CN102939454B - 废气净化*** - Google Patents

废气净化*** Download PDF

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CN102939454B
CN102939454B CN201180025424.8A CN201180025424A CN102939454B CN 102939454 B CN102939454 B CN 102939454B CN 201180025424 A CN201180025424 A CN 201180025424A CN 102939454 B CN102939454 B CN 102939454B
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automatic regeneration
regeneration
exhaust gas
pid
exhaust
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CN102939454A (zh
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池田卓史
村田哲也
柳沼谦三
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Isuzu Motors Ltd
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    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01NGAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/0807Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents
    • F01N3/0821Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents combined with particulate filters
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D46/00Filters or filtering processes specially modified for separating dispersed particles from gases or vapours
    • B01D46/66Regeneration of the filtering material or filter elements inside the filter
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    • F02D41/024Introducing 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
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    • F02D41/402Multiple injections
    • F02D41/405Multiple injections with post injections
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D2279/00Filters adapted for separating dispersed particles from gases or vapours specially modified for specific uses
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    • F01N3/00Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/02Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust
    • F01N3/021Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters
    • F01N3/033Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters in combination with other devices
    • F01N3/035Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters in combination with other devices with catalytic reactors, e.g. catalysed diesel particulate filters
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    • F01N3/00Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/10Exhaust 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
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Abstract

提供一种废气净化***,能够准确地进行从行驶自动再生到停止时的自动怠速再生的控制,并且即使从自动怠速再生转移至行驶自动再生,废气温度也不会过冲。将捕集废气中的PM的DPD(25)与柴油发动机(10)的排气管(20)连接,在上述DPD(25)的PM量成为一定量以上时,进行后喷射来使柴油发动机(10)的废气温度上升,从而将DPD自动再生,检测自动再生时的DPD再生的废气温度,求出检测的废气温度和再生目标温度的偏差,并基于该偏差PID来对后喷射量进行控制的情况下,在从行驶自动再生转移至停车的怠速自动再生时,将在PID控制中的积分控制项复位为零,从而对后喷射量进行控制。

