JP2010121478A - Exhaust emission control device and exhaust emission control system for internal combustion engine - Google Patents

Exhaust emission control device and exhaust emission control system for internal combustion engine Download PDF

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JP2010121478A
JP2010121478A JP2008294029A JP2008294029A JP2010121478A JP 2010121478 A JP2010121478 A JP 2010121478A JP 2008294029 A JP2008294029 A JP 2008294029A JP 2008294029 A JP2008294029 A JP 2008294029A JP 2010121478 A JP2010121478 A JP 2010121478A
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internal combustion
combustion engine
exhaust
amount
temperature
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Tatsuya Fujita
達也 藤田
Masatoshi Maruyama
昌利 丸山
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Denso Corp
Soken Inc
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Denso Corp
Nippon Soken Inc
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Priority to JP2008294029A priority Critical patent/JP2010121478A/en
Priority to US12/619,044 priority patent/US20100122525A1/en
Priority to DE102009044546A priority patent/DE102009044546A1/en
Publication of JP2010121478A publication Critical patent/JP2010121478A/en
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
    • F01N3/18—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control
    • F01N3/20—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control specially adapted for catalytic conversion ; Methods of operation or control of catalytic converters
    • F01N3/2066—Selective catalytic reduction [SCR]
    • F01N3/208—Control of selective catalytic reduction [SCR], e.g. dosing of reducing agent
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N13/00—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00
    • F01N13/009—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00 having two or more separate purifying devices arranged in series
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
    • F01N3/105—General auxiliary catalysts, e.g. upstream or downstream of the main catalyst
    • F01N3/106—Auxiliary oxidation catalysts
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/02—Circuit arrangements for generating control signals
    • F02D41/021—Introducing corrections for particular conditions exterior to the engine
    • F02D41/0235—Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus
    • F02D41/027—Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus to purge or regenerate the exhaust gas treating apparatus
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2560/00—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics
    • F01N2560/02—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics the means being an exhaust gas sensor
    • F01N2560/026—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics the means being an exhaust gas sensor for measuring or detecting NOx
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2560/00—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics
    • F01N2560/06—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics the means being a temperature sensor
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2560/00—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics
    • F01N2560/14—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics having more than one sensor of one kind
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2610/00—Adding substances to exhaust gases
    • F01N2610/02—Adding substances to exhaust gases the substance being ammonia or urea
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2610/00—Adding substances to exhaust gases
    • F01N2610/14—Arrangements for the supply of substances, e.g. conduits
    • F01N2610/1453—Sprayers or atomisers; Arrangement thereof in the exhaust apparatus
    • F01N2610/146—Control thereof, e.g. control of injectors or injection valves
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2900/00—Details of electrical control or of the monitoring of the exhaust gas treating apparatus
    • F01N2900/06—Parameters used for exhaust control or diagnosing
    • F01N2900/14—Parameters used for exhaust control or diagnosing said parameters being related to the exhaust gas
    • F01N2900/1402—Exhaust gas composition
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2900/00—Details of electrical control or of the monitoring of the exhaust gas treating apparatus
    • F01N2900/06—Parameters used for exhaust control or diagnosing
    • F01N2900/16—Parameters used for exhaust control or diagnosing said parameters being related to the exhaust apparatus, e.g. particulate filter or catalyst
    • F01N2900/1622—Catalyst reducing agent absorption capacity or consumption amount
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/02—Circuit arrangements for generating control signals
    • F02D41/14—Introducing closed-loop corrections
    • F02D41/1401—Introducing closed-loop corrections characterised by the control or regulation method
    • F02D2041/1433—Introducing closed-loop corrections characterised by the control or regulation method using a model or simulation of the system
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/02—Circuit arrangements for generating control signals
    • F02D41/021—Introducing corrections for particular conditions exterior to the engine
    • F02D41/0235—Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus
    • F02D41/024—Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus to increase temperature of the exhaust gas treating apparatus
    • F02D41/0245—Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus to increase temperature of the exhaust gas treating apparatus by increasing temperature of the exhaust gas leaving the engine
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/02—Circuit arrangements for generating control signals
    • F02D41/04—Introducing corrections for particular operating conditions
    • F02D41/08—Introducing corrections for particular operating conditions for idling
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/02—Circuit arrangements for generating control signals
    • F02D41/14—Introducing closed-loop corrections
    • F02D41/1438—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor
    • F02D41/1444—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases
    • F02D41/1446—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases the characteristics being exhaust temperatures
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/30—Controlling fuel injection
    • F02D41/38—Controlling fuel injection of the high pressure type
    • F02D41/40—Controlling fuel injection of the high pressure type with means for controlling injection timing or duration
    • F02D41/402—Multiple injections
    • F02D41/405—Multiple injections with post injections
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A50/00—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE in human health protection, e.g. against extreme weather
    • Y02A50/20—Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/12—Improving ICE efficiencies

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Materials Engineering (AREA)
  • Health & Medical Sciences (AREA)
  • Toxicology (AREA)
  • Exhaust Gas After Treatment (AREA)
  • Exhaust Gas Treatment By Means Of Catalyst (AREA)

Abstract

<P>PROBLEM TO BE SOLVED: To solve such a problem that deposit caused by urea addition is accumulated on an inner wall of an exhaust gas passage 40 at low temperature and that controllability of ammonia supplied to urea SCR 52 deteriorates due to decomposition of the deposit at high temperature. <P>SOLUTION: If it is determined that accumulation quantity of deposit on an inner wall of an exhaust passage 40 is not less than a predetermined value, addition quantity of urea solution from a urea solution addition valve 62 is decreased. Thereafter, exhaust gas temperature is increased rapidly when request torque of a diesel engine 10 increases. Thus, the deposit having accumulated on the inner wall of the exhaust passage 40 is decomposed at once and is supplied to a urea SCR 52 as ammonia. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

本発明は、内燃機関の排気通路に設けられて且つ排気中の窒素酸化物を浄化する浄化手段と、前記浄化手段の上流側の排気中に還元剤を添加する添加手段とを備える排気浄化装置に適用され、前記添加手段の操作に基づき前記還元剤の添加量を調節しつつ前記浄化手段による窒素酸化物の浄化制御を行う内燃機関の排気浄化制御装置、及び排気浄化システムに関する。   The present invention provides an exhaust emission control device provided with a purification means provided in an exhaust passage of an internal combustion engine for purifying nitrogen oxides in exhaust gas, and an addition means for adding a reducing agent to the exhaust gas upstream of the purification means. The present invention relates to an exhaust gas purification control device for an internal combustion engine and an exhaust gas purification system that perform purification control of nitrogen oxides by the purification means while adjusting the amount of addition of the reducing agent based on the operation of the addition means.

近年、車載内燃機関（特にディーゼル機関）において、還元剤として尿素水を用いて排気中のＮＯｘ（窒素酸化物）を選択的に浄化する選択還元型触媒（ＳＣＲ：Selective Catalytic Reduction）を採用した排気浄化システム（尿素ＳＣＲシステム）の開発が進められており、一部実用化に至っている。尿素ＳＣＲシステムでは、機関本体に接続された排気管に選択還元型のＮＯｘ触媒が設けられるとともに、その上流側に、ＮＯｘ還元剤としての尿素水（尿素水溶液）を排気管内に添加する尿素水添加弁が設けられている。   In recent years, in-vehicle internal combustion engines (particularly diesel engines), exhaust that employs a selective catalytic reduction (SCR) that selectively purifies NOx (nitrogen oxides) in exhaust using urea water as a reducing agent. A purification system (urea SCR system) is being developed, and some have been put to practical use. In the urea SCR system, a selective reduction type NOx catalyst is provided in the exhaust pipe connected to the engine body, and urea water addition for adding urea water (urea aqueous solution) as a NOx reducing agent into the exhaust pipe is provided upstream of the exhaust gas. A valve is provided.

上記システムにおいては、尿素水添加弁により排気管内に尿素水が添加されることで、ＮＯｘ触媒上で排気中のＮＯｘが選択的に還元除去される。すなわち、尿素水が排気熱で加水分解されることによりアンモニア（ＮＨ３）が生成され、そのアンモニアがＮＯｘ触媒に吸着されるととともに同ＮＯｘ触媒上にてアンモニアによる還元反応が行われることによってＮＯｘが還元、浄化される。   In the above system, urea water is added into the exhaust pipe by the urea water addition valve, so that NOx in the exhaust gas is selectively reduced and removed on the NOx catalyst. That is, urea water is hydrolyzed by exhaust heat to generate ammonia (NH 3), and the ammonia is adsorbed to the NOx catalyst and the NOx is reduced on the NOx catalyst, so that NOx is reduced. Reduced and purified.

ところで、内燃機関の排気温度が低い場合には、尿素水からアンモニアへの加水分解効率が低下し、シアヌル酸等の尿素熱分解生成物が排気通路に析出するおそれがある。この析出物は排気温度が上昇することでアンモニアとなるため、排気通路に析出物が堆積している場合には、排気温度の上昇に伴ってＳＣＲに供給されるアンモニアが過剰となり、ＳＣＲへのアンモニア供給量の制御性が低下するおそれがある。   By the way, when the exhaust temperature of the internal combustion engine is low, the hydrolysis efficiency from urea water to ammonia decreases, and urea thermal decomposition products such as cyanuric acid may be deposited in the exhaust passage. This precipitate becomes ammonia when the exhaust temperature rises. Therefore, when the deposit is accumulated in the exhaust passage, the ammonia supplied to the SCR becomes excessive as the exhaust temperature rises, There is a possibility that the controllability of the ammonia supply amount may be lowered.

そこで従来、例えば下記特許文献１に見られるように、排気通路に微少量の排気を通過させるバイパス通路を設け、バイパス通路に尿素水の加水分解触媒とヒータとを備えることも提案されている。これにより、排気温度が低い場合には、バイパス通路を介して尿素水からアンモニアを抽出し、これをＮＯｘ触媒に供給することで、排気通路に尿素熱分解生成物が析出することを好適に抑制又は回避することができる。   Therefore, for example, as disclosed in Patent Document 1 below, it has been proposed to provide a bypass passage for allowing a small amount of exhaust to pass through the exhaust passage, and to provide a urea water hydrolysis catalyst and a heater in the bypass passage. Thereby, when the exhaust gas temperature is low, ammonia is extracted from the urea water through the bypass passage, and this is supplied to the NOx catalyst, so that the urea thermal decomposition product is suitably prevented from depositing in the exhaust passage. Or it can be avoided.

なお、従来の排気浄化制御装置としては、他にも例えば下記特許文献２に見られるものもある。
特開２００７−３２７３７７号公報 特開２００７−２３９５００号公報 In addition, as a conventional exhaust purification control device, there is another one that can be found, for example, in Patent Document 2 below.
JP 2007-327377 A JP 2007-239500 A

上記従来技術では、排気温度が低い領域におけるＮＯｘ浄化制御のために、バイパス通路や加水分解触媒、ヒータといったハードウェアを新たに備えることとなり、コストパフォーマンスが落ちることも無視できない。更に、ヒータを用いるため、エネルギ消費量が増大するという問題もある。   In the above prior art, hardware such as a bypass passage, a hydrolysis catalyst, and a heater are newly provided for NOx purification control in a region where the exhaust gas temperature is low, and it cannot be ignored that cost performance is lowered. Furthermore, since a heater is used, there is a problem that energy consumption increases.

本発明は、上記課題を解決するためになされたものであり、その目的は、浄化手段の上流側の排気中に還元剤を添加する添加手段を操作することで浄化手段による窒素酸化物の浄化制御を行うものにあって、部品点数の増加を抑制しつつも還元剤の添加に起因して排気通路に析出物が堆積することを好適に抑制することのできる内燃機関の排気浄化制御装置、及びこれを備える排気浄化システムを提供することにある。   The present invention has been made to solve the above-described problems, and an object of the present invention is to purify nitrogen oxides by purifying means by operating an adding means for adding a reducing agent into the exhaust gas upstream of the purifying means. An exhaust purification control device for an internal combustion engine that is capable of suitably controlling the deposition of deposits in the exhaust passage due to the addition of the reducing agent while suppressing an increase in the number of parts. And providing an exhaust purification system including the same.

