CN105593482B - 排气净化系统 - Google Patents

排气净化系统 Download PDF

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CN105593482B
CN105593482B CN201480052973.8A CN201480052973A CN105593482B CN 105593482 B CN105593482 B CN 105593482B CN 201480052973 A CN201480052973 A CN 201480052973A CN 105593482 B CN105593482 B CN 105593482B
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electrostatic capacitance
adsorbance
urea water
reduction catalyst
scr
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CN105593482A (zh
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内山正
藤江英和
村泽直人
塙哲史
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Isuzu Motors Ltd
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Abstract

对于排气净化系统，高精度地检测内部的NH3吸附量。具备：SCR(32)，设置于发动机(10)的排气系统，将从尿素水生成的氨作为还原剂，对排气中含有的NOx进行还原净化；尿素水喷射装置(31)，向SCR(32)喷射尿素水；入口侧电极(37)，检测SCR(32)内的至少入口侧附近至排气流动方向的中间部附近的静电电容；出口侧电极(38)，检测SCR(32)内的至少排气流动方向的中间部附近至出口侧附近的静电电容；NH3吸附量运算部(52)，基于从入口侧电极(37)以及出口侧电极(38)输入的静电电容，运算SCR(32)内的氨吸附量。

Description

排气净化系统
技术领域
本发明涉及排气净化系统，特别涉及具备将排气中的氮化合物(NOx)还原净化的NOx催化剂的排气净化系统。
背景技术
作为设置在柴油发动机等的排气系统中的NOx催化剂，已知将由尿素水加水分解而生成的氨(NH3)作为还原剂、将排气中的NOx选择性地还原净化的选择性还原催化剂(Selective Catalytic Reduction：SCR)。
若向SCR的尿素水喷射量过多而NH3供给量超过了SCR对NH3的吸附能力，则多余的NH3溢出而被放出到大气中，这是不希望出现的。因此，已知如下技术：基于在SCR出口设置的NH3传感器的检测值，推测SCR内的NH3吸附量，并且与推测出的NH3吸附量相应地适当修正向SCR的尿素水喷射量(例如参照专利文献1)。
现有技术文献
专利文献
专利文献1：特开2003-293737号公报
发明内容
发明所要解决的技术课题
一般而言，SCR内部的NH3吸附量处于入口侧比出口侧多的不均匀的分布。NH3传感器无法直接设置于SCR内部，因此存在无法准确地掌握SCR内部的实际的NH3吸附量的课题。因此，在根据NH3传感器的传感器值来推测NH3吸附量的技术中，可能无法将尿素水喷射量修正成与实际的NH3吸附量对应的最佳的喷射量。
本发明的系统的目的在于，高精度地检测SCR内部的NH3吸附量。
解决课题所采用的技术手段
本发明的系统具备：至少一个以上选择性还原催化剂，设置于内燃机的排气系统，将从尿素水生成的氨作为还原剂，对排气中含有的氮化合物进行还原净化；尿素水喷射机构，向所述选择性还原催化剂喷射尿素水；第1静电电容检测机构，检测所述选择性还原催化剂内的至少入口侧附近至排气流动方向的中间部附近的静电电容；第2静电电容检测机构，检测所述选择性还原催化剂内的至少排气流动方向的中间部附近至出口侧附近的静电电容；以及还原剂吸附量运算机构，基于从所述第1以及第2静电电容检测机构输入的静电电容，运算所述选择性还原催化剂内的还原剂吸附量。
