CN103635664A - 内燃机的排气净化装置 - Google Patents

内燃机的排气净化装置 Download PDF

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CN103635664A
CN103635664A CN201180070529.5A CN201180070529A CN103635664A CN 103635664 A CN103635664 A CN 103635664A CN 201180070529 A CN201180070529 A CN 201180070529A CN 103635664 A CN103635664 A CN 103635664A
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sensor
nox catalyzer
filter
exhaust
urea
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CN103635664B (zh
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中野隆德
片山晴之
广田信也
利冈俊祐
福田光一朗
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Toyota Motor Corp
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    • 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
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    • 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
    • F01N13/0093—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 the purifying devices are of the same type
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    • 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
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    • 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
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Abstract

本发明的目的在于，在内燃机的排气通路中的比颗粒过滤器（过滤器）更下游侧设置尿素添加部及选择还原型NOx催化剂（NOx催化剂）的结构中还在比过滤器更下游侧设置PM传感器的情况下，抑制PM传感器的劣化及PM量的检测精度的降低。本发明在内燃机（1）的排气通路（2）中，在比过滤器（3）更下游侧沿着排气的流向从上游侧依次设置第一NOx催化剂（4）和第二NOx催化剂（5）。并且在过滤器（3）和第一NOx催化剂（4）之间设置尿素添加部（6），在第一NOx催化剂（4）和第二NOx催化剂（5）之间设置PM传感器（7）。