以下、上記課題を解決するための手段、及びその作用効果について記載する。   Hereinafter, means for solving the above-described problems and the operation and effects thereof will be described.

請求項１記載の発明は、内燃機関の排気通路に設けられて且つ排気中の窒素酸化物を浄化する浄化手段と、前記浄化手段の上流側の排気中に還元剤を添加する添加手段とを備える排気浄化装置に適用され、前記添加手段の操作に基づき前記還元剤の添加量を調節しつつ前記浄化手段による窒素酸化物の浄化制御を行う内燃機関の排気浄化制御装置において、前記還元剤の添加に起因した前記排気通路内壁への析出物の堆積量を推定する推定手段と、前記推定される堆積量が規定値以上となること及び前記堆積量の増加速度が規定速度以上となることの少なくとも一方が成立する場合、前記還元剤の添加量を強制的に低減する低減手段とを備えることを特徴とする。   The invention according to claim 1 is provided with a purifying means that is provided in an exhaust passage of the internal combustion engine and purifies nitrogen oxides in the exhaust, and an adding means that adds a reducing agent to the exhaust gas upstream of the purifying means. In an exhaust gas purification control apparatus for an internal combustion engine that applies purification control of nitrogen oxides by the purification means while adjusting an amount of addition of the reducing agent based on an operation of the addition means. An estimation means for estimating the amount of deposits deposited on the inner wall of the exhaust passage due to the addition, the estimated amount of deposit is not less than a specified value, and the increase rate of the amount of deposit is not less than a specified rate. A reduction means for forcibly reducing the amount of the reducing agent added when at least one of them is established.

添加手段による還元剤の添加は、窒素酸化物の浄化のために行うものであるがゆえに、還元剤の添加量を低減することは、窒素酸化物の浄化率を低下させるおそれがある。ただし、発明者らは、排気通路内壁への析出物の堆積量が多くなる状況や、堆積量の増加速度が大きくなる状況にあっては、添加量を低減しても、窒素酸化物の浄化率の低下度合いが小さい又は無視できることを見出した。これは、次の理由による。すなわち、まず析出物の堆積量が多くなる状況下には、浄化手段への還元物質の吸着量が多くなるため、還元剤の添加量を低減したとしても、窒素酸化物の浄化にとっての添加量の不足分は、浄化手段内に吸着されている還元物質によって補償される。また、析出物の堆積物の増加速度が大きくなる状況下には、排気温度が低くなるため、排気中の窒素酸化物が減少する。   Since the addition of the reducing agent by the adding means is performed for the purification of nitrogen oxides, reducing the amount of the reducing agent added may reduce the nitrogen oxide purification rate. However, in the situation where the amount of deposits deposited on the inner wall of the exhaust passage increases or the rate of increase in the amount of deposits increases, the inventors purify nitrogen oxides even if the amount added is reduced. It was found that the rate of decrease was small or negligible. This is due to the following reason. That is, when the amount of deposits increases, the amount of reducing substance adsorbed on the purification means increases. Therefore, even if the amount of reducing agent added is reduced, the amount added to purify nitrogen oxides. This deficiency is compensated by the reducing substance adsorbed in the purification means. In addition, under a situation where the rate of increase in deposits increases, the exhaust gas temperature decreases, so that the nitrogen oxide in the exhaust gas decreases.

上記発明では、この点に鑑み、上記少なくとも一方の条件が成立する場合に還元剤の添加量を強制的に低減することで、排気通路内壁に析出物が堆積することを好適に抑制することができる。   In the above invention, in view of this point, when the at least one of the above conditions is satisfied, the amount of the reducing agent added is forcibly reduced, so that it is possible to suitably suppress deposits from depositing on the inner wall of the exhaust passage. it can.

請求項２記載の発明は、請求項１記載の発明において、前記推定される堆積量が所定値以上となる場合、前記内燃機関の排気温度を、前記析出物を除去可能な温度まで上昇させる排気温度上昇手段を更に備えることを特徴とする。   According to a second aspect of the present invention, in the first aspect of the invention, when the estimated accumulation amount is equal to or greater than a predetermined value, the exhaust temperature of the internal combustion engine is increased to a temperature at which the deposits can be removed. It further comprises a temperature raising means.

内燃機関に対する要求トルクの増大時等にあっては、排気温度が上昇するために排気通路内壁の堆積物が分解し、浄化手段へと供給される。ここで、排気通路内壁の堆積物が過度に多い場合には、上記要求トルクの増大時等において、浄化手段に過度の還元物質が供給されることとなり、これが浄化手段の下流側に多量に流出するおそれがある。上記発明では、この点に鑑み、排気通路内壁の堆積量が所定値以上となる場合に排気温度を上昇させることで、排気通路内壁の堆積量が過度に大きくなることを好適に抑制することができる。しかも、析出物を除去可能な温度まで上昇させるために、析出物の分解に起因した浄化手段への還元物質の供給量を比較的容易に把握することができるため、浄化手段への還元物質の供給制御を適切に行うこともできる。   When the required torque for the internal combustion engine increases, the exhaust temperature rises, so the deposit on the inner wall of the exhaust passage is decomposed and supplied to the purification means. Here, if the deposit on the inner wall of the exhaust passage is excessively large, excessive reducing material is supplied to the purification means when the required torque is increased, and a large amount of this flows out downstream of the purification means. There is a risk. In the above invention, in view of this point, it is possible to suitably suppress an excessive increase in the amount of accumulation on the inner wall of the exhaust passage by increasing the exhaust temperature when the amount of accumulation on the inner wall of the exhaust passage becomes a predetermined value or more. it can. Moreover, since the amount of the reducing substance supplied to the purification means due to the decomposition of the precipitate can be grasped relatively easily in order to raise the precipitate to a temperature at which the precipitate can be removed, Supply control can also be performed appropriately.

請求項３記載の発明は、請求項２記載の発明において、前記堆積量が所定以下となったと判断される場合、前記排気温度の上昇処理を停止することを特徴とする。   A third aspect of the invention is characterized in that, in the second aspect of the invention, the exhaust temperature increasing process is stopped when it is determined that the accumulation amount has become equal to or less than a predetermined value.

排気温度を上昇させる処理を行う場合、内燃機関の燃料消費量が増加するおそれがある。この点、上記発明では、堆積量が所定以下となる場合に排気温度の上昇処理を停止することで、燃料消費量が増加することを極力抑制することができる。   When processing for increasing the exhaust temperature is performed, the fuel consumption of the internal combustion engine may increase. In this regard, in the above-described invention, it is possible to suppress the increase in the fuel consumption as much as possible by stopping the exhaust temperature increase process when the accumulation amount is equal to or less than the predetermined amount.

請求項４記載の発明は、請求項１記載の発明において、前記内燃機関に対する要求トルクの増大時である場合、前記内燃機関の排気温度を、前記析出物を除去可能な温度まで前記内燃機関のトルクの増大に伴う上昇速度よりも急激に上昇させるトルク増大時上昇手段を更に備えることを特徴とする。   According to a fourth aspect of the present invention, in the first aspect of the invention, when the required torque for the internal combustion engine is increasing, the exhaust temperature of the internal combustion engine is set to a temperature at which the precipitate can be removed. It is further characterized by further comprising an increasing means at the time of torque increase that increases more rapidly than the speed of increase accompanying the increase in torque.

内燃機関に対する要求トルクの増大時にあっては、通常、内燃機関の排気温度が上昇するため、排気通路内壁の析出物が分解し、浄化手段に供給されるようになる。ただし、析出物の各成分毎に分解を開始する温度が相違するために、上記排気温度の上昇に伴って浄化手段に供給される還元物質量を把握することは困難である。上記発明では、この点に鑑み、内燃機関の要求トルクの増大時において排気温度を急激に上昇させることで、析出物の各成分が分解を開始する温度の相違による上記還元物質量の把握精度の低下を好適に抑制することができる。   When the required torque for the internal combustion engine increases, the exhaust temperature of the internal combustion engine usually rises, so that the deposit on the inner wall of the exhaust passage is decomposed and supplied to the purification means. However, since the temperature at which decomposition starts for each component of the deposit is different, it is difficult to grasp the amount of reducing substance supplied to the purification means as the exhaust gas temperature rises. In the above invention, in view of this point, the exhaust gas temperature is rapidly increased when the required torque of the internal combustion engine is increased, so that the accuracy of grasping the reducing substance amount due to the difference in temperature at which each component of the precipitate starts to decompose is improved. The decrease can be suitably suppressed.

請求項５記載の発明は、請求項２〜４のいずれか１項に記載の発明において、前記上昇手段による排気温度の上昇処理がなされる場合、前記添加手段による前記還元剤の添加量を低減することを特徴とする。   According to a fifth aspect of the present invention, in the invention according to any one of the second to fourth aspects, when the exhaust temperature is increased by the increasing means, the amount of the reducing agent added by the adding means is reduced. It is characterized by doing.

排気温度の上昇処理がなされると、排気通路内壁の析出物が分解し、これに起因して浄化手段に還元物質が供給される。このため、この際には、浄化手段に供給される還元物質が、添加手段によるものと上記分解に起因するものとの双方となる。このため、上記分解に起因する量を考慮することなく添加手段による添加量を設定したのでは、浄化手段に実際に供給される還元物質量が過剰となるおそれがある。上記発明では、この点に鑑み、排気温度の上昇処理がなされる場合、添加手段による還元剤の添加量を低減することで、上記分解に起因した浄化手段への還元物質の供給量の増加を好適に補償することができ、ひいては浄化手段に所望の量の還元物質を供給することができる。   When the exhaust gas temperature is increased, the deposit on the inner wall of the exhaust passage is decomposed, and as a result, the reducing substance is supplied to the purification means. For this reason, at this time, the reducing substance supplied to the purifying means is both due to the adding means and due to the decomposition. For this reason, if the addition amount by the addition means is set without considering the amount resulting from the decomposition, the amount of reducing substance actually supplied to the purification means may be excessive. In view of this point, in the above invention, when exhaust gas temperature increase processing is performed, the amount of reducing substance added to the purification means due to the decomposition is increased by reducing the amount of reducing agent added by the adding means. Compensation can be suitably performed and, in turn, a desired amount of reducing substance can be supplied to the purification means.

請求項６記載の発明は、請求項２〜５のいずれか１項に記載の発明において、前記上昇手段は、前記内燃機関の燃料噴射タイミングの遅角処理、前記内燃機関の排気通路への燃料の供給処理、及び前記内燃機関の排気還流量の増加処理の少なくとも１つを行うことを特徴とする。   According to a sixth aspect of the present invention, in the invention according to any one of the second to fifth aspects, the ascending means is a process of retarding the fuel injection timing of the internal combustion engine, and the fuel to the exhaust passage of the internal combustion engine And at least one of an increase process of the exhaust gas recirculation amount of the internal combustion engine.

請求項７記載の発明は、請求項２〜６のいずれか１項に記載の発明において、前記内燃機関は、車載内燃機関であり、前記内燃機関の出力軸は、変速装置を介して駆動輪に連結されるものであり、前記上昇手段は、前記変速装置の変速比を操作することで車両の走行速度の低下を抑制しつつ前記内燃機関の出力軸の回転速度を低下させるものであることを特徴とする。   The invention according to claim 7 is the invention according to any one of claims 2 to 6, wherein the internal combustion engine is an in-vehicle internal combustion engine, and an output shaft of the internal combustion engine is driven through a transmission. And the raising means lowers the rotational speed of the output shaft of the internal combustion engine while controlling the lowering of the traveling speed of the vehicle by operating the gear ratio of the transmission. It is characterized by.

内燃機関の回転速度を低下させると、内燃機関の燃焼室に充填される空気量が減少するため、排気温度を上昇させることができる。   When the rotational speed of the internal combustion engine is reduced, the amount of air charged in the combustion chamber of the internal combustion engine is reduced, so that the exhaust temperature can be raised.

請求項８記載の発明は、請求項１〜７のいずれか１項に記載の発明において、前記推定手段は、前記内燃機関の排気系の温度と相関を有するパラメータ及び前記添加量に基づき、前記堆積量を推定することを特徴とする。   The invention according to claim 8 is the invention according to any one of claims 1 to 7, wherein the estimating means is based on a parameter having a correlation with a temperature of an exhaust system of the internal combustion engine and the addition amount. It is characterized by estimating the amount of deposition.