发明的效果：
根据本发明的系统，能够高精度地检测SCR内部的NH3吸附量。
附图说明
图1是表示本发明的一个实施方式的排气净化系统的示意性的整体构成图。
图2是表示本实施方式的电极的配置样式的一例的图。
图3是表示本实施方式的ECU的功能框图。
图4是表示本实施方式的静电电容·温度特性映射图的一例的图。
图5是表示本实施方式的静电电容·NH3吸附量映射图的一例的图。
图6是表示本实施方式的NH3可吸附量映射图的一例的图。
图7是表示本实施方式的控制内容的流程图。
图8是表示其他实施方式的排气净化系统的示意性整体构成图。
具体实施方式
以下，基于附图说明本发明的一个实施方式的排气净化系统。对相同的部件赋予相同的符号，其名称及功能也相同。因此，不重复详细说明。
如图1所示，柴油发动机(以下仅称作发动机)10中设置有吸气歧管10a和排气歧管10b。吸气歧管10a上连接着用于导入新气的吸气通路11，排气歧管10b上连接着用于将排气向大气放出的排气通路12。
吸气通路11中从吸气上游侧起依次设置有空气滤清器13、增压机15的压缩机15a、中冷器17等。在排气通路12中，从排气上游侧起依次设置有增压机15的涡轮15b、前段后处理装置20、后段后处理装置30等。另外，在图1中，符号18表示发动机转速传感器，符号19表示油门开度传感器。
前段后处理装置20是在催化剂壳体20a内从排气上游侧起依次配置氧化催化剂(Diesel Oxidation Catalyst：以下记作DOC)21和柴油颗粒过滤器(Diesel ParticulateFilter，以下记作DPF)22而构成的。此外，在DOC21的排气上游侧设置有排气管内喷射装置23。
排气管内喷射装置23按照从电子控制单元(以下记作ECU)50输入的指示信号，向比DPC21靠上游侧的排气通路12内喷射未燃燃料(主要为HC)。另外，在使用基于发动机10的多级喷射的后喷射的情况下，也可以省略该排气管内喷射装置23。
DOC21例如是在堇青石蜂窝(cordierite Honeycomb)构造体等的陶瓷制担载体表面上担载催化剂成分而形成的。当通过排气管内喷射装置23或者后喷射被供给了未燃燃料(HC)时，DOC21将该未燃燃料氧化而使排气温度上升。
DPF22例如是沿着排气流动方向配置由多孔质性的分隔壁划分出的多个单元格、并使这些单元格的上游侧和下游侧交替地封口而形成的。DPF22将排气中的PM捕获到分隔壁的细孔或表面，并且，当推测的PM堆积量达到规定量时，执行将其燃烧除去的所谓的强制再生。强制再生是通过排气管内喷射装置23或者后喷射向DOC21供给未燃燃料(HC)来使向DPF22流入的排气温度升温至PM燃烧温度(例如约500～600℃)而进行的。
后段后处理装置30从排气上游侧起依次具备尿素水喷射装置31和收容于壳体30a内的SCR32而构成。
尿素水喷射装置31是本发明的尿素水喷射机构的一例，按照从ECU50输入的指示信号，向比SCR32靠上游侧的排气通路12内喷射未图示的尿素水罐内的尿素水。所喷射的尿素水由于排气热而被加水分解，生成为NH3，作为还原剂被供给至下游侧的SCR32。
SCR32例如是在蜂窝构造体等的陶瓷制担载体表面上担载沸石等而形成的，是沿着排气流动方向配置由多孔质性的分隔壁划分出的多个单元格而构成的。SCR32吸附作为还原剂而被供给的NH3，并且利用所吸附的NH3从经过的排气中将NOx选择性地还原净化。此外，本实施方式的SCR32中分别设置有多个入口侧电极37及出口侧电极38，该多个入口侧电极37及出口侧电极38隔着至少一个以上分隔壁而对置配置，从而形成电容器。