Description

内燃机的排气净化装置
技术领域
本发明涉及内燃机的排气净化装置。
背景技术
已知在内燃机的排气通路中设置颗粒过滤器（以下有时简称过滤器）、选择还原型NOx催化剂（以下有时简称NOx催化剂）等作为排气净化装置的技术。过滤器捕集由于内燃机中的燃料的燃烧而生成的排气中的颗粒状物质（Particulate Matter：以下有时称作PM）。NOx催化剂以氨为还原剂还原排气中的NOx。
专利文献1中公开了在内燃机的排气通路中设置过滤器，而且在比过滤器更靠下游侧的排气通路中设置PM传感器的技术。另外，专利文献1中记载了在过滤器和PM传感器之间的排气通路中设置NOx催化剂。
专利文献2中公开了下述技术：在排气路径中，在比氧化催化剂更靠下游侧的路径中设置第一NOx催化剂（第一SCR催化剂），在比第一NOx催化剂更靠下游侧的路径中设置能够比该第一NOx催化剂吸附更多的氨的第二NOx催化剂（第二SCR催化剂），而且在比第二NOx催化剂更靠上游侧的路径中设置尿素水提供单元。
专利文献3中公开了在排气通路中的比第一催化转换器更靠下游侧的通路中设置比该第一催化转换器容量大的第二催化转换器、并且在第一催化转换器和第二催化转换器之间设置O2传感器的技术。
在先技术文献
专利文献
专利文献1：特开2010-229957号公报
专利文献2：特开2011-052612号公报
专利文献3：特开平08-296430号公报
发明内容
发明要解决的问题
在排气通路中设置NOx催化剂的情况下，需要向该NOx催化剂提供作为还原剂的氨。因此，设置向比NOx催化剂更靠上游侧的排气中添加尿素的尿素添加部。从尿素添加部添加的尿素水解而产生的氨被提供给NOx催化剂。
另外，在排气通路中设置过滤器的情况下，有时为了检测通过该过滤器的PM量，而在比该过滤器更靠下游侧的通路中设置PM传感器。PM传感器是用于检测排气中的PM量的传感器。
这里，在排气通路中的过滤器的下游侧设置尿素添加部及NOx催化剂的结构中还在过滤器的下游侧设置PM传感器的情况下，当在尿素添加部的下游侧配置PM传感器时，存在由于从尿素添加阀添加的尿素导致PM传感器浸水的可能性。在由于尿素导致PM传感器浸水时，有促进PM传感器的劣化的担忧。
另外，如果附着在PM传感器上的尿素被排气加热，则有可能生成缩二脲、氰尿酸等源自氨的化合物。当生成该源自氨的化合物时，PM传感器有可能将该源自氨的化合物感测为PM。当PM传感器将该源自氨由来化合物感测为PM时，存在由PM传感器本应检测的、由燃料成分形成的PM量的检测精度降低的担忧。
本发明是鉴于上述问题而做出的，其目的在于，在内燃机的排气通路中的比过滤器更靠下游侧的通路中设置尿素添加部和NOx催化剂的结构中、还在比过滤器更靠下游侧的通路中设置PM传感器的情况下，抑制PM传感器的劣化以及PM量的检测精度的降低。
用于解决问题的手段
本发明在内燃机的排气通路中，在比过滤器更下游侧沿着排气的流向从上游侧依次设置第一NOx催化剂和第二NOx催化剂。并且，在过滤器和第一NOx催化剂之间设置尿素添加部，在第一NOx催化剂和第二NOx催化剂之间设置PM传感器。
更详细地，本发明涉及的内燃机的排气净化装置，包括：
设置在内燃机的排气通路中的颗粒过滤器；
设置在比所述颗粒过滤器更靠下游侧的排气通路中的第一选择还原型NOx催化剂；
设置在比所述第一选择还原型NOx催化剂更靠下游侧的排气通路中的第二选择还原型NOx催化剂；
设置在所述颗粒过滤器和所述第一选择还原型NOx催化剂之间的排气通路中的、用于向排气中添加尿素的尿素添加部；以及
设置在所述第一选择还原型NOx催化剂和所述第二选择还原型NOx催化剂之间的排气通路中的、用于检测排气中的颗粒状物质量的PM传感器。
这里，PM传感器也可以输出与排气中的PM量（流量）对应的信号，另外，也可以输出与自身堆积的PM量对应的信号。
根据本发明，通过在尿素添加部和PM传感器之间配置第一NOx催化剂，PM传感器难以由于尿素而浸水。因此，能够抑制PM传感器的劣化。
另外，根据本发明，通过在比第二NOx催化剂更上游侧配置PM传感器，与在比第二NOx催化剂更下游侧配置该PM传感器的情况相比，PM在过滤器中被氧化时PM传感器容易升温。其结果是，PM传感器中堆积的源自氨的化合物容易被去除。因此，能够抑制PM传感器的PM量的检测精度的降低。
另外，与PM传感器被配置在比第二NOx催化剂更下游侧的情况相比，PM传感器容易通过排气而升温。因此，在低温起动时等之类的PM传感器的温度低于其活性温度时，能够较早活化该PM传感器。
另外，本发明中，也可以使第一NOx催化剂的热容量小于第二NOx催化剂的热容量。由此，PM传感器更容易升温。
发明效果
根据本发明，当在排气通路中的比过滤器更下游侧设置尿素添加部及NOx催化剂的结构中、还在比过滤器更下游侧设置PM传感器时，能够抑制PM传感器的劣化及PM量的检测精度的降低。
附图说明
图1是示出实施例涉及的内燃机的排气系统的概略结构的图；
图2是示出实施例涉及的PM传感器的概略结构的图；
图3是示出PM传感器中的PM堆积量、PM传感器的电极间的电阻及PM传感器的输出值的关系的曲线图。
具体实施方式
以下，基于附图对本发明的具体实施方式进行说明。本实施例中记载的结构部件的尺寸、材质、形状、其相对配置等只要没有特别说明，则不表明发明的技术范围仅限定于这些。
<实施例>
这里，对将本发明涉及的内燃机的排气净化装置应用于车辆驱动用的柴油发动机的场合进行说明。但是，本发明涉及的内燃机不限于柴油发动机，也可以是汽油发动机等。
[排气系统的概略结构]
图1是示出本实施例涉及的内燃机的排气系统的概略结构的图。内燃机1是车辆驱动用的柴油发动机。内燃机1上连接有排气通路2。另外，图1中的箭头表示排气的流动方向。
排气通路2中设置有过滤器3。过滤器3捕集由于内燃机1中的燃料的燃烧而生成的排气中的PM。此外，过滤器3也可以承载有氧化催化剂、吸储还原型NOx催化剂、或选择还原型NOx催化剂等催化剂。通过过滤器3捕集PM，PM渐渐堆积在该过滤器3上。当随着排气温度的上升等而过滤器3的温度上升至能够氧化PM的温度时，堆积在该过滤器3上的PM被氧化。另外，通过执行使过滤器3的温度强制上升的所谓过滤器再生处理，也能够将堆积在该过滤器3上的PM氧化来去除。