上記発明では、堆積量と相関を有するパラメータである上記排気系の温度と相関を有するパラメータ及び添加量を用いることで、堆積量を適切に推定することができる。   In the above invention, the deposition amount can be appropriately estimated by using the parameter and the addition amount having a correlation with the temperature of the exhaust system, which is a parameter having a correlation with the deposition amount.

請求項９記載の発明は、請求項１〜８のいずれか１項に記載の発明において、前記推定手段は、前記内燃機関のアイドル運転時、当該アイドル運転のなされる時間に基づき前記堆積量を推定することを特徴とする。   According to a ninth aspect of the present invention, in the invention according to any one of the first to eighth aspects, the estimating means calculates the accumulation amount based on a time during which the internal combustion engine is idle during the idle operation. It is characterized by estimating.

内燃機関のアイドル運転時においては、排気温度が低いことから、排気通路内壁に析出物が堆積しやすい。そして、この析出物の堆積量は、アイドル時間が長いほど多くなる。上記発明では、この点に鑑み、アイドル時間を堆積量と相関を有するパラメータとして利用することで堆積量を好適に推定することができる。   During idle operation of the internal combustion engine, the exhaust temperature is low, so that deposits are likely to accumulate on the inner wall of the exhaust passage. And the deposit amount of this deposit increases, so that idle time is long. In the above invention, in view of this point, the accumulation amount can be suitably estimated by using the idle time as a parameter having a correlation with the accumulation amount.

請求項１０記載の発明は、請求項１〜９のいずれか１項に記載の発明において、前記還元剤が尿素水であることを特徴とする。   The invention described in claim 10 is the invention described in any one of claims 1-9, wherein the reducing agent is urea water.

尿素水を還元剤とする場合、十分に加熱されない状況下にあっては、排気通路の内壁に尿素熱分解生成物が析出する。しかも、この析出物は、様々な成分を有し、各成分毎に分解開始温度が相違する。このため、析出物の分解による浄化手段への還元物質の供給量の増加が、還元物質の供給制御の制御性を低下させる要因となる。このため、上記発明は、低減手段や上昇手段の利用価値が特に大きい。   When urea water is used as the reducing agent, the urea thermal decomposition product is deposited on the inner wall of the exhaust passage under a situation where the urea water is not sufficiently heated. In addition, the precipitate has various components, and the decomposition start temperature is different for each component. For this reason, the increase in the supply amount of the reducing substance to the purification means due to the decomposition of the precipitates becomes a factor that reduces the controllability of the supply control of the reducing substance. For this reason, the said invention has especially big utility value of a reduction means and a raising means.

請求項１１記載の発明は、請求項１〜１０のいずれか１項に記載の内燃機関の排気浄化制御装置と、前記浄化手段とを備えることを特徴とする内燃機関の排気浄化システムである。   An eleventh aspect of the present invention is an exhaust gas purification system for an internal combustion engine comprising the exhaust gas purification control device for an internal combustion engine according to any one of the first to tenth aspects and the purification means.

上記発明は、低減手段や上昇手段を備えるために、信頼性の高いシステムを実現している。   Since the above invention includes a reducing means and a raising means, a highly reliable system is realized.

（第１の実施形態）
以下、本発明にかかる内燃機関の排気浄化制御装置の第１の実施形態を図面を参照しつつ説明する。 (First embodiment)
Hereinafter, a first embodiment of an exhaust gas purification control apparatus for an internal combustion engine according to the present invention will be described with reference to the drawings.

ディーゼル機関１０は、レシプロエンジン構造を有する内燃機関である。ディーゼル機関１０の吸気通路１２の上流には、エアクリーナ１４が設けられており、エアクリーナ１４には、吸気温度を検出する吸気温センサ１６や、吸気流量を検出するエアフローメータ１８が設けられている。エアクリーナ１４の下流には、ターボチャージャ２０が設けられている。そして、ターボチャージャ２０によって過給された空気は、インタークーラ２２によって冷却された後、吸気通路１２の下流側に供給される。この空気は、吸気通路１２の流路面積を調節するスロットルバルブ２４やディーゼル機関１０の燃焼室２８及び吸気通路１２間を開閉する吸気バルブ２６を介して、燃焼室２８に供給される。   The diesel engine 10 is an internal combustion engine having a reciprocating engine structure. An air cleaner 14 is provided upstream of the intake passage 12 of the diesel engine 10. The air cleaner 14 is provided with an intake air temperature sensor 16 that detects the intake air temperature and an air flow meter 18 that detects the intake air flow rate. A turbocharger 20 is provided downstream of the air cleaner 14. The air supercharged by the turbocharger 20 is cooled by the intercooler 22 and then supplied to the downstream side of the intake passage 12. This air is supplied to the combustion chamber 28 via a throttle valve 24 that adjusts the flow passage area of the intake passage 12, a combustion chamber 28 of the diesel engine 10, and an intake valve 26 that opens and closes the intake passage 12.

こうして燃焼室２８に供給された空気は、燃焼室２８に先端部が突出する燃料噴射弁３０によって噴射された高圧(例えば「数十〜２００ＭＰａ」)の燃料(例えば軽油)とともに圧縮され、燃焼に供される。この燃焼によって生成されるエネルギは、ピストン３２を介してクランク軸３４の回転エネルギに変換される。クランク軸３４の回転エネルギは、無段変速装置（ＣＶＴ３５)を介して、駆動輪に伝達される。ちなみに、クランク軸３４付近には、その回転角度を検出するクランク角センサ３６が設けられている。   The air thus supplied to the combustion chamber 28 is compressed together with high-pressure (for example, “several tens to 200 MPa”) fuel (for example, light oil) injected by the fuel injection valve 30 whose front end projects into the combustion chamber 28, and is combusted. Provided. The energy generated by this combustion is converted into rotational energy of the crankshaft 34 via the piston 32. The rotational energy of the crankshaft 34 is transmitted to the drive wheels via a continuously variable transmission (CVT 35). Incidentally, a crank angle sensor 36 for detecting the rotation angle is provided near the crankshaft 34.

燃焼室２８において燃焼に供された上記空気及び燃料は、排気バルブ３８の開動作に伴って、排気として排気通路４０に排出される。排気通路４０のうち、ターボチャージャ２０の上流は、排気還流通路４２を介して吸気通路１２に接続されており、排気還流通路４２の流路面積を調節する排気還流バルブ（ＥＧＲバルブ４６）の開度に応じて、排気通路４０に排出された排気の一部が、ＥＧＲクーラ４４によって冷却された後に、吸気通路１２に供給される。   The air and fuel used for combustion in the combustion chamber 28 are discharged into the exhaust passage 40 as exhaust gas as the exhaust valve 38 is opened. Of the exhaust passage 40, the upstream of the turbocharger 20 is connected to the intake passage 12 via the exhaust recirculation passage 42, and an exhaust recirculation valve (EGR valve 46) that adjusts the flow area of the exhaust recirculation passage 42 is opened. Depending on the degree, a part of the exhaust discharged to the exhaust passage 40 is cooled by the EGR cooler 44 and then supplied to the intake passage 12.

排気通路４０のうちターボチャージャ２０の下流には、後処理装置が設けられている。後処理装置は、排気通路４０の上流側から順に、酸化触媒５０、尿素選択還元型触媒(以下、尿素ＳＣＲ５２)、及びアンモニアスリップ触媒５４を備えて構成される。ここで、アンモニアスリップ触媒５４は、尿素ＳＣＲ５２においてＮＯｘと反応しきれずに余剰となったアンモニアが尿素ＳＣＲ５２の下流に排出される場合に、これを除去するためのものである。アンモニアスリップ触媒５４は、例えば酸化触媒にて構成されている。   A post-processing device is provided downstream of the turbocharger 20 in the exhaust passage 40. The post-treatment device includes an oxidation catalyst 50, a urea selective reduction catalyst (hereinafter referred to as urea SCR 52), and an ammonia slip catalyst 54 in order from the upstream side of the exhaust passage 40. Here, the ammonia slip catalyst 54 is used to remove ammonia that has not reacted with NOx and has been exhausted downstream of the urea SCR 52 in the urea SCR 52. The ammonia slip catalyst 54 is composed of, for example, an oxidation catalyst.

酸化触媒５０と尿素ＳＣＲ５２との間には、排気中のＮＯｘ濃度を検出する上流側ＮＯｘセンサ５６と、排気温度を検出する排気温センサ５８とが設けられている。また、尿素ＳＣＲ５２とアンモニアスリップ触媒５４との間には、ＮＯｘ濃度を検出する下流側ＮＯｘセンサ６０が設けられている。なお、後処理装置は、更に、排気中の粒子状物質（ＰＭ）を捕集するディーゼルパティキュレートフィルタ（ＤＰＦ）を備えているが、これについては、酸化触媒５０と一体とされるものとしてもよいし、また、その下流に備えられるとしてもよい。   Between the oxidation catalyst 50 and the urea SCR 52, an upstream NOx sensor 56 for detecting the NOx concentration in the exhaust gas and an exhaust temperature sensor 58 for detecting the exhaust gas temperature are provided. Further, a downstream NOx sensor 60 that detects the NOx concentration is provided between the urea SCR 52 and the ammonia slip catalyst 54. The post-treatment device further includes a diesel particulate filter (DPF) that collects particulate matter (PM) in the exhaust gas. However, this may be integrated with the oxidation catalyst 50. It may also be provided downstream thereof.

上記酸化触媒５０と尿素ＳＣＲ５２との間には、更に、排気通路４０の下流側に噴射口を設けた尿素水添加弁６２が設けられている。尿素水添加弁６２は、尿素水タンク６４から供給される尿素水を排気通路４０内に噴射することで、尿素水を排気に添加する電子制御式の弁体である。尿素水タンク６４は給液キャップ付きの密閉容器にて構成されており、その内部に所定濃度（例えば３２．５％）の尿素水が貯蔵されている。尿素水タンク６４は、尿素水配管６６を介して尿素水添加弁６２に接続されており、尿素水配管６６の途中には、尿素水タンク６４内の尿素水を汲み上げ尿素水添加弁６２に加圧供給(圧送)する電子制御式の尿素水ポンプ６８が設けられている。なお、尿素水ポンプ６８の下流には、圧送される尿素水の圧力を検出する圧力センサ７０が設けられている。   Between the oxidation catalyst 50 and the urea SCR 52, a urea water addition valve 62 having an injection port provided downstream of the exhaust passage 40 is further provided. The urea water addition valve 62 is an electronically controlled valve body that adds urea water to exhaust gas by injecting urea water supplied from the urea water tank 64 into the exhaust passage 40. The urea water tank 64 is configured by a sealed container with a liquid supply cap, and urea water having a predetermined concentration (for example, 32.5%) is stored therein. The urea water tank 64 is connected to the urea water addition valve 62 via the urea water pipe 66, and the urea water in the urea water tank 64 is pumped up and added to the urea water addition valve 62 in the middle of the urea water pipe 66. An electronically controlled urea water pump 68 for supplying pressure (pressure feeding) is provided. A pressure sensor 70 that detects the pressure of the urea water that is pumped is provided downstream of the urea water pump 68.

上記尿素水添加弁６２の上流には、排気通路４０内を流れる排気に旋回流を生じさせるための旋回流発生部材７２が設けられている。旋回流発生部材７２は、排気通路４０内の流通経路の断面構造を変更することで、排気に旋回流を生成する部材である。   A swirling flow generating member 72 for generating a swirling flow in the exhaust gas flowing in the exhaust passage 40 is provided upstream of the urea water addition valve 62. The swirl flow generating member 72 is a member that generates a swirl flow in the exhaust by changing the cross-sectional structure of the flow path in the exhaust passage 40.

上記尿素ＳＣＲ５２や尿素水添加弁６２等を備えて構成される尿素ＳＣＲシステムでは、尿素水添加弁６２により排気通路４０内に尿素水を添加供給することで、排気通路４０内において排気と共に尿素水が尿素ＳＣＲ５２に供給される。これにより、尿素ＳＣＲ５２においては、ＮＯｘの還元反応が行われることによってその排気が浄化される。   In the urea SCR system configured to include the urea SCR 52, the urea water addition valve 62, and the like, urea water is added to the exhaust passage 40 by the urea water addition valve 62 to supply urea water together with the exhaust in the exhaust passage 40. Is supplied to the urea SCR 52. Thus, the urea SCR 52 purifies the exhaust gas by performing a NOx reduction reaction.

