperature increase control with the predetermined intensity. When the temperature rises above, the temperature of the exhaust purification catalyst is equal to or higher than the activation temperature, and at least the temperature in the predetermined region near the downstream end of the oxidation catalyst is equal to or higher than the activation temperature of the oxidation catalyst in the temperature distribution detected by the temperature distribution detection means. If so, control means for controlling the temperature rise intensity adjusting means so as to adjust the intensity of the catalyst temperature rise control to a weaker intensity than the predetermined intensity,
An exhaust gas purification apparatus for an internal combustion engine. 請求項１において、
前記排気浄化触媒は、排気中のＮＯｘを浄化するＮＯｘ浄化触媒を含み、
前記制御手段は、前記ＮＯｘ浄化触媒の温度がＮＯｘ浄化触媒の活性温度より低い場合は、前記触媒昇温制御の強度を所定の強度に調節し、該所定の強度の触媒昇温制御により前記ＮＯｘ浄化触媒の温度がＮＯｘ浄化触媒の活性温度以上に上昇した場合は、前記ＮＯｘ浄化触媒の温度がＮＯｘ浄化触媒の活性温度以上かつ前記温度分布検出手段により検出される温度分布において少なくとも前記酸化触媒の下流端近傍の所定領域の温度が酸化触媒の活性温度以上であれば、前記触媒昇温制御の強度を前記所定の強度よりも弱い強度に調節するように、前記昇温強度調節手段を制御することを特徴とする内燃機関の排気浄化装置。 In claim 1,
The exhaust purification catalyst includes a NOx purification catalyst that purifies NOx in the exhaust,
When the temperature of the NOx purification catalyst is lower than the activation temperature of the NOx purification catalyst, the control means adjusts the intensity of the catalyst temperature increase control to a predetermined intensity, and performs the NOx purification catalyst temperature increase control with the predetermined intensity. When the temperature of the purification catalyst rises above the activation temperature of the NOx purification catalyst, the temperature of the NOx purification catalyst is equal to or higher than the activation temperature of the NOx purification catalyst and at least in the temperature distribution detected by the temperature distribution detection means. If the temperature of the predetermined region near the downstream end is equal to or higher than the activation temperature of the oxidation catalyst, the temperature increase intensity adjusting means is controlled so that the intensity of the catalyst temperature increase control is adjusted to be weaker than the predetermined intensity. An exhaust emission control device for an internal combustion engine. 請求項２において、
前記排気浄化触媒は、前記ＮＯｘ浄化触媒の上流側に設けられ、排気中の微粒子物質を捕集するとともに酸化触媒を有するフィルタを含み、
前記制御手段は、前記ＮＯｘ浄化触媒の温度がＮＯｘ浄化触媒の活性温度より低いか又は前記フィルタの温度がフィルタの活性温度より低い場合は、前記触媒昇温制御の強度を所定の強度に調節し、該所定の強度の触媒昇温制御により前記フィルタの温度がフィルタの活性温度以上に上昇し且つ前記ＮＯｘ浄化触媒の温度がＮＯｘ浄化触媒の活性温度以上に上昇した場合は、前記フィルタの温度がフィルタの活性温度以上かつ前記ＮＯｘ浄化触媒の温度がＮＯｘ浄化触媒の活性温度以上かつ前記温度分布検出手段により検出される温度分布において少なくとも前記酸化触媒の下流端近傍の所定領域の温度が酸化触媒の活性温度以上であれば、前記触媒昇温制御の強度を前記所定の強度よりも弱い強度に調節するように、前記昇温強度調節手段を制御することを特徴とする内燃機関の排気浄化装置。 In claim 2,
The exhaust purification catalyst includes a filter that is provided on the upstream side of the NOx purification catalyst and collects particulate matter in the exhaust and has an oxidation catalyst.
When the temperature of the NOx purification catalyst is lower than the activation temperature of the NOx purification catalyst or the temperature of the filter is lower than the activation temperature of the filter, the control means adjusts the intensity of the catalyst temperature increase control to a predetermined intensity. When the temperature of the filter rises above the activation temperature of the filter and the temperature of the NOx purification catalyst rises above the activation temperature of the NOx purification catalyst by the catalyst temperature increase control of the predetermined strength, the temperature of the filter is In the temperature distribution above the activation temperature of the filter and the temperature of the NOx purification catalyst is above the activation temperature of the NOx purification catalyst and detected by the temperature distribution detection means, at least the temperature in the predetermined region near the downstream end of the oxidation catalyst is the temperature of the oxidation catalyst. The temperature increase intensity adjusting means adjusts the intensity of the catalyst temperature increase control to an intensity weaker than the predetermined intensity if the activation temperature is higher than the activation temperature. Exhaust purifying apparatus for an internal combustion engine and controlling. 請求項１から３のいずれか１項において、
前記酸化触媒におけるＮＯｘの吸着量を検出するＮＯｘ吸着量検出手段を備え、
前記制御手段は、前記ＮＯｘ吸着量検出手段により検出されるＮＯｘの吸着量が所定量以上になったと判定された場合、前記触媒昇温制御の強度を前記所定の強度に調節するように前記昇温強度調節手段を制御することを特徴とする内燃機関の排気浄化装置。 In any one of Claim 1 to 3,
NOx adsorption amount detection means for detecting the NOx adsorption amount in the oxidation catalyst,