Description

废气净化***
技术领域
本发明涉及捕集柴油发动机的废气中的PM(Particulate Matter:微粒物质)、同时将NOx净化并排气的废气净化***,尤其涉及在将DPD自动再生时,临时停车并进行怠速自动再生时的废气净化***。
背景技术
作为将柴油发动机的废气净化并排气的废气净化***,开发了将DPD(Diesel Particulate Defuser:柴油机微粒消除器)以及SCR(SelectiveCatalytic Reduction:选择性催化还原)装置与排气管连接的废气净化***。
在该废气净化***中,通过DPD捕集废气中的PM。此外,在废气净化***中,由具备SCR装置的SCR***将贮存在尿素箱中的尿素水供给至SCR的废气上游,通过废气的热生成氨气,通过该氨气在SCR催化剂上将NOx还原而净化(例如参照专利文献1、2)。
由DPD捕集的PM成为过滤器的堵塞的原因,所以需要使捕集堆积的PM适当地氧化,将其除去而再生。
排气压传感器检测DPD前后的差压,在该差压达到上限值时,ECU(Engine Control Unit:发动机控制单元)自动地或手动地进行该堵塞的检测,这种情况下,点亮设置在车舱内的DPD警告灯,驾驶员通过按下再生执行开关,开始DPD再生。
DPD包括由将未燃烧燃料氧化的活性催化剂构成的DOC和捕集废气中的PM的CSF(Catalyzed Soot Filter:催化烟尘过滤器),在DPD再生时,进行燃料的多级喷射(引燃喷射、预喷射、主喷射、延迟喷射),使排气温度上升至DOC的催化剂活性温度以上,然后追加后喷射,使排气温度上升至500℃、600℃左右,通过该高温的废气使由CSF捕集的PM燃烧,将其除去而再生。
在DPD再生中,有在行驶中进行自动再生的情况,和将车停止并以怠速旋转进行手动再生的情况。通常是在行驶中进行自动再生,但由于后喷射而在气筒的润滑油中混入燃料油,产生润滑油的稀释,因而通过手动再生来减少稀释量。
此外,在行驶中的自动再生中,为了在车辆的停止时,即使是怠速旋转也能够进行再生,将排气制动阀关闭来防止排气温度的降低,从而继续进行再生。
该自动再生为,通过设置在DOC的下游侧的排气温度传感器检测流入CSF的废气温度,求出该废气温度和再生目标温度(作为一例,500℃、600℃)的偏差,基于该偏差对后喷射量进行PID控制,以使废气温度成为再生目标温度。
在先技术文献
专利文献
专利文献1:日本特开2000-303826号公报
专利文献2:日本专利第4175281号公报
发明的概要
发明所要解决的技术课题
然而,停车时的怠速自动再生,随着降低至再生怠速转速,将排气制动阀关闭,从即使在转速较低且废气量较少的怠速中,也能够实现DPD内的废气的保温,同时进行后喷射来进行自动再生。
然而,即使如上述那样关闭排气制动阀并进行后喷射,也会由于流入DOC的废气量较少,再生温度未达到再生目标温度的情况较多。此外,后喷射的未燃烧的燃料仍然积蓄在DOC中。
一般来说,PID控制是将比例控制项(P项)、积分控制项(I项)、微分控制项(D项)组合并使其收束至设定值的控制,以如下方式进行控制:通过比例控制项(P项),与偏差成比例地改变操作量,通过积分控制项,将偏差相加,并与该值成比例地改变操作量,从而消除比例控制中的残存偏差(额定偏差),进而在微分控制中,将偏差的变化率转换为速度,并到处与其成比例的操作量,从而加快响应速度,尽早收束至设定值。
在此,在怠速自动再生时,如上述那样,再生温度未达到目标温度,因而,若通过PID控制来控制后喷射量,则在比例控制项中,基于该偏差,输出一定的操作量,此外,微分控制项也没有偏差,所以输出一定的操作量,因而,即使在偏差没有变化的状态下,在怠速控制时,在控制方面也不会导致障碍。但是,在积分控制项中,在规定的积分时间内将偏差求和,所以若怠速控制变长,则积分控制项的操作量增大,上升至上限值。此外,在行驶中和怠速时废气量大为不同,因而,需要各自取得最佳的积分控制项。
像这样,积分控制项上升至上限值并从怠速自动再生变为行驶自动再生的情况下,若打开排气制动阀,并以通过截至目前的PID控制决定的操作量来进行后喷射,则大量的废气从发动机流至DPD,并且积蓄在DOC中的未燃烧的燃料也会燃烧,存在再生温度相对于目标温度过大的过冲(overshoot)的问题。在这种情况下,产生过大的过冲可以认为是在怠速自动再生时间较长的情况下,或者在怠速停止时间较短的情况下,积分控制项的影响较少。
发明内容
在此,本发明的目的在于,解决上述问题,提供一种废气净化***,从行驶自动再生起准确地进行停止时的自动怠速再生的控制,并且即使从自动怠速再生转移至行驶自动再生,废气温度也不会过冲。
解决技术问题所采用的技术手段
为实现上述目的,方案1的发明是一种废气净化***,将捕集废气中的PM的DPD与柴油发动机的排气管连接,在上述DPD的PM量成为一定量以上时,进行后喷射,使柴油发动机的废气温度上升,从而将DPD自动再生,其特征在于,检测自动再生时的DPD再生的废气温度,求出检测的废气温度和再生目标温度的偏差,并基于该偏差对后喷射量进行PID控制的情况下,在从行驶自动再生转移至停车的怠速自动再生时,将PID控制中的积分控制项复位为零,从而对后喷射量进行控制。
方案2的发明是在方案1所述的废气净化***中,从上述停车后的怠速自动再生开始起,在规定时间以内转移至行驶自动再生时,通过上述怠速自动再生将积分控制项复位为零,并通过复位为零后的PID控制直接对后喷射量进行控制。
方案3的发明是在方案1所述的废气净化***中,从上述停车后的怠速自动再生开始起,超过规定时间而转移至行驶自动再生时,再次将PID控制的积分控制项复位为零。
方案4的发明是在方案2或3所述的废气净化***中,上述规定时间为3分钟。
方案5的发明是在方案1所述的废气净化***中,从行驶自动再生将车减速而停车时,在减速时直接通过PID控制来继续后喷射,在停车后将PID控制的积分控制项复位为零。
方案6的发明是在方案1~4的任意一项所述的废气净化***中,在开始怠速自动再生时将排气制动阀关闭,在转移至行驶自动再生时将排气制动器打开。
发明的效果:
根据本发明,具有如下优良效果:能够消除由怠速自动再生时的PID控制导致的不良影响,能够防止在DPD内的废气的过冲。
附图说明
图1是表示本发明的一个实施方式的整体结构图。
图2是表示在本发明中自动再生时的控制图的图。
具体实施方式