詳しくは、尿素水添加弁６２から噴射された尿素水が排気熱で加水分解され、その際、下記の式（ｃ１）にて表現される化学反応にて、還元物質としてのアンモニア（ＮＨ３）が生成される。   Specifically, the urea water injected from the urea water addition valve 62 is hydrolyzed by the exhaust heat, and in this case, ammonia (NH3) as a reducing substance is converted by a chemical reaction expressed by the following formula (c1). Generated.

（ＮＨ２）２ＣＯ＋Ｈ２Ｏ→２ＮＨ３＋ＣＯ２ …（ｃ１）
そして、尿素ＳＣＲ５２を排気が通過する際、アンモニアによって排気中のＮＯｘが選択的に還元浄化される。詳しくは、以下の式（ｃ２）〜（ｃ４）に示すような還元反応が行われることによって、ＮＯｘが還元浄化されることになる。 (NH2) 2CO + H2O → 2NH3 + CO2 (c1)
When the exhaust gas passes through the urea SCR 52, NOx in the exhaust gas is selectively reduced and purified by ammonia. Specifically, NOx is reduced and purified by performing a reduction reaction as shown in the following formulas (c2) to (c4).

４ＮＯ＋４ＮＨ３＋Ｏ２→４Ｎ２＋６Ｈ２Ｏ …（ｃ２）
６ＮＯ２＋８ＮＨ３→７Ｎ２＋１２Ｈ２Ｏ …（ｃ３）
ＮＯ＋ＮＯ２＋２ＮＨ３→２Ｎ２＋３Ｈ２Ｏ …（ｃ４）
電子制御装置（ＥＣＵ８０）は、ディーゼル機関１０を制御対象とし、燃料噴射弁３０等の各種アクチュエータを操作する制御装置である。ＥＣＵ８０は、ディーゼル機関１０の運転状態を検出する上述した各種センサの検出信号や、ユーザによるアクセル操作量を検出するためのアクセルセンサ８２の検出信号、車両の走行速度を検出する車速センサ８４の検出信号等を逐次入力し、これらに基づき、ディーゼル機関１０の制御量（トルク、排気特性等）を制御する。 4NO + 4NH3 + O2 → 4N2 + 6H2O (c2)
6NO2 + 8NH3 → 7N2 + 12H2O (c3)
NO + NO2 + 2NH3 → 2N2 + 3H2O (c4)
The electronic control unit (ECU 80) is a control unit that controls the diesel engine 10 and operates various actuators such as the fuel injection valve 30. The ECU 80 detects the detection signals of the above-described various sensors that detect the operating state of the diesel engine 10, the detection signal of the accelerator sensor 82 for detecting the amount of accelerator operation by the user, and the detection of the vehicle speed sensor 84 that detects the traveling speed of the vehicle. A signal or the like is sequentially input, and the control amount (torque, exhaust characteristics, etc.) of the diesel engine 10 is controlled based on these signals.

特にＥＣＵ８０は、上記制御量としての排気通路４０から排出される排気の特性を制御すべく、尿素水添加弁６２や尿素水ポンプ６８を操作することで、尿素ＳＣＲ５２によるＮＯｘの浄化制御を行う。ここではまず、上流側ＮＯｘセンサ５６によって検出される排気中のＮＯｘ濃度に基づき、尿素水添加量を算出する。そして、算出された尿素水添加量に基づき尿素水添加弁６２に対して所定周期の開弁指令パルスを出力する。このパルス出力に伴って尿素水添加弁６２の駆動部（ソレノイド部）に駆動電流が流れることで、尿素水添加弁６２が開弁され、尿素水が添加（噴射）される。   In particular, the ECU 80 controls the NOx purification by the urea SCR 52 by operating the urea water addition valve 62 and the urea water pump 68 to control the characteristics of the exhaust gas discharged from the exhaust passage 40 as the control amount. Here, first, the urea water addition amount is calculated based on the NOx concentration in the exhaust gas detected by the upstream side NOx sensor 56. Based on the calculated urea water addition amount, a valve opening command pulse having a predetermined cycle is output to the urea water addition valve 62. With this pulse output, a drive current flows through the drive unit (solenoid unit) of the urea water addition valve 62, whereby the urea water addition valve 62 is opened and urea water is added (injected).

ところで、ディーゼル機関１０の排気系の温度が低い場合には、尿素水からアンモニアへの加水分解効率が低下し、シアヌル酸等の尿素熱分解生成物が析出し、排気通路４０の内壁面に堆積されるおそれがある。ここで排気通路４０内壁に堆積された析出物は、排気温度が上昇するに連れて分解し、アンモニアを発生させる。このため、排気通路４０内壁に堆積された析出物が分解することで、尿素水添加弁６２の操作にかかわらず、尿素ＳＣＲ５２にアンモニアが供給されることとなる。ただし、上記析出物には様々な成分が存在し、成分毎に分解し始める温度が相違する。図２に、上記析出物を構成する成分のうちのビューレットとシアヌール酸との分解開始温度(融点)を示す。詳しくは、図２は、酸素雰囲気下におけるビューレットとシアヌール酸との分解開始温度の計測結果である。図示されるように、ビューレットとシアヌール酸との分解開始温度は、「１００°Ｃ」も相違する。このため、排気温度の上昇に伴って排気通路４０内壁の析出物がどれだけ分解し、これに起因して尿素ＳＣＲ５２にアンモニアが供給されるようになるかを予測することは極めて困難である。   By the way, when the temperature of the exhaust system of the diesel engine 10 is low, the hydrolysis efficiency from urea water to ammonia is reduced, and urea thermal decomposition products such as cyanuric acid are deposited and deposited on the inner wall surface of the exhaust passage 40. There is a risk of being. Here, the deposit deposited on the inner wall of the exhaust passage 40 is decomposed as the exhaust temperature rises to generate ammonia. For this reason, the deposit deposited on the inner wall of the exhaust passage 40 is decomposed, so that ammonia is supplied to the urea SCR 52 regardless of the operation of the urea water addition valve 62. However, there are various components in the precipitate, and the temperature at which decomposition begins for each component is different. FIG. 2 shows the decomposition start temperature (melting point) of burette and cyanuric acid among the components constituting the precipitate. Specifically, FIG. 2 is a measurement result of the decomposition start temperature of burette and cyanuric acid in an oxygen atmosphere. As shown in the figure, the decomposition start temperature of burette and cyanuric acid is different by “100 ° C.”. For this reason, it is extremely difficult to predict how much the deposits on the inner wall of the exhaust passage 40 will be decomposed as the exhaust gas temperature rises, and as a result, ammonia will be supplied to the urea SCR 52.

更に、上記析出物は、時間の経過とともにその成分濃度を変化させ得る。図３に、上記析出物を構成する成分のうちのビューレット、アンメリド及びシアヌール酸の組成割合の経時変化を示す。詳しくは、図３は、固体の尿素を「１８０°Ｃ」にて加熱処理した際の加熱時間と、固体として残存する成分の各組成割合との関係の計測結果である。図示されるように、加熱処理時間が長くなるにつれて、シアヌール酸の組成割合が増加していく。換言すれば、分解開始温度が高い成分の組成割合が増加していく。こうした現象は、排気温度の上昇に伴って排気通路４０内壁の析出物がどれだけ分解し、これに起因して尿素ＳＣＲ５２にアンモニアが供給されるようになるかを予測することを更に困難なものとする。   Furthermore, the said deposit can change the component density | concentration with progress of time. FIG. 3 shows changes with time in the composition ratios of burette, ammelide and cyanuric acid among the components constituting the precipitate. Specifically, FIG. 3 is a measurement result of the relationship between the heating time when solid urea is heat-treated at “180 ° C.” and the composition ratios of the components remaining as solids. As illustrated, the composition ratio of cyanuric acid increases as the heat treatment time increases. In other words, the composition ratio of a component having a high decomposition start temperature increases. This phenomenon makes it more difficult to predict how much the deposit on the inner wall of the exhaust passage 40 will decompose as the exhaust gas temperature rises, and as a result, ammonia will be supplied to the urea SCR 52. And

そこで本実施形態では、図４〜図６に示す処理によって、尿素ＳＣＲ５２へのアンモニア供給量が過度に多くなる事態を好適に回避する。   Therefore, in the present embodiment, the process shown in FIGS. 4 to 6 suitably avoids a situation where the ammonia supply amount to the urea SCR 52 becomes excessively large.

図４は、本実施形態における第１の処理態様を示すものである。詳しくは、図４（ａ）に、車両の走行速度の推移を示し、図４（ｂ）に、排気温度の推移を示し、図４（ｃ）に、尿素水添加量の推移を示し、図４（ｄ）に、排気通路４０内壁への尿素析出物堆積量の推移を示し、図４（ｅ）に、ＮＯｘ浄化率の推移を示す。なお、ＮＯｘ浄化率とは、尿素ＳＣＲ５２の上流側のＮＯｘ濃度と下流側のＮＯｘ濃度との差を、上流側のＮＯｘ濃度によって除算した値にて定量化されるものである。   FIG. 4 shows a first processing mode in the present embodiment. Specifically, FIG. 4 (a) shows the transition of the running speed of the vehicle, FIG. 4 (b) shows the transition of the exhaust temperature, FIG. 4 (c) shows the transition of the urea water addition amount, 4 (d) shows the transition of the amount of urea deposits deposited on the inner wall of the exhaust passage 40, and FIG. 4 (e) shows the transition of the NOx purification rate. The NOx purification rate is quantified by a value obtained by dividing the difference between the upstream NOx concentration and the downstream NOx concentration of the urea SCR 52 by the upstream NOx concentration.

この第１の処理は、排気通路４０内壁への尿素析出物堆積量が増加する場合、尿素添加量を低減する処理である。詳しくは、本実施形態では、後述する尿素析出物堆積量が閾値β以上となって且つ、排気温度が閾値温度γ以下である場合に、尿素添加量を低減する。ここで排気温度が閾値温度γ以下との条件を設けたのは、尿素析出物の堆積量が多くなる状況をより高精度に見極めるためである。図では、時刻ｔ３において排気温が閾値温度γ以下となることで、尿素水添加量の低減制御を行っている。このように尿素水添加量の低減制御を行うことで、排気通路４０内壁への尿素析出物の堆積量の増加を好適に抑制することができる。ここで、尿素水添加量は、本来、ＮＯｘの浄化のために要求される量に設定されるものである。このため、尿素水添加量をいたずらに低減することは、後処理装置の下流側に排出される排気中のＮＯｘ濃度を上昇させることにつながるおそれがある。しかし、排気通路４０内壁への析出物堆積量が増加する状況下にあっては、尿素ＳＣＲ５２内に吸着されるアンモニアも増加しており、尿素水添加量の低減による尿素ＳＣＲ５２へのアンモニア供給量の減少は、尿素ＳＣＲ５２内に吸着されているアンモニアによって補償可能であることが発明者らによって見出された。ここで、吸着されるアンモニア量の増加は、図の時刻ｔ２以降、排気温度の低下に起因してＮＯｘ浄化率が低下するために生じるものである。本実施形態では、この知見に基づき、上記尿素水添加量の低減制御を行う。実際、図４に示す例では、尿素水添加量の低減制御によって、ＮＯｘ浄化率は低下していない。   The first process is a process of reducing the urea addition amount when the urea deposit accumulation amount on the inner wall of the exhaust passage 40 increases. Specifically, in the present embodiment, the urea addition amount is reduced when the urea deposit accumulation amount described later is equal to or higher than the threshold value β and the exhaust temperature is equal to or lower than the threshold temperature γ. Here, the condition that the exhaust gas temperature is equal to or lower than the threshold temperature γ is set in order to determine the situation in which the amount of urea deposits increases with higher accuracy. In the figure, the urea water addition amount is controlled to be reduced when the exhaust gas temperature becomes equal to or lower than the threshold temperature γ at time t3. Thus, by performing the reduction control of the urea water addition amount, it is possible to suitably suppress an increase in the amount of urea deposits deposited on the inner wall of the exhaust passage 40. Here, the urea water addition amount is originally set to an amount required for NOx purification. For this reason, reducing the urea water addition amount unnecessarily may lead to an increase in the NOx concentration in the exhaust discharged to the downstream side of the aftertreatment device. However, under the situation where the amount of deposits deposited on the inner wall of the exhaust passage 40 increases, the amount of ammonia adsorbed in the urea SCR 52 also increases, and the amount of ammonia supplied to the urea SCR 52 by reducing the amount of urea water added. It has been found by the inventors that this decrease can be compensated by ammonia adsorbed in the urea SCR52. Here, the increase in the amount of adsorbed ammonia occurs because the NOx purification rate decreases due to the decrease in the exhaust temperature after time t2 in the figure. In this embodiment, the urea water addition amount is controlled to be reduced based on this knowledge. Actually, in the example shown in FIG. 4, the NOx purification rate is not lowered by the reduction control of the urea water addition amount.