When it is determined that the NOx adsorption amount detected by the NOx adsorption amount detection unit has become equal to or greater than a predetermined amount, the controller is configured to adjust the intensity of the catalyst temperature increase control to the predetermined intensity. An exhaust emission control device for an internal combustion engine, characterized by controlling temperature intensity adjusting means. 請求項１から４のいずれか１項において、
前記排気浄化触媒は、所定の温度範囲において活性化するとともに該温度範囲より温度が高い場合及び低い場合には非活性となる触媒を含み、
前記制御手段は、前記触媒昇温制御の強度を前記所定の強度又は前記所定の強度より弱
い強度に調節するように前記昇温強度調節手段を制御しているときに、前記触媒の温度が前記温度範囲より高くなった場合は、前記触媒昇温制御を停止するよう前記触媒昇温手段を制御することを特徴とする内燃機関の排気浄化装置。 In any one of Claims 1-4,
The exhaust purification catalyst includes a catalyst that is activated in a predetermined temperature range and deactivated when the temperature is higher and lower than the temperature range,
The control means controls the temperature rise intensity adjusting means so as to adjust the intensity of the catalyst temperature rise control to the predetermined intensity or weaker than the predetermined intensity. An exhaust gas purifying apparatus for an internal combustion engine, wherein the catalyst temperature raising means is controlled to stop the catalyst temperature raising control when the temperature is higher than a temperature range. 請求項１から５のいずれか１項において
前記排気浄化触媒は、アンモニアを吸着して排気中のＮＯｘを選択的に還元浄化する選択還元型ＮＯｘ触媒を含み、
前記内燃機関の排気浄化装置は、
前記選択還元型ＮＯｘ触媒の温度及びアンモニア吸着量に基づいて前記選択還元型ＮＯｘ触媒からアンモニアが流出するアンモニアスリップの発生条件が成立するか判定するアンモニアスリップ発生判定手段を更に備え、
前記制御手段は、前記触媒昇温制御の強度を前記所定の強度又は前記所定の強度より弱い強度に調節するように前記昇温強度調節手段を制御しているときに、前記アンモニアスリップ発生判定手段によりアンモニアスリップの発生条件が成立すると判定された場合は、前記触媒昇温制御を停止するよう前記触媒昇温手段を制御することを特徴とする内燃機関の排気浄化装置。 The exhaust purification catalyst according to any one of claims 1 to 5, comprising a selective reduction type NOx catalyst that adsorbs ammonia and selectively reduces and purifies NOx in the exhaust,
The exhaust gas purification device for the internal combustion engine includes:
Ammonia slip generation determination means for determining whether an ammonia slip generation condition in which ammonia flows out of the selective reduction NOx catalyst is satisfied based on the temperature of the selective reduction NOx catalyst and the ammonia adsorption amount;
The control means controls the temperature rise intensity adjusting means so as to adjust the intensity of the catalyst temperature rise control to the predetermined intensity or an intensity weaker than the predetermined intensity. When it is determined that the conditions for generating ammonia slip are satisfied, the catalyst temperature raising means is controlled so as to stop the catalyst temperature raising control. 請求項１から６のいずれか１項において、
前記触媒昇温手段は、燃料を噴射する燃料噴射手段と、該噴射された燃料に着火する着火手段と、を有し、前記酸化触媒より上流の排気の温度を上昇させるバーナであることを特徴とする内燃機関の排気浄化装置。 In any one of Claim 1 to 6,
The catalyst temperature raising means is a burner having fuel injection means for injecting fuel and ignition means for igniting the injected fuel, and for raising the temperature of exhaust gas upstream from the oxidation catalyst. An exhaust purification device for an internal combustion engine. 請求項７において、
前記昇温強度調節手段は、前記燃料噴射手段により噴射される燃料量を調節することにより触媒昇温制御の強度を調節することを特徴とする内燃機関の排気浄化装置。 In claim 7,
The exhaust gas purification apparatus for an internal combustion engine, wherein the temperature increase intensity adjusting means adjusts the intensity of the catalyst temperature increase control by adjusting the amount of fuel injected by the fuel injection means. 請求項１から８のいずれか１項において、
前記温度分布検出手段は、前記酸化触媒を複数の領域に分割した場合の各領域の温度を検出することを特徴とする内燃機関の排気浄化装置。 In any one of Claims 1-8,
The exhaust gas purification apparatus for an internal combustion engine, wherein the temperature distribution detecting means detects the temperature of each region when the oxidation catalyst is divided into a plurality of regions.
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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2014054064A1 (en) * 2012-10-01 2014-04-10 トヨタ自動車株式会社 Exhaust heating device of internal combustion engine, and exhaust heating method
CN104314651A (en) * 2014-08-15 2015-01-28 潍柴动力股份有限公司 Aging correction method and correction device for ternary catalyst
JP2017061878A (en) * 2015-09-24 2017-03-30 株式会社日本自動車部品総合研究所 Exhaust emission control device for internal combustion engine
CN109621721A (en) * 2018-11-30 2019-04-16 无锡市杜克环保科技有限公司 A kind of mobile self-cleaning diesel engine vent gas purification system

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2014054064A1 (en) * 2012-10-01 2014-04-10 トヨタ自動車株式会社 Exhaust heating device of internal combustion engine, and exhaust heating method
CN104314651A (en) * 2014-08-15 2015-01-28 潍柴动力股份有限公司 Aging correction method and correction device for ternary catalyst
JP2017061878A (en) * 2015-09-24 2017-03-30 株式会社日本自動車部品総合研究所 Exhaust emission control device for internal combustion engine
CN109621721A (en) * 2018-11-30 2019-04-16 无锡市杜克环保科技有限公司 A kind of mobile self-cleaning diesel engine vent gas purification system

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