以下,基于附图说明本发明的一个优选实施方式。
在图1中,柴油发动机10的进气岐管11和排气岐管12分别与增压机13的压缩机14和涡轮15连结,来自上游侧进气管16a的空气被压缩机14升压,通过下游侧进气管16b的中冷器17而被冷却,并经由进气节流阀18从进气岐管11供给至柴油发动机10,来自柴油发动机10的废气对涡轮15进行驱动,然后排气至排气管20。
在上游侧进气管16a中设置有测定进气量的空气流量传感器(MAF)19,通过该空气流量传感器(MAF)控制进气节流阀18的开度,从而调整进气量。此外,排气管20和上游侧进气管16a连接有用于将废气的一部分返回发动机10的进气***而减少NOx的EGR(Exhaust Gas Recirculation:废气再循环)管21,该EGR管21与EGR冷却器22和EGR阀23连接。
排气管20与排气制动阀24、DPD25、排气节流阀26、***27连接。DPD25包括由将未燃烧燃料氧化的活性催化剂构成的DOC28和捕集废气中的PM的CSF(Catalyzed Soot Filter:催化烟尘过滤器)29。此外,虽未图示,但在排气节流阀26和***27之间连接有SCR装置,通过氨气将NOx脱硝。
在DOC28的前后设置有废气温度传感器30a、30b,并设置有检测CSF29的PM堆积量的差压传感器31,将这些检测值输入至ECU(发动机控制单元)32。
将检测发动机的转速的旋转传感器33的检测值、车速传感器34的检测值、大气压传感器35的检测值输入ECU32。
ECU32在行驶中根据加速踏板开度控制燃料喷射器38中的燃料喷射量,并且适当地控制进气节流阀18、排气制动阀24、排气节流阀26。
在该废气处理***中,ECU32根据检测CSF29的前后的差压的差压传感器31的检测值而判断为在DPD25中PM已经堆积一定量时,或者在从前一次再生后开始的行驶距离达到规定值时,将来自柴油发动机10的废气温度最终升温至600℃左右来使PM燃烧,从而进行再生。
该再生为,为了将废气温度变成DOC28的催化剂活性温度以上,由燃料喷射器38进行多级喷射(引燃喷射、预喷射、主喷射、延迟喷射),然后进行后喷射,使废气温度升温至例如500℃、600℃来使PM燃烧,虽然通常是在行驶中进行自动再生,但由于后喷射而在气筒的润滑油中混入燃料油,产生润滑油的稀释(稀释),因而通过手动再生来减少稀释量。
接下来,通过图2说明自动再生时的ECU32的控制图。
在进行自动再生时,ECU32收束进气节流阀18,关闭EGR阀23,并进行多级喷射来将废气温度升温至催化剂活性温度以上,从而升高DOC28的催化剂的温度,接下来,在多级喷射中加上后喷射,将废气温度升温至例如500℃、600℃来使PM燃烧,从而将DPD25再生。再生完成后,将进气节流阀18和EGR阀23返回至通常控制。
该自动再生中,在车辆由于等待信号等而停车时,将发动机旋转从通常怠速旋转开始,在变速机的齿轮为空挡时使再生怠速转速上升,在齿轮挂档时,为了防止从停止开始行驶时的急起步,将再生怠速转速设定成比齿轮为空挡时的再生怠速转速低。此外,在自动再生中,ECU32点亮自动再生警告灯36b。
在从多级喷射切换至后喷射来将DPD再生时,应该防止废气温度升温至600℃后、堆积的PM一口气燃烧的情况,例如,将初期的再生目标温度设为设为500℃,当DPD内的PM燃烧到某种程度后,改变目标温度,对后喷射量进行控制,以使最终再生目标温度成为例如600℃。
接下来,对后喷射量的PID控制进行说明。
首先,在自动再生中通过由图1说明的废气温度传感器30b检测废气温度,ECU32求出再生目标温度和废气温度的偏差e,并基于该偏差,通过PID控制,决定燃料喷射器38的后喷射的操作量M。
由下式表示该操作量M。
M=Kp·e+Ki·(1/Ti)·∫edt+Kd·Td(de/dt)
上式中,Kp是比例控制的比例常量,Ki是积分控制的比例常量,Kd是微分控制的比例常量,Ti是积分时间,Td是微分时间,t是时间。
在此,操作量M由比例控制项、积分控制项和微分控制项的总和决定。实际的后喷射量是将该操作量M加上基础项的操作量,并由燃料喷射器38的燃油压力和开阀时间决定。
通过该PID控制,在行驶自动再生中,发动机转速也较高,所以能够与后喷射量相应地提高废气温度,因而能够相对于再生目标温度而正确地进行控制。
可是,由于等待信号和交通状况,在车辆停车之前,发动机转速降低,废气量也变少,偏差e变大,在该状态下,车辆停止,通过关闭排气制动阀24和排气节流阀26并增加喷射量,将DPD25内的废气温度控制为不下降,在齿轮为空挡、齿轮挂档的情况下,发动机转速都从通常的怠速转速上升至再生怠速转速,但是在该再生怠速转速下,由于比行驶时的发动机转速低,向发动机的进气量以及废气量也变少,因而维持或者提高再生目标温度变得困难。其结果,偏差e进一步变大。
在此,在偏差e为一定的情况下,虽然比例控制项和微分控制项为一定,但是积分控制项将该增大的偏差e积分,导致在怠速再生中后喷射量上升至上限值。在该控制状态下,在从停止开始行驶并转移至行驶自动再生时,发动机转速上升,并且进气量也增大,废气温度急剧地上升,存在使DPD25熔损的危险。
因此,在本发明中,在车辆停止并开始怠速自动再生时,与排气制动阀24的关闭动作相应地,将PID控制的控制式中的积分控制项复位为零。通过将这样将积分控制项复位为零,不再有停车之前的车的行驶状态的偏差e的积分,并根据停车时的偏差e通过PID控制决定后喷射量,来进行怠速自动再生,从而能够进行稳定的怠速自动再生。
此外,在该复位为零后,在进行怠速自动再生的期间内,在车辆从停车开始行驶规定时间以内(3分钟以内)的情况下,通过基于该复位为零后的PID控制的后喷射量来对行驶自动再生进行控制,能够无障碍地进行行驶自动再生。此外,在停车时间超过3分钟的情况下,由于积分控制项的操作量增大,通过将该积分控制项再次复位为零,来进行行驶自动再生,能够防止废气温度的过冲的产生。
根据以上发明,在怠速自动再生时,在通过PID控制来控制后喷射量时,通过将PID控制的积分控制项复位为零,能够进行稳定的怠速自动再生,此外,在该怠速自动再生后,判断是根据车的停止时间将积分控制项再次复位为零,还是不复位而直接继续控制,从而即使从怠速自动再生转移至行驶自动再生,也能够无障碍地进行该切换。
符号的说明:
10柴油发动机
20排气管
25DPD
32ECU
33旋转传感器
35大气压传感器