図５は、本実施形態における第２の処理態様を示すものである。なお、図５（ａ）〜図５（ｅ）は、先の図４（ａ）〜図４（ｅ）に対応している。   FIG. 5 shows a second processing mode in the present embodiment. 5A to FIG. 5E correspond to the previous FIG. 4A to FIG. 4E.

この第２の処理は、排気通路４０内壁の尿素析出物堆積量が閾値α以上となることで、排気温度を上昇させる処理(昇温制御)を行うものである。図５では、時刻ｔ３において、堆積量が閾値α以上となることで昇温制御を実行し、その後堆積量が閾値β以下となることで昇温制御を停止する。同様に、時刻ｔ５〜ｔ６、ｔ７〜ｔ８においても昇温制御を行う。ここで、昇温制御は、排気温度を、排気通路４０内壁に堆積される析出物の分解開始温度の最大値以上に急激に上昇させる処理とする。詳しくは、排気温度を「３００°Ｃ」までステップ状に上昇させる処理とする。ここで、ステップ状の上昇とは、ディーゼル機関１０の通常の要求トルクの増大時等に起因した排気温度の平均的な上昇速度よりも大きな速度での上昇とする。これにより、析出物の分解に起因して尿素ＳＣＲ５２へ供給されるアンモニアの量を容易に予測することができる。このため、尿素水添加弁６２からの尿素水添加量の減少量を、析出物の分解に起因して予測されるアンモニア供給量に基づき減少させることができる。図では、尿素水添加量を強制的に減少させる例として、昇温制御の開始に伴って尿素水添加量を漸減させ、所定量となることで固定する例を示している。   In the second process, the urea precipitate accumulation amount on the inner wall of the exhaust passage 40 is equal to or greater than the threshold value α, so that the process of increasing the exhaust temperature (temperature increase control) is performed. In FIG. 5, at time t <b> 3, the temperature increase control is executed when the accumulation amount becomes equal to or greater than the threshold value α, and then the temperature increase control is stopped when the accumulation amount becomes equal to or less than the threshold value β. Similarly, temperature rise control is performed at times t5 to t6 and t7 to t8. Here, the temperature rise control is a process in which the exhaust temperature is rapidly increased to a value equal to or higher than the maximum decomposition start temperature of the deposit deposited on the inner wall of the exhaust passage 40. Specifically, the exhaust temperature is increased to “300 ° C.” in a stepwise manner. Here, the step-like increase refers to an increase at a speed larger than the average increase speed of the exhaust temperature caused by an increase in the normal required torque of the diesel engine 10 or the like. Thereby, the amount of ammonia supplied to the urea SCR 52 due to the decomposition of the precipitate can be easily predicted. For this reason, the decrease amount of the urea water addition amount from the urea water addition valve 62 can be reduced based on the ammonia supply amount predicted due to the decomposition of the precipitate. In the figure, as an example of forcibly decreasing the urea water addition amount, an example is shown in which the urea water addition amount is gradually decreased with the start of the temperature increase control and fixed by reaching a predetermined amount.

上記昇温制御は、ポスト噴射、ＥＧＲ量の増加処理、及びＣＶＴ３５の変速比の増加処理の少なくとも１つによって行えばよい。ここで、ポスト噴射は、ディーゼル機関１０の圧縮上死点よりもかなり遅角側にて燃焼室２８に燃料を噴射するものであり、これにより、噴射された燃料を燃焼室２８ではなく排気通路４０において燃焼させるものである。また、ＥＧＲ量の増加処理は、ＥＧＲバルブ４６の開度を増加操作することで行うことができる。ＥＧＲ量が増加すると、吸気通路１２から燃焼室２８に供給される気体の温度が上昇するため、排気温度を上昇させることができる。更に、ＣＶＴ３５の変速比の増加処理は、車両の走行速度を低下させることなく、ディーゼル機関１０の回転速度を低下させるために行われるものである。ディーゼル機関１０の回転速度が低下する場合、燃焼室２８に供給される気体の充填量が減少するため、単位燃料当たりの空気量が減少し、ひいては排気温度が上昇する。   The temperature increase control may be performed by at least one of post-injection, EGR amount increase processing, and CVT 35 speed ratio increase processing. Here, the post-injection is to inject fuel into the combustion chamber 28 at a considerably retarded angle side relative to the compression top dead center of the diesel engine 10, whereby the injected fuel is not in the combustion chamber 28 but in the exhaust passage. 40 to burn. Further, the EGR amount increasing process can be performed by increasing the opening degree of the EGR valve 46. When the EGR amount increases, the temperature of the gas supplied from the intake passage 12 to the combustion chamber 28 increases, so that the exhaust temperature can be increased. Furthermore, the process of increasing the transmission ratio of the CVT 35 is performed in order to reduce the rotational speed of the diesel engine 10 without reducing the traveling speed of the vehicle. When the rotational speed of the diesel engine 10 decreases, the amount of gas supplied to the combustion chamber 28 decreases, so the amount of air per unit fuel decreases, and the exhaust temperature increases.

図６は、本実施形態における第３の処理態様を示すものである。なお、図６（ａ）〜図６（ｄ）は、先の図４（ａ）〜図４（ｄ）に対応している。   FIG. 6 shows a third processing mode in the present embodiment. 6A to FIG. 6D correspond to the previous FIG. 4A to FIG. 4D.

この第３の処理は、ディーゼル機関１０の加速要求時、加速要求に伴う排気温度の上昇速度よりも急激に排気温度を上記析出物の分解開始温度の最大値以上に上昇させる処理である。詳しくは、排気温度を「３００°Ｃ」までステップ状に上昇させる処理である。すなわち、加速要求が生じる場合には、排気温度が上昇するため、排気通路４０内壁に堆積している析出物も分解するものの、析出物の成分によって分解開始温度が相違することなどから、どのタイミングでどれだけのアンモニアが発生することとなるかを把握することは困難である。このため、析出物の分解に起因したアンモニアの発生量を容易に予測可能とすべく、排気温度をステップ状に上昇させる。これにより、尿素水添加弁６２から添加される尿素水添加量を適切な量とすることが容易となる。   This third process is a process of increasing the exhaust temperature more rapidly than the maximum value of the precipitate decomposition start temperature when the diesel engine 10 is requested to accelerate than the rate of increase of the exhaust temperature accompanying the acceleration request. Specifically, this is a process of increasing the exhaust temperature to “300 ° C.” stepwise. That is, when an acceleration request is generated, the exhaust temperature rises, so the deposits deposited on the inner wall of the exhaust passage 40 are also decomposed, but the timing at which the decomposition starts differs depending on the components of the precipitates. Therefore, it is difficult to grasp how much ammonia will be generated. For this reason, the exhaust gas temperature is raised stepwise so that the amount of ammonia generated due to the decomposition of the precipitate can be easily predicted. Thereby, it becomes easy to make the urea water addition amount added from the urea water addition valve 62 an appropriate amount.

なお、本実施形態にかかる昇温制御は、ポスト噴射によって行えばよい。   The temperature increase control according to the present embodiment may be performed by post injection.

図７に、本実施形態にかかる窒素酸化物の浄化処理の手順を示す。この処理は、ＥＣＵ８０によって、例えば所定周期で繰り返し実行される。   FIG. 7 shows the procedure of the nitrogen oxide purification process according to the present embodiment. This process is repeatedly executed by the ECU 80, for example, at a predetermined cycle.

この一連の処理では、まずステップＳ１０において、ディーゼル機関１０の現在の運転領域が、尿素水の添加処理を行う領域であるか否かを判断する。ここで、尿素水の添加処理を行う領域は、例えば尿素ＳＣＲ５２の温度が活性状態となる温度以上の領域とすればよい。そして、尿素水の添加処理を行う領域である場合、ステップＳ１２において、排気通路４０内壁の温度及び尿素水添加量に基づき、尿素析出物の堆積量を推定する。ここでは、内壁温度が低いほど堆積量が多いと推定し、また、尿素水添加量が多いほど堆積量が多いと推定する。   In this series of processes, first, in step S10, it is determined whether or not the current operation region of the diesel engine 10 is a region in which urea water addition processing is performed. Here, the region where the urea water addition process is performed may be a region equal to or higher than the temperature at which the temperature of the urea SCR 52 becomes active. If it is the region where the urea water addition process is performed, in step S12, the deposition amount of urea precipitates is estimated based on the temperature of the inner wall of the exhaust passage 40 and the urea water addition amount. Here, it is estimated that the lower the inner wall temperature, the greater the amount of deposition, and the greater the amount of urea water added, the greater the amount of deposition.

上記排気通路４０の内壁の温度は、車速センサ８４によって検出される車速と、排気温度及び外気温度に基づき推定される。ここでは、排気温度が高いほど、排気通路４０の壁面が排気から受ける熱量が増加すると考えられることから、内壁温度を高く推定する。また、外気温度が低いほど、排気通路４０の壁面から外部へと流出する熱量が増加すると考えられることから、内壁温度を低く推定する。更に、車速が大きいほど、排気通路４０壁面に吹き付けられる外気の流量が増加すると考えられることから、内壁温度を低く推定する。この推定は、排気通路４０の壁面の比熱等に基づき、例えば熱の授受に関するモデルを用いて行えばよい。なお、上記外気温度として、本実施形態では、吸気温センサ１６にて検出される吸気温度を用いる。   The temperature of the inner wall of the exhaust passage 40 is estimated based on the vehicle speed detected by the vehicle speed sensor 84, the exhaust temperature, and the outside air temperature. Here, it is considered that the higher the exhaust gas temperature is, the more heat the wall surface of the exhaust passage 40 receives from the exhaust gas, so the inner wall temperature is estimated to be higher. Moreover, since it is thought that the amount of heat flowing out from the wall surface of the exhaust passage 40 to the outside increases as the outside air temperature decreases, the inner wall temperature is estimated to be low. Furthermore, since it is considered that the flow rate of the outside air blown to the wall surface of the exhaust passage 40 increases as the vehicle speed increases, the inner wall temperature is estimated to be low. This estimation may be performed using, for example, a model related to heat transfer based on the specific heat of the wall surface of the exhaust passage 40 or the like. As the outside air temperature, in the present embodiment, the intake air temperature detected by the intake air temperature sensor 16 is used.

続くステップＳ１４においては、加速中であるか否かを判断する。ここでは、実際にはアクセルセンサ８２の検出値等に基づき、ディーゼル機関１０の要求トルクの増大時であるか否かを判断する。そして、要求トルクの増大時であると判断される場合、ステップＳ１６において、先の図６に示した態様にて、昇温制御を行う。   In a succeeding step S14, it is determined whether or not acceleration is being performed. Here, based on the detection value of the accelerator sensor 82 or the like, it is determined whether or not the required torque of the diesel engine 10 is actually increasing. If it is determined that the required torque is increasing, in step S16, the temperature rise control is performed in the manner shown in FIG.

これに対し、上記ステップＳ１４において否定判断される場合、ステップＳ１８において、アイドリング状態であるか否かを判断する。この処理は、アイドリング時には、上記ステップＳ１２の処理とは別の手法にて推定される尿素析出物堆積量に基づき、尿素水添加量低減制御や昇温制御を行うことに鑑みて設けられるものである。   On the other hand, if a negative determination is made in step S14, it is determined in step S18 whether or not the vehicle is in an idling state. This process is provided in view of performing urea water addition amount reduction control and temperature increase control based on the urea deposit accumulation amount estimated by a method different from the process of step S12 during idling. is there.