入口侧电极37在SCR32的单元格内从入口(上游)侧插入到排气流动方向的大致中央部附近。出口侧电极38在SCR32的单元格内从出口(下游)侧插入到排气流动方向的大致中央部附近。入口侧电极37以及出口侧电极38的外周面被耐腐蚀性的绝缘层(未图示)覆盖。这些入口侧电极37以及出口侧电极38均经由未图示的静电电容检测电路分别电连接到ECU50。这些入口侧电极37、出口侧电极38以及静电电容检测电路(未图示)是本发明的静电电容检测机构的一例。
另外，作为入口侧电极37以及出口侧电极38的排列样式，例如优选为如图2(A)所示那样在SCR32的径向上并列设置两列的样式、或如图2(B)所示那样使径向的两列相互交叉的样式等。由此，能够有效地检测SCR32内部的整体的静电电容。
ECU50用于进行发动机10或尿素水喷射装置31等的各种控制，具备公知的CPU、ROM、RAM、输入端口及输出端口等而构成。
此外，ECU50如图3所示，具备SCR内部温度运算部51、NH3吸附量运算部52、尿素水喷射控制部53、喷射量修正部54，来作为一部分功能要素。说明了这些各功能要素被包含于作为一体的硬件的ECU50中情况，但是也可以将这些各功能中的任意一部分设置于另外的硬件。
SCR内部温度运算部51是本发明的内部温度运算机构的一例，基于入口侧电极37间的静电电容、以及出口侧电极38间的静电电容，运算SCR32的内部温度。一般而言，电极37间、电极38间的静电电容C由以下的数式1表示。其中，ε为电极37间、电极38间的介质的介电常数，S为电极37、38的面积，d为电极37间、电极38间的距离。
[数1]
数式1中，电极37、38的面积S以及距离d是恒定的，介电常数ε受到排气温度的影响而变化时，静电电容C也随之变化。即，若检测出电极37间、电极38间的静电电容C，则能够运算SCR32的内部温度。
ECU50中存储有预先通过试验等求出的、表示静电电容C与SCR内部温度T之间的关系的静电电容·温度特性映射图(例如参照图4)。SCR内部温度运算部51从静电电容·温度特性映射图中读取与入口侧电极37间的静电电容C对应的值，由此来运算SCR32的入口侧内部温度TSCR_IN。进而，从静电电容·温度特性映射图中读取与出口侧电极38间的静电电容C对应的值，由此来运算SCR32的出口侧内部温度TSCR_OUT。另外，这些入口侧内部温度TSCR_IN以及出口侧内部温度TSCR_OUT的运算除了基于映射图，也可以根据预先通过试验等制作出的近似式等来求出。
NH3吸附量运算部52是本发明的还原剂吸附量运算机构的一例，基于入口侧电极37间的静电电容以及出口侧电极38间的静电电容，运算吸附于SCR32的NH3实际吸附量。NH3的介电常数ε较高，所以在SCR32内NH3的吸附进展过程中，电极37间、电极38间的静电电容C也会增加(参照数式1)。即，如果检测出电极37间、电极38间的静电电容C，则能够运算SCR32的NH3实际吸附量。
ECU50中存储着预先通过试验等求出的、表示静电电容C与NH3实际吸附量STNH3之间的关系的静电电容·NH3吸附量映射图(例如参照图5)。NH3吸附量运算部52从静电电容·NH3吸附量映射图中读取与入口侧电极37间的静电电容C对应的值，由此来运算SCR32的入口侧NH3实际吸附量STNH3_IN。进而，从静电电容·NH3吸附量映射图中读取与出口侧电极38间的静电电容C对应的值，由此来运算SCR32的出口侧NH3实际吸附量STNH3_OUT。另外，这些入口侧NH3实际吸附量STNH3_IN以及出口侧NH3实际吸附量STNH3_OUT的运算除了基于映射图，也可以根据预先通过试验等制作出的近似式等来求出。
尿素水喷射控制部53是本发明的喷射控制机构的一例，基于发动机10的运转状态等来控制尿素水喷射装置31的尿素水喷射量。更详细地讲，尿素水喷射控制部53根据发动机转速Ne以及油门开度Q来运算发动机10的NOx排出量，并且与该NOx排出量相应地设定所需的尿素水的基本喷射量INJU_std。该基本喷射量INJU_std由后述的喷射量修正部54根据需要来修正。
喷射量修正部54是本发明的喷射量修正机构的一例，对由尿素水喷射控制部53设定的基本喷射量INJU_std，基于从SCR内部温度运算部51输入的入口侧内部温度TSCR_IN、出口侧内部温度TSCR_OUT及从NH3吸附量运算部52输入的入口侧NH3实际吸附量STNH3_IN、出口侧NH3实际吸附量STNH3_OUT进行修正。