Claims (7)

1.一种废气净化***,将捕集废气中的微粒物质的柴油机微粒消除器与柴油发动机的排气管连接,在上述柴油机微粒消除器的微粒物质量成为一定量以上时,进行后喷射,使柴油发动机的废气温度上升,从而将柴油机微粒消除器自动再生,其特征在于,
检测自动再生时的柴油机微粒消除器再生的废气温度,求出检测的废气温度和再生目标温度的偏差,并基于该偏差对后喷射量进行PID控制的情况下,在从行驶自动再生转移至停车的怠速自动再生时,将PID控制中的积分控制项复位为零,从而对后喷射量进行控制。
2.如权利要求1所述的废气净化***,其中,
从上述停车后的怠速自动再生开始起,在规定时间以内转移至行驶自动再生时,通过上述怠速自动再生将积分控制项复位为零,并通过复位为零后的PID控制直接对后喷射量进行控制。
3.如权利要求1所述的废气净化***,其中,
从上述停车后的怠速自动再生开始起,超过规定时间而转移至行驶自动再生时,再次将PID控制的积分控制项复位为零。
4.如权利要求2或3所述的废气净化***,其中,
上述规定时间为3分钟。
5.如权利要求1所述的废气净化***,其中,
从行驶自动再生将车减速而停车时,在减速时直接通过PID控制来继续后喷射,在停车后将PID控制的积分控制项复位为零。
6.如权利要求1~3中任意一项所述的废气净化***,其中,
在开始怠速自动再生时将排气制动阀关闭,在转移至行驶自动再生时将排气制动器打开。
7.如权利要求4所述的废气净化***,其中,
在开始怠速自动再生时将排气制动阀关闭,在转移至行驶自动再生时将排气制动器打开。
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