上記ステップＳ１８においてアイドリング時でないと判断される場合、ステップＳ２０において、先の図５に示した排気温の昇温制御中であるか否かを判断する。そして、ステップＳ２０において否定判断される場合、ステップＳ２２に移行する。ステップＳ２２のいては、上記ステップＳ１２の処理によって推定された堆積量が閾値α以上であるか否かを判断する。この処理は、先の図５に示した昇温制御を実行するか否かを判断するためのものである。ステップＳ２２において否定判断される場合、ステップＳ２４において、上記ステップＳ１２の処理によって推定された堆積量が閾値β以上であるか否かを判断する。ここで、閾値βは、上記閾値αよりも小さい値に設定されている。この処理は、先の図４に示した尿素水添加量の低減制御を実行するか否かを判断するためのものである。そして、ステップＳ２４において肯定判断される場合、ステップＳ２６において、排気温が閾値温度γ以下であるか否かを判断する。この処理も、先の図４に示した尿素水添加量の低減制御を実行するか否かを判断するためのものである。そして、ステップＳ２６において肯定判断される場合、ステップＳ２８において、先の図４に示した態様にて尿素水添加量の低減制御を実行する。   If it is determined in step S18 that it is not idling, it is determined in step S20 whether the exhaust gas temperature raising control shown in FIG. 5 is being performed. If a negative determination is made in step S20, the process proceeds to step S22. In step S22, it is determined whether or not the deposition amount estimated by the process in step S12 is equal to or greater than the threshold value α. This process is for determining whether or not to execute the temperature raising control shown in FIG. When a negative determination is made in step S22, it is determined in step S24 whether or not the accumulation amount estimated by the process in step S12 is equal to or greater than the threshold value β. Here, the threshold value β is set to a value smaller than the threshold value α. This process is for determining whether or not to execute the urea water addition amount reduction control shown in FIG. If an affirmative determination is made in step S24, it is determined in step S26 whether or not the exhaust temperature is equal to or lower than a threshold temperature γ. This process is also for determining whether or not to execute the urea water addition amount reduction control shown in FIG. If an affirmative determination is made in step S26, urea water addition amount reduction control is executed in step S28 in the manner shown in FIG.

これに対し、上記ステップＳ２２において肯定判断される場合には、ステップＳ３０において、先の図５に示した昇温制御を実行する。そして、ステップＳ３０の処理が完了する場合や、ステップＳ２０において肯定判断される場合には、ステップＳ３２に移行する。ステップＳ３２においては、先の図５に示したように、昇温制御を踏まえて尿素水添加量を低減する処理を行う。詳しくは、上記ステップＳ１２において推定される堆積量に基づき、昇温制御によって析出物が分解することに起因したアンモニアの発生量に応じて、尿素水添加弁６２から添加される尿素水の量を低減させる。こうした処理を簡易に行ううえでは、上記ステップＳ１２において推定対象となる堆積量は、析出物が分解された場合のアンモニアの発生量として定量化されることが望ましい。   In contrast, if an affirmative determination is made in step S22, the temperature increase control shown in FIG. 5 is executed in step S30. Then, when the process of step S30 is completed or when an affirmative determination is made in step S20, the process proceeds to step S32. In step S32, as shown in FIG. 5, the process of reducing the urea water addition amount is performed based on the temperature rise control. Specifically, based on the amount of deposition estimated in step S12, the amount of urea water added from the urea water addition valve 62 is determined according to the amount of ammonia generated due to the decomposition of precipitates by temperature increase control. Reduce. In order to perform such processing easily, it is desirable that the amount of deposition to be estimated in step S12 is quantified as the amount of ammonia generated when the precipitate is decomposed.

ステップＳ３２の処理が完了する場合、ステップＳ３４に移行する。ここでは、上記ステップＳ１２において推定された堆積量が閾値ε以下であるか否かを判断する。この処理は、昇温制御を停止するか否かを判断するためのものである。ここで、閾値εは、閾値βよりも大きい値に設定されている。そして、ステップＳ３４において肯定判断される場合、ステップＳ３６において、昇温制御を停止するとともに、上記ステップＳ３２の処理を停止し、通常の尿素水の添加制御に戻る。   When the process of step S32 is completed, the process proceeds to step S34. Here, it is determined whether or not the deposition amount estimated in step S12 is equal to or less than the threshold value ε. This process is for determining whether or not to stop the temperature increase control. Here, the threshold value ε is set to a value larger than the threshold value β. If an affirmative determination is made in step S34, the temperature rise control is stopped in step S36, the process in step S32 is stopped, and the process returns to normal urea water addition control.

一方、上記ステップＳ１８において肯定判断される場合には、ステップＳ３８において、アイドリング時間をカウントする。ここで、アイドリング時間は、排気通路４０内壁への析出物の堆積量を定量化するためのパラメータである。続くステップＳ４０においては、アイドリング時間が閾値時間Ｔ１より長いか否かを判断する。この処理は、先の図５に示した昇温制御を実行するか否かを判断するためのものである。ここで、閾値時間Ｔ１は、排気通路４０内壁への析出物の堆積量が上記閾値α程度となると想定される時間に設定されている。   On the other hand, if a positive determination is made in step S18, the idling time is counted in step S38. Here, the idling time is a parameter for quantifying the amount of deposits deposited on the inner wall of the exhaust passage 40. In a succeeding step S40, it is determined whether or not the idling time is longer than the threshold time T1. This process is for determining whether or not to execute the temperature raising control shown in FIG. Here, the threshold time T1 is set to a time when the amount of deposits deposited on the inner wall of the exhaust passage 40 is assumed to be about the threshold value α.

上記ステップＳ４０において否定判断される場合、昇温制御を行うほどには堆積量が多くはないと判断し、ステップＳ４２に移行する。ステップＳ４２においては、アイドリング時間が閾値時間Ｔ０よりも長いか否かを判断する。この処理は、尿素水添加量の低減制御を実行するか否かを判断するためのものである。ここで、閾値時間Ｔ０は、排気通路４０内壁への析出物の堆積量が上記閾値β程度となると想定される時間に設定されている。そして、ステップＳ４２において肯定判断される場合、ステップＳ４４において、尿素水添加量の低減制御を実行する。   When a negative determination is made in step S40, it is determined that the accumulation amount is not so large as to perform the temperature increase control, and the process proceeds to step S42. In step S42, it is determined whether the idling time is longer than the threshold time T0. This process is for determining whether or not to execute the urea water addition amount reduction control. Here, the threshold time T0 is set to a time when the amount of deposits deposited on the inner wall of the exhaust passage 40 is assumed to be about the threshold β. If an affirmative determination is made in step S42, urea water addition amount reduction control is executed in step S44.

これに対し、上記ステップＳ４０において肯定判断される場合、ステップＳ４６において、昇温制御を実行する。続くステップＳ４８においては、上記ステップＳ３２と同様の処理を行う。そして、ステップＳ５０においては、昇温制御時間が閾値時間Ｔ２以上であるか否かを判断する。この処理は、昇温制御を停止するか否かを判断するためのものである。ここで、閾値時間Ｔ２は、排気通路４０内壁への析出物の堆積量が昇温制御によって上記閾値ε程度まで減少すると想定される時間に設定されている。そして、ステップＳ５０において肯定判断される場合、ステップＳ５２において、昇温制御を停止するとともに、上記ステップＳ４８の処理を停止し、通常の尿素水の添加制御に戻り、更にアイドリング時間を初期化する。   On the other hand, when an affirmative determination is made in step S40, the temperature increase control is executed in step S46. In the subsequent step S48, processing similar to that in step S32 is performed. In step S50, it is determined whether or not the temperature increase control time is equal to or longer than the threshold time T2. This process is for determining whether or not to stop the temperature increase control. Here, the threshold time T2 is set to a time during which the amount of deposits deposited on the inner wall of the exhaust passage 40 is assumed to decrease to about the threshold value ε by the temperature increase control. If an affirmative determination is made in step S50, the temperature increase control is stopped in step S52, the processing in step S48 is stopped, the process returns to normal urea water addition control, and the idling time is further initialized.

なお、上記ステップＳ１０，Ｓ２４，Ｓ２６，Ｓ３４，Ｓ４２，Ｓ５０において否定判断される場合や、ステップＳ１６，Ｓ２８，Ｓ３６，Ｓ４４，Ｓ５２の処理が完了する場合には、この一連の処理を一旦終了する。   When a negative determination is made in steps S10, S24, S26, S34, S42, and S50, or when the processes in steps S16, S28, S36, S44, and S52 are completed, the series of processes is temporarily terminated. .

以上詳述した本実施形態によれば、以下の効果が得られるようになる。   According to the embodiment described in detail above, the following effects can be obtained.

（１）推定される堆積量が規定値以上となる場合に、尿素水添加量を強制的に低減した。これにより、排気通路４０内壁への析出物の堆積を好適に抑制することができる。   (1) The amount of urea water added was forcibly reduced when the estimated accumulation amount was equal to or greater than a specified value. Thereby, the deposit of the deposit on the inner wall of the exhaust passage 40 can be suitably suppressed.

（２）推定される堆積量が所定値以上となる場合、ディーゼル機関１０の排気温度を、析出物を除去可能な温度までステップ状に上昇させた。これにより、排気通路４０内壁の堆積量が過度に多くなることを好適に抑制することができる。   (2) When the estimated accumulation amount is equal to or greater than a predetermined value, the exhaust temperature of the diesel engine 10 is increased stepwise to a temperature at which precipitates can be removed. Thereby, it can suppress suitably that the accumulation amount of the inner wall of the exhaust passage 40 increases excessively.

（３）堆積量が所定以下となったと判断される場合、排気温度の上昇処理を停止した。これにより、燃料消費量が増加することを極力抑制することができる。   (3) When it is determined that the accumulation amount is equal to or less than the predetermined amount, the exhaust temperature increasing process is stopped. Thereby, it can suppress that a fuel consumption increases.

（４）ディーゼル機関１０に対する要求トルクの増大時、ディーゼル機関１０の排気温度を、析出物を除去可能な温度までステップ状に上昇させた。これにより、析出物の各成分が分解を開始する温度の相違によって尿素ＳＣＲ５２へのアンモニア供給量の把握精度が低下することを好適に抑制することができる。   (4) When the required torque for the diesel engine 10 is increased, the exhaust temperature of the diesel engine 10 is increased stepwise to a temperature at which precipitates can be removed. Thereby, it can suppress suitably that the grasping precision of the ammonia supply amount to urea SCR52 falls by the difference in the temperature which each component of a precipitate starts decomposition.

（５）昇温制御がなされる場合、尿素水添加弁６２による尿素水の添加量を低減した。これにより、析出物の分解に起因した尿素ＳＣＲ５２へのアンモニア供給量の増加を好適に補償することができ、ひいては尿素ＳＣＲ５２に所望の量のアンモニアを供給することができる。   (5) When temperature increase control is performed, the amount of urea water added by the urea water addition valve 62 is reduced. As a result, an increase in the amount of ammonia supplied to the urea SCR 52 due to the decomposition of the precipitate can be suitably compensated, and as a result, a desired amount of ammonia can be supplied to the urea SCR 52.

（６）ディーゼル機関１０の排気系の温度と相関を有するパラメータ(排気温度)及び添加量に基づき、堆積量を推定した。これにより、堆積量を適切に推定することができる。   (6) The deposition amount was estimated based on the parameter (exhaust temperature) correlated with the temperature of the exhaust system of the diesel engine 10 and the addition amount. Thereby, the amount of deposition can be estimated appropriately.

（７）堆積量の推定に際し、車両の走行速度及び外気温度を加味した。これにより、排気通路４０から外部への熱の拡散態様を高精度に把握することができるため、排気通路４０の内壁温度を高精度に把握することができ、ひいては堆積量を高精度に推定することができる。   (7) In estimating the accumulation amount, the traveling speed of the vehicle and the outside air temperature were taken into account. Thereby, since the diffusion mode of the heat from the exhaust passage 40 to the outside can be grasped with high accuracy, the inner wall temperature of the exhaust passage 40 can be grasped with high accuracy, and as a result, the accumulation amount is estimated with high accuracy. be able to.