更详细地讲，ECU50中存储着预先通过试验等制作出的、表示SCR32的内部温度TSCR与NH3可吸附量STNH3_MAX之间的关系的NH3可吸附量映射图(例如参照图6)。
喷射量修正部54从NH3可吸附量映射图中读取与当前的入口侧内部温度TSCR_IN对应的入口侧可吸附量STNH3_MAX_IN相对于当前的入口侧NH3实际吸附量STNH3_IN而言的入口侧吸附量偏差ΔSTNH3_IN(＝STNH3_MAX_IN－STNH3_IN)。进而，从NH3可吸附量映射图中读取与当前的出口侧内部温度TSCR_OUT对应的出口侧可吸附量STNH3_MAX_OUT相对于当前的出口侧NH3实际吸附量STNH3_OUT而言的出口侧吸附量偏差ΔSTNH3_OUT(＝STNH3_MAX_OUT－STNH3_OUT)。然后，基于与这些入口侧吸附量偏差ΔSTNH3_IN和出口侧吸附量偏差ΔSTNH3_OUT的总和ΔSTNH3(＝ΔSTNH3_IN+ΔSTNH3_OUT)相当的喷射修正量ΔINJ，对基本喷射量INJU_std进行增减修正(INJU_exh＝INJU_std+/－ΔINJ)。修正后的尿素水喷射通过增减对尿素水喷射装置31的喷射器(未图示)施加的各喷射的通电脉冲宽度来执行，或者通过增减喷射次数来执行。
接下来，基于图7对本实施方式的排气净化系统的控制流程进行说明。另外，本控制与点火键的接通操作同时开始。
在步骤(以下将步骤仅记作S)100中，与根据发动机转速Ne以及油门开度Q运算出的发动机10的NOx排出量相应地，设定尿素水的基本喷射量INJU_std。
在S110中，基于入口侧电极37间的静电电容C，运算SCR32的入口侧内部温度TSCR_IN，并且，基于出口侧电极38间的静电电容C，运算SCR32的出口侧内部温度TSCR_OUT。
在S120中，基于入口侧电极37间的静电电容C，运算SCR32的入口侧NH3实际吸附量STNH3_IN，并且基于出口侧电极38间的静电电容C，运算SCR32的出口侧NH3实际吸附量STNH3_OUT。
在S130中，根据NH3可吸附量映射图(图6)，运算与S110中运算出的入口侧内部温度TSCR_IN对应的入口侧可吸附量STNH3_MAX_IN以及与S110中运算出的出口侧内部温度TSCR_OUT对应的出口侧可吸附量STNH3_MAX_OUT。
在S140中，运算S130中运算出的入口侧可吸附量STNH3_MAX_IN与S120中运算出的入口侧NH3实际吸附量STNH3_IN之间的入口侧吸附量偏差ΔSTNH3_IN(＝STNH3_MAX_IN－STNH3_IN)，并且，运算S130中运算出的出口侧可吸附量STNH3_MAX_OUT与S120中运算出的出口侧NH3实际吸附量STNH3_OUT之间的出口侧吸附量偏差ΔSTNH3_OUT(＝STNH3_MAX_OUT－STNH3_OUT)。
在S150中，判定S140中运算出的入口侧吸附量偏差ΔSTNH3_IN与出口侧吸附量偏差ΔSTNH3_OUT的总和ΔSTNH3(＝ΔSTNH3_IN+ΔSTNH3_OUT)是否多于规定的阈值。在总和ΔSTNH3多于规定的阈值的情况下(Yes)，前进至S160，基于与该总和ΔSTNH3相当的喷射修正量ΔINJ，对基本喷射量INJU_std进行增减修正(INJU_exh＝INJU_std+/－ΔINJ)。进而，在S170中，基于修正后的喷射量INJU_exh，执行尿素水喷射装置31的尿素水喷射。
另一方面，在S150中判定为总和ΔSTNH3小于规定的阈值的情况下(否)，前进至S180，不进行修正而基于S100中设定的基本喷射量INJU_std来执行尿素水喷射装置31的尿素水喷射。然后，反复执行上述的S100～180的各控制步骤，直至点火键的关闭操作为止。
接下来，对本实施方式的排气净化系统的作用效果进行说明。
以往，作为抑制SCR的NH3溢出的技术，已知有如下手法：基于在SCR出口设置的NH3传感器的检测值，推测SCR内的NH3吸附量，并且，与推测出的NH3吸附量相应地对尿素水喷射量进行修正。然而，在根据NH3传感器的传感器值来进行推测的手法中，无法准确地掌握SCR内部的实际的NH3吸附量，可能无法最佳地控制尿素水喷射量。
与此相对，在本实施方式的排气净化系统中，基于从SCR32的入口侧插入至中间部的入口侧电极37间的静电电容、以及从SCR32的出口侧插入至中间部的出口侧电极38间的静电电容，来直接地运算SCR32内部的NH3吸附量，并且与准确的NH3实际吸附量相对于NH3可吸附量的差相应地适当修正尿素水喷射量。
因此，根据本实施方式的排气净化系统，能够在从SCR32内部的入口侧至出口侧的整个区域来高精度检测NH3吸附量。此外，能够与SCR32的NH3实际吸附量相应地准确控制尿素水喷射量，能够可靠地防止SCR32的NH3溢出，并且还能够有效地提高NOx的还原净化率。而且，无需在SCR32的下游侧配置将多余的NH3氧化除去的DOC等，还能够有效地减少装置整体的成本及重量·尺寸等。
另外，本发明不限于上述的实施方式，能够在不脱离本发明的主旨的范围内适当地变形来实施。
例如，也可以如图8所示那样，与SCR32的容量等相应地分割配设多个SCR32(图示例中为2个)。该情况下，在各SCR32a、32b中分别设置入口侧电极37以及出口侧电极38即可。此外，电极37、38的个数为至少一对以上即可，不限于图示例。此外，发动机10不限于柴油发动机，也广泛地应用于汽油发动机等其他内燃机。
符号的说明：
10 发动机
12 排气通路
18 发动机转速传感器
19 油门开度传感器
30 后段后处理装置
31 尿素水喷射装置
32 SCR
37 入口侧电极
38 出口侧电极
50 ECU
51 SCR内部温度运算部
52 NH3吸附量运算部
53 尿素水喷射控制部
54 喷射量修正部

Claims (2)

1.一种排气净化系统，其特征在于，具备：
至少一个以上选择性还原催化剂，设置于内燃机的排气系统，将从尿素水生成的氨作为还原剂，对排气中含有的氮化合物进行还原净化；
尿素水喷射机构，向所述选择性还原催化剂喷射尿素水；
第1静电电容检测机构，检测所述选择性还原催化剂内的至少入口侧附近至排气流动方向的中间部附近的静电电容；
第2静电电容检测机构，检测所述选择性还原催化剂内的至少排气流动方向的中间部附近至出口侧附近的静电电容；以及
还原剂吸附量运算机构，基于从所述第1静电电容检测机构和所述第2静电电容检测机构输入的静电电容，运算所述选择性还原催化剂内的还原剂吸附量，
所述第1静电电容检测机构由在所述选择性还原催化剂的单元格内从入口侧插入至排气流动方向的中间部附近而形成电容器的至少一对以上电极构成，
所述第2静电电容检测机构由在所述选择性还原催化剂的单元格内从出口侧插入至排气流动方向的中间部附近而形成电容器的至少一对以上电极构成，
所述第1静电电容检测机构的至少一对以上电极和所述第2静电电容检测机构的至少一对以上电极，(i)以在所述选择性还原催化剂的径向上并列设置两列的样式配置，或者(ii)以在所述选择性还原催化剂的径向上相互交叉的样式配置。
2.如权利要求1记载的排气净化系统，还具备：
喷射控制机构，至少基于与所述内燃机的运转状态相应地设定的规定的基准喷射量，控制所述尿素水喷射机构的尿素水喷射；以及
喷射量修正机构，基于从所述还原剂吸附量运算机构输入的还原剂吸附量，对所述基准喷射量进行修正。
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US20160245141A1 (en) 2016-08-25
WO2015053324A1 (ja) 2015-04-16
CN105593482A (zh) 2016-05-18
JP6206065B2 (ja) 2017-10-04
EP3056701A4 (en) 2017-06-07
EP3056701B1 (en) 2018-09-05

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