（８）ディーゼル機関１０のアイドル運転時、当該アイドル運転のなされる時間に基づき堆積量を推定した。これにより、アイドリング時間を堆積量と相関を有するパラメータとして利用することで堆積量を好適に推定することができる。   (8) During the idling operation of the diesel engine 10, the amount of deposition was estimated based on the time during which the idling operation was performed. Thereby, the deposition amount can be suitably estimated by using the idling time as a parameter having a correlation with the deposition amount.

（第２の実施形態）
以下、第２の実施形態について、先の第１の実施形態との相違点を中心に図面を参照しつつ説明する。 (Second Embodiment)
Hereinafter, the second embodiment will be described with reference to the drawings with a focus on differences from the first embodiment.

本実施形態では、尿素水添加弁６２によって添加される尿素水の添加量を、ＮＯｘ浄化率に基づき算出する。ここで、ＮＯｘ浄化率は、上流側ＮＯｘセンサ５６と下流側ＮＯｘセンサ６０との双方の検出値に基づき算出される。   In the present embodiment, the amount of urea water added by the urea water addition valve 62 is calculated based on the NOx purification rate. Here, the NOx purification rate is calculated based on detection values of both the upstream NOx sensor 56 and the downstream NOx sensor 60.

図８に、本実施形態にかかる窒素酸化物の浄化処理の手順を示す。この処理は、ＥＣＵ８０によって、例えば所定周期で繰り返し実行される。なお、図８において、先の図７に示した処理に対応する処理については、便宜上同一のステップ番号を付している。   FIG. 8 shows the procedure of the nitrogen oxide purifying process according to this embodiment. This process is repeatedly executed by the ECU 80, for example, at a predetermined cycle. In FIG. 8, processes corresponding to the processes shown in FIG. 7 are given the same step numbers for convenience.

図示されるように、本実施形態では、アイドリング運転時でない場合の尿素水添加量の低減制御の実行条件として、堆積量が閾値β以上との条件に代えて、堆積量の増加速度が閾値速度Ｓｔｈ以上であるとの条件を用いる（ステップＳ２４ａ）。これにより、排気通路４０内壁への析出物の堆積量が過度に大きくなることを確実に回避する。ここで、堆積量の増加速度が非常に大きい状況にあっては、排気中のＮＯｘ濃度が低下する。このため、尿素水添加量の低減制御を行ったとしても、ＮＯｘ浄化率が低下することはない。   As shown in the drawing, in the present embodiment, as an execution condition for the urea water addition amount reduction control when the idling operation is not being performed, instead of the condition that the accumulation amount is equal to or greater than the threshold value β, the increase rate of the accumulation amount is the threshold velocity. The condition that it is greater than or equal to Sth is used (step S24a). This reliably avoids an excessive increase in the amount of deposits deposited on the inner wall of the exhaust passage 40. Here, in a situation where the increase rate of the accumulation amount is very large, the NOx concentration in the exhaust gas decreases. For this reason, even if the reduction control of the urea water addition amount is performed, the NOx purification rate does not decrease.

ここで、本実施形態では、尿素水添加量を、ＮＯｘ浄化率に基づき設定している。このため、排気中のＮＯｘ濃度が低下する状況下であっても、そのことが、設定される尿素水添加量の低減に直接つながるわけではない。このため、本実施形態のように、堆積量の増加速度が大きいときに尿素水添加量を低減する処理を行うことが特に有効となる。   Here, in this embodiment, the urea water addition amount is set based on the NOx purification rate. For this reason, even in a situation where the NOx concentration in the exhaust gas decreases, this does not directly lead to a reduction in the urea water addition amount that is set. For this reason, as in the present embodiment, it is particularly effective to perform a process of reducing the urea water addition amount when the rate of increase in the accumulation amount is large.

（その他の実施形態）
なお、上記各実施形態は、以下のように変更して実施してもよい。 (Other embodiments)
Each of the above embodiments may be modified as follows.

・上記各実施形態では、排気温センサ５８を備えて排気温度を検出したが、これに限らず、ディーゼル機関１０の運転状態を示すパラメータを入力として、排気温度を推定するようにしてもよい。こうしたパラメータとしては、例えば燃料噴射量や回転速度等がある。   In each of the above embodiments, the exhaust gas temperature sensor 58 is provided to detect the exhaust gas temperature. However, the present invention is not limited to this, and the exhaust gas temperature may be estimated using a parameter indicating the operating state of the diesel engine 10 as an input. Examples of such parameters include a fuel injection amount and a rotational speed.

・上記第２の実施形態において、尿素水添加量の低減制御の開始条件として、堆積量の増加速度が閾値速度Ｓｔｈ以上であるとの条件に加えて、堆積量が閾値β以上であるとの条件が成立することとしてもよい。   In the second embodiment, as the starting condition for the urea water addition amount reduction control, in addition to the condition that the increase rate of the deposition amount is equal to or greater than the threshold velocity Sth, the deposition amount is equal to or greater than the threshold β. The condition may be satisfied.

・上記第１の実施形態においては、排気中のＮＯｘ濃度に基づき尿素水添加量を設定したがこれに限らない。例えば、上記第２の実施形態によるように、尿素ＳＣＲ５２におけるＮＯｘ浄化率に基づき尿素水添加量を設定してもよい。また例えば、尿素ＳＣＲ５２におけるアンモニア吸着量を推定する手段を有し、この推定される吸着量に基づき尿素水添加量を設定してもよい。   In the first embodiment, the urea water addition amount is set based on the NOx concentration in the exhaust gas, but the present invention is not limited to this. For example, as in the second embodiment, the urea water addition amount may be set based on the NOx purification rate in the urea SCR 52. Further, for example, a means for estimating the ammonia adsorption amount in the urea SCR 52 may be provided, and the urea water addition amount may be set based on the estimated adsorption amount.

・上記第２の実施形態では、尿素ＳＣＲ５２におけるＮＯｘ浄化率に基づき尿素水添加量を設定したがこれに限らない。例えば、尿素ＳＣＲ５２におけるアンモニア吸着量を推定する手段を有し、この推定される吸着量に基づき尿素水添加量を設定してもよい。また、例えば、上記第１の実施形態によるように、排気中のＮＯｘ濃度に基づき尿素水添加量を設定してもよい。   In the second embodiment, the urea water addition amount is set based on the NOx purification rate in the urea SCR 52, but the present invention is not limited to this. For example, a means for estimating the ammonia adsorption amount in the urea SCR 52 may be provided, and the urea water addition amount may be set based on the estimated adsorption amount. Further, for example, as in the first embodiment, the urea water addition amount may be set based on the NOx concentration in the exhaust gas.

なお、上述したように、堆積量の増加速度が閾値速度Ｓｔｈ以上である場合とは、排気温度が低く、排気中のＮＯｘ濃度が低い状況であると考えられる。しかし、尿素水添加量をＮＯｘ浄化率や尿素ＳＣＲ５２内のアンモニア吸着量に基づき設定する場合には、尿素水添加量を排気中のＮＯｘ濃度に基づき設定する場合と比較して、尿素水添加量の低減が遅れるおそれがある。このため、ディーゼル機関１０の燃焼室２８から排出される排気のＮＯｘ濃度を尿素水添加量の推定に際しての直接の入力パラメータとしない設定の場合には、堆積量の増加速度が閾値速度Ｓｔｈ以上である場合に尿素添加量の低減制御を行うことは、尿素添加量の低減制御を迅速に行ううえで特に有効である。   As described above, the case where the increase rate of the accumulation amount is equal to or higher than the threshold speed Sth is considered to be a situation where the exhaust gas temperature is low and the NOx concentration in the exhaust gas is low. However, when the urea water addition amount is set based on the NOx purification rate or the ammonia adsorption amount in the urea SCR 52, the urea water addition amount is compared with the case where the urea water addition amount is set based on the NOx concentration in the exhaust gas. May be delayed. For this reason, when the NOx concentration of the exhaust gas discharged from the combustion chamber 28 of the diesel engine 10 is set not to be a direct input parameter when estimating the urea water addition amount, the increase rate of the accumulation amount is equal to or higher than the threshold speed Sth. In some cases, the urea addition amount reduction control is particularly effective in quickly performing the urea addition amount reduction control.

・上記各実施形態では、アイドリング運転以外の運転領域において、堆積量が閾値β以上であるとの条件と排気温度が閾値温度γ以下であるとの条件との論理積条件が成立する場合に、尿素水添加量の低減制御を行ったが、これに限らない。例えば、堆積量が閾値β以上であるとの条件が成立する場合に排気温度にかかわらず尿素水添加量の低減制御を行ってもよい。   In each of the above embodiments, in the operation region other than the idling operation, when a logical product condition of the condition that the accumulation amount is equal to or higher than the threshold value β and the condition that the exhaust gas temperature is equal to or lower than the threshold temperature γ is satisfied, Although the reduction control of the urea water addition amount is performed, the present invention is not limited to this. For example, when the condition that the accumulation amount is equal to or greater than the threshold value β is satisfied, the urea water addition amount reduction control may be performed regardless of the exhaust gas temperature.

・上記各実施形態では、アイドリング運転以外の運転領域における昇温制御の停止の判断のための閾値εを、尿素水添加量の低減制御の開始の判断のための閾値βよりも大きく設定したがこれに限らない。例えば、閾値εを閾値β以下に設定してもよい。これによれば、ディーゼル機関１０に対する要求トルクの増大時以前であっても排気通路４０の内壁面の析出物堆積量を十分に低減することができる。   In each of the above embodiments, the threshold value ε for determining whether to stop the temperature increase control in the operation region other than the idling operation is set larger than the threshold value β for determining the start of the urea water addition amount reduction control. Not limited to this. For example, the threshold value ε may be set to be equal to or less than the threshold value β. According to this, the deposit amount on the inner wall surface of the exhaust passage 40 can be sufficiently reduced even before the increase in the required torque for the diesel engine 10.

・上記各実施形態では、アイドリング時においては、尿素熱分解生成物の堆積量の推定値として、アイドリング時間を用いたがこれに限らない。例えばアイドリング時においても、排気系の温度と相関を有するパラメータ及び尿素水添加量に基づき推定される堆積量を用いてもよい。また、排気系の温度と相関を有するパラメータ及び尿素水添加量に基づき堆積量を推定するものにおいて、アイドリング時には、上記パラメータ及び尿素水添加量に代えてアイドリング時間に応じて堆積量を増加推定するようにしてもよい。こうした変更を行うなら、アイドリング時である場合とない場合とで、排気温度の昇温制御の実行条件や添加量低減制御の実行条件を同一とすることができる。   In each of the above-described embodiments, the idling time is used as the estimated value of the amount of deposited urea pyrolysis product at the time of idling, but is not limited thereto. For example, at the time of idling, a deposition amount estimated based on a parameter having a correlation with the temperature of the exhaust system and the urea water addition amount may be used. In addition, in the case of estimating the amount of deposition based on a parameter correlated with the temperature of the exhaust system and the amount of urea water added, at the time of idling, the amount of deposition is estimated to increase according to the idling time instead of the parameter and the amount of urea water added You may do it. If such a change is made, the execution condition of the exhaust gas temperature increase control and the execution condition of the addition amount reduction control can be made the same in the case of idling and not.

・析出物の堆積量の推定手段としては、上記各実施形態及びこれらの変形例にて例示したものに限らない。例えばアイドリング時において、アイドリング時間と、排気系の温度と相関を有するパラメータ及び尿素添加量の少なくとも一方とに基づき各推定処理周期における堆積量の推定処理を行ってもよい。   The means for estimating the deposit amount is not limited to those exemplified in the above embodiments and their modifications. For example, during idling, the accumulation amount estimation processing in each estimation processing cycle may be performed based on the idling time and at least one of a parameter correlated with the exhaust system temperature and the urea addition amount.

・上記各実施形態では、アイドリング運転以外の運転領域において、析出物の堆積量の推定値が閾値β以下となる場合に排気温度の昇温制御を停止したがこれに限らない。例えば昇温制御時間が所定時間となることを条件としてもよい。この場合、昇温制御時間が、析出物の堆積量を示すパラメータとなっている。すなわち、昇温制御時間が長いほど、堆積量が少ないことを意味する。   In each of the embodiments described above, the temperature increase control of the exhaust gas temperature is stopped when the estimated value of the deposit amount is equal to or less than the threshold value β in the operation region other than the idling operation. For example, the temperature increase control time may be a predetermined time. In this case, the temperature rise control time is a parameter indicating the amount of deposits deposited. That is, the longer the temperature rise control time, the smaller the deposition amount.

・上記各実施形態では、アイドリング運転領域において、昇温制御時間が閾値時間Ｔ２となる場合に排気温度の昇温制御を停止したがこれに限らない。例えば析出物の堆積量の推定値が閾値β以下となる場合に昇温制御を停止してもよい。   In each of the above embodiments, the exhaust gas temperature increase control is stopped when the temperature increase control time reaches the threshold time T2 in the idling operation region, but the present invention is not limited to this. For example, the temperature rise control may be stopped when the estimated value of the deposit amount is equal to or less than the threshold value β.

・排気温度を上昇させるべく行われる排気通路４０への燃料の供給処理としては、ポスト噴射を行うものに限らない。例えば排気通路４０に燃料を噴射する燃料噴射弁を別途備えるものにあっては、これによって排気通路４０に燃料を噴射する処理とすればよい。   The fuel supply process to the exhaust passage 40 performed to increase the exhaust temperature is not limited to the one that performs post injection. For example, in the case of separately providing a fuel injection valve for injecting fuel into the exhaust passage 40, the process for injecting fuel into the exhaust passage 40 may be performed.

・排気温度を上昇させるべく用いられる変速装置としては、上記ＣＶＴ３５に限らない。例えば有段変速装置であってもよい。   The transmission used to raise the exhaust temperature is not limited to the CVT 35. For example, it may be a stepped transmission.

・排気温度を上昇させる制御としては、排気温度を「３００°Ｃ」程度とするものに限らない。例えば「３００°Ｃ」よりも高い温度とするものであってもよい。この場合、排気通路４０の堆積物が一気に分解してアンモニアとなると考えられるため、尿素ＳＣＲ５２へのアンモニア供給量の予測がいっそう容易となると考えられる。   The control for raising the exhaust temperature is not limited to the exhaust temperature set to about “300 ° C.”. For example, the temperature may be higher than “300 ° C.”. In this case, it is considered that the deposit in the exhaust passage 40 is decomposed at a stretch into ammonia, so that it is considered that the ammonia supply amount to the urea SCR 52 can be predicted more easily.

・排気中の窒素酸化物を浄化する浄化手段としては、上記尿素ＳＣＲ５２に限らない。例えば、上流側の排気中に尿素水以外の還元剤が添加される選択還元型触媒としてもよい。この場合であっても、排気通路４０の内壁面温度が低い場合に還元剤に起因して、分解開始温度の相違する複数の成分を有する析出物が堆積されるおそれがあるなら、本発明の適用が有効である。なお、この際、排気温度の上昇処理は、析出物の各成分が分解を開始する温度の最大値以上に設定することが望ましい。   -Purifying means for purifying nitrogen oxide in the exhaust is not limited to the urea SCR 52. For example, a selective reduction catalyst in which a reducing agent other than urea water is added to the exhaust on the upstream side may be used. Even in this case, if the inner wall surface temperature of the exhaust passage 40 is low, there is a risk that deposits having a plurality of components having different decomposition start temperatures may be deposited due to the reducing agent. Application is effective. At this time, it is desirable to set the exhaust temperature increasing process to be equal to or higher than the maximum temperature at which each component of the precipitate starts to decompose.

・内燃機関としては、ディーゼル機関のような圧縮着火式内燃機関に限らない。例えば筒内噴射式ガソリン機関等の火花点火式内燃機関にあっても、ＮＯｘの浄化に選択還元型触媒を用いる場合には、本発明の適用は有効である。   -The internal combustion engine is not limited to a compression ignition type internal combustion engine such as a diesel engine. For example, even in a spark ignition type internal combustion engine such as an in-cylinder injection type gasoline engine, the application of the present invention is effective when a selective reduction catalyst is used for NOx purification.

第１の実施形態にかかるシステム構成図。1 is a system configuration diagram according to a first embodiment. FIG. 同実施形態にかかる尿素熱分解生成物の融点を示す図。The figure which shows melting | fusing point of the urea thermal decomposition product concerning the embodiment. 同実施形態にかかる尿素熱分解生成物の経時変化の計測結果を示す図。The figure which shows the measurement result of the time-dependent change of the urea thermal decomposition product concerning the embodiment. 同実施形態にかかる尿素水添加量の低減制御態様を示すタイムチャート。The time chart which shows the reduction | decrease control aspect of the urea water addition amount concerning the embodiment. 同実施形態にかかる排気温度の上昇処理態様を示すタイムチャート。The time chart which shows the rise process aspect of the exhaust temperature concerning the embodiment. 同実施形態にかかる要求トルクの増大時における排気温度の上昇処理態様を示すタイムチャート。The time chart which shows the rise process mode of exhaust temperature at the time of the increase in the request torque concerning the embodiment. 同実施形態にかかる排気浄化制御の処理手順を示す流れ図。The flowchart which shows the process sequence of the exhaust gas purification control concerning the embodiment. 第２の実施形態にかかる排気浄化制御の処理手順を示す流れ図。The flowchart which shows the process sequence of the exhaust gas purification control concerning 2nd Embodiment.

符号の説明Explanation of symbols

１０…ディーゼル機関、４０…排気通路、５２…尿素ＳＣＲ（浄化手段の一実施形態）、６２…尿素水添加弁、８０…ＥＣＵ（排気浄化装置の一実施形態）。   DESCRIPTION OF SYMBOLS 10 ... Diesel engine, 40 ... Exhaust passage, 52 ... Urea SCR (one embodiment of purification means), 62 ... Urea water addition valve, 80 ... ECU (one embodiment of exhaust purification device)

Claims (11)

内燃機関の排気通路に設けられて且つ排気中の窒素酸化物を浄化する浄化手段と、前記浄化手段の上流側の排気中に還元剤を添加する添加手段とを備える排気浄化装置に適用され、前記添加手段の操作に基づき前記還元剤の添加量を調節しつつ前記浄化手段による窒素酸化物の浄化制御を行う内燃機関の排気浄化制御装置において、
前記還元剤の添加に起因した前記排気通路内壁への析出物の堆積量を推定する推定手段と、
前記推定される堆積量が規定値以上となること及び前記堆積量の増加速度が規定速度以上となることの少なくとも一方が成立する場合、前記還元剤の添加量を強制的に低減する低減手段とを備えることを特徴とする内燃機関の排気浄化制御装置。 Applied to an exhaust gas purification device provided with a purification means that is provided in an exhaust passage of an internal combustion engine and purifies nitrogen oxides in exhaust gas, and an addition means that adds a reducing agent to the exhaust gas upstream of the purification means, In an exhaust gas purification control device for an internal combustion engine that performs purification control of nitrogen oxides by the purification means while adjusting the amount of addition of the reducing agent based on the operation of the addition means,
Estimating means for estimating the amount of deposits deposited on the inner wall of the exhaust passage due to the addition of the reducing agent;
A reduction means for forcibly reducing the addition amount of the reducing agent when at least one of the estimated accumulation amount is equal to or greater than a specified value and the increase rate of the accumulation amount is equal to or greater than a specified rate; An exhaust gas purification control apparatus for an internal combustion engine, comprising: 前記推定される堆積量が所定値以上となる場合、前記内燃機関の排気温度を、前記析出物を除去可能な温度まで上昇させる排気温度上昇手段を更に備えることを特徴とする請求項１記載の内燃機関の排気浄化制御装置。   The exhaust gas temperature raising means for raising the exhaust temperature of the internal combustion engine to a temperature at which the deposits can be removed when the estimated accumulation amount is a predetermined value or more. An exhaust purification control device for an internal combustion engine. 前記堆積量が所定以下となったと判断される場合、前記排気温度の上昇処理を停止することを特徴とする請求項２記載の内燃機関の排気浄化制御装置。   3. The exhaust gas purification control apparatus for an internal combustion engine according to claim 2, wherein when it is determined that the accumulation amount has become equal to or less than a predetermined value, the exhaust gas temperature increasing process is stopped. 前記内燃機関に対する要求トルクの増大時である場合、前記内燃機関の排気温度を、前記析出物を除去可能な温度まで前記内燃機関のトルクの増大に伴う上昇速度よりも急激に上昇させるトルク増大時上昇手段を更に備えることを特徴とする請求項１記載の内燃機関の排気浄化制御装置。   When the required torque for the internal combustion engine increases, when the torque increases to increase the exhaust temperature of the internal combustion engine to a temperature at which the deposits can be removed more rapidly than the increase speed associated with the increase in torque of the internal combustion engine 2. The exhaust gas purification control apparatus for an internal combustion engine according to claim 1, further comprising a raising means. 前記上昇手段による排気温度の上昇処理がなされる場合、前記添加手段による前記還元剤の添加量を低減することを特徴とする請求項２〜４のいずれか１項に記載の内燃機関の排気浄化制御装置。   The exhaust purification of an internal combustion engine according to any one of claims 2 to 4, wherein when the exhaust temperature is increased by the increasing means, the amount of the reducing agent added by the adding means is reduced. Control device. 前記上昇手段は、前記内燃機関の燃料噴射タイミングの遅角処理、前記内燃機関の排気通路への燃料の供給処理、及び前記内燃機関の排気還流量の増加処理の少なくとも１つを行うことを特徴とする請求項２〜５のいずれか１項に記載の内燃機関の排気浄化制御装置。   The raising means performs at least one of processing for retarding the fuel injection timing of the internal combustion engine, processing for supplying fuel to the exhaust passage of the internal combustion engine, and processing for increasing the exhaust gas recirculation amount of the internal combustion engine. An exhaust purification control apparatus for an internal combustion engine according to any one of claims 2 to 5. 前記内燃機関は、車載内燃機関であり、
前記内燃機関の出力軸は、変速装置を介して駆動輪に連結されるものであり、
前記上昇手段は、前記変速装置の変速比を操作することで車両の走行速度の低下を抑制しつつ前記内燃機関の出力軸の回転速度を低下させるものであることを特徴とする請求項２〜６のいずれか１項に記載の内燃機関の排気浄化制御装置。 The internal combustion engine is an in-vehicle internal combustion engine,
The output shaft of the internal combustion engine is connected to drive wheels via a transmission,
The said raising means reduces the rotational speed of the output shaft of the said internal combustion engine, suppressing the fall of the driving speed of a vehicle by operating the gear ratio of the said transmission. The exhaust gas purification control apparatus for an internal combustion engine according to any one of claims 6 to 6. 前記推定手段は、前記内燃機関の排気系の温度と相関を有するパラメータ及び前記添加量に基づき、前記堆積量を推定することを特徴とする請求項１〜７のいずれか１項に記載の内燃機関の排気浄化制御装置。   The internal combustion engine according to claim 1, wherein the estimation unit estimates the accumulation amount based on a parameter having a correlation with a temperature of an exhaust system of the internal combustion engine and the addition amount. Engine exhaust purification control device. 前記推定手段は、前記内燃機関のアイドル運転時、当該アイドル運転のなされる時間に基づき前記堆積量を推定することを特徴とする請求項１〜８のいずれか１項に記載の内燃機関の排気浄化制御装置。   The exhaust of the internal combustion engine according to any one of claims 1 to 8, wherein the estimation means estimates the accumulation amount based on a time during which the internal combustion engine is idle during idle operation. Purification control device. 前記還元剤が尿素水であることを特徴とする請求項１〜９のいずれか１項に記載の内燃機関の排気浄化制御装置。   The exhaust purification control device for an internal combustion engine according to any one of claims 1 to 9, wherein the reducing agent is urea water. 請求項１〜１０のいずれか１項に記載の内燃機関の排気浄化制御装置と、
前記浄化手段とを備えることを特徴とする内燃機関の排気浄化システム。 An exhaust gas purification control device for an internal combustion engine according to any one of claims 1 to 10,
An exhaust gas purification system for an internal combustion engine comprising the purification means.
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