在比过滤器3更靠下游侧的排气通路2中设置有第一选择还原型NOx催化剂（第一NOx催化剂）4。在比第一NOx催化剂4更靠下游侧的排气通路2中设置有第二选择还原型NOx催化剂（第二NOx催化剂）5。第一NOx催化剂4的热容量与第二NOx催化剂5的热容量相比较小。
在过滤器3和第一NOx催化剂4之间的排气通路2中设置有尿素添加阀6。尿素添加阀6向排气中添加尿素水溶液。尿素添加阀6上连接有存储有尿素水溶液的尿素容器（未图示）。从尿素容器向尿素添加阀6提供尿素水溶液。另外，尿素添加阀6与用于控制内燃机1的ECU（未图示）电连接，并由该ECU控制。此外，在本实施例中，尿素添加阀6相当于本发明涉及的尿素添加部。
通过从尿素添加阀6向排气中添加尿素水溶液，向第一及第二NOx催化剂4、5提供尿素。被提供至第一或第二NOx催化剂4、5的尿素临时吸附在各NOx催化剂4、5上。并且，吸附的尿素水解而产生氨。该氨作为还原剂而还原排气中的NOx。
此外，在本实施例中，在第一NOx催化剂4和第二NOx催化剂5之间的排气通路2中，设置有检测排气中的PM量的PM传感器7。该PM传感器7是输出与堆积在自身上的PM量相对应的电信号的传感器。
这里，基于图2及3来对PM传感器7的详细情况进行说明。图2是示出PM传感器7的传感器元件的概略结构的图。图3是示出PM传感器7中的PM堆积量与PM传感器7的电极7a、7b间的电阻以及PM传感器7的输出值之间的关系的曲线图。在图3中，横轴表示PM传感器7中的PM堆积量，下部分的纵轴表示PM传感器7的电极7a、7b间的电阻，上部分的纵轴表示PM传感器7的输出值。
如图2所示，PM传感器7的传感器元件具有一对栉齿型电极7a、7b。PM传感器7上，附着有排气中的PM，并且该附着的PM慢慢堆积。随着PM传感器7上的PM堆积量增加，电极7a、7b间存在的PM的量也增加。
因此，如图3所示，PM传感器7中的PM堆积量越多，电极7a、7b间的电阻就越低。并且电极7a、7b间的电阻越低，PM传感器7的输出值就越增大。因此，该PM传感器7的输出值是与PM传感器7中的PM堆积量对应的值。
另外，PM传感器7设置在比过滤器3更下游侧。因此，PM传感器7中捕集未被过滤器3捕集而通过了该过滤器3的PM。因此，该PM传感器7中的PM堆积量为与通过了过滤器3的PM量的累积值相对应的量。
PM传感器7与ECU电连接，PM传感器7的输出信号被输入至该ECU。在ECU中，基于该PM传感器7的输出值来进行过滤器3的故障诊断。当发生了破损、溶损等过滤器3的故障时，比起过滤器3处于正常状态时通过该过滤器3的PM量增加。因此，当预定时间段中的PM传感器7的输出值的变化量超过了预定阈值时，ECU判定为发生了过滤器3的故障。
此外，如果电极7a、7b间存在的PM的量发生了变化，则流过该电极7a、7b间的电流等除电阻之外的电特性值也会变化。因此，PM传感器7也可以基于除电阻之外的电特性值来输出与自身上堆积的PM量对应的信号。另外，本发明涉及的PM传感器不限于输出与自身上堆积的PM量对应的信号的传感器，也可以是输出与排气中的PM量（流量）对应的信号的传感器。
[本实施例涉及的结构的效果]
在传感器PM传感器设置在排气通路中的比尿素添加阀更下游侧的情况下，存在由于从尿素添加阀添加的尿素水溶液而导致PM传感器浸水的担忧。但是，在本实施例中，第一NOx催化剂4被配置在尿素添加阀6和PM传感器7之间。通过这样的结构，PM传感器7难以被尿素水溶液浸水。因此，能够抑制PM传感器7的劣化。
另外，当附着在PM传感器7上的尿素被排气加热时，有可能生成源自氨的化合物（缩二脲、氰尿酸等）。当PM传感器7中生成这样的源自氨的化合物时，PM传感器7有可能将该源自氨的化合物感测为PM。即，PM传感器7中，除了由燃料成分所形成的PM之外还堆积源自氨的化合物，由此电极7a、7b间的电阻比仅堆积PM的情况相比变低，其结果，PM传感器7有可能输出比该PM传感器7中的PM堆积量更大的值。如此，当PM传感器7将源自氨的化合物感测为PM时，存在由PM传感器7本应检测的、由燃料成分形成的PM量的检测精度降低的担忧。
这里，即使在比第二NOx催化剂5更靠下游侧的排气通路2中设置PM传感器7的情况下，也能够抑制由从尿素添加阀6添加的尿素水溶液引起的该PM传感器7的浸水。但是，如本实施例那样，当在比第二NOx催化剂5更靠上游侧的排气通路2中配置PM传感器7时，与在比第二NOx催化剂5更靠下游侧的排气通路2中配置PM传感器7的情况相比，PM传感器7容易受到PM在过滤器3中被氧化时产生的热量。因此，PM传感器7容易升温。
如果PM传感器7升温，则堆积在该PM传感器7中的源自氨的化合物被氧化而被去除。即，当在比第二NOx催化剂5更靠上游侧的排气通路2中配置PM传感器7时，与在比第二NOx催化剂5更靠下游侧的排气通路2中配置PM传感器7的情况相比，容易去除附着在PM传感器7上的源自氨的化合物。
另外，在本实施例中，第一NOx催化剂4的热容量比第二NOx催化剂5的热容量小。由此，当在过滤器3中PM被氧化时，PM传感器7更容易升温。因此，更容易促进附着在PM传感器7上的源自氨的化合物的去除。
因此，根据本实施例涉及的结构，能够抑制PM传感器7的PM量的检测精度的降低。其结果，也能够抑制上述那样的过滤器3的故障诊断中产生误诊断。
另外，当在比第二NOx催化剂5更靠上游侧的排气通路2中配置PM传感器7时，与在比第二NOx催化剂5更靠下游侧的排气通路2中配置PM传感器7的情况相比，PM传感器7更容易被排气升温。另外，由于第一NOx催化剂4的热容量比第二NOx催化剂5的热容量小，因此与PM传感器7通过过滤器3中的PM的氧化热而升温的情况同样，更容易促进PM传感器7通过排气的升温。因此，根据本实施例涉及的结构，当如低温启动时等之类的PM传感器7的温度低于其活性温度时，能够较早活化该PM传感器7。
符号说明
1…内燃机
2…排气通路
3…颗粒过滤器
4…第一选择还原型NOx催化剂
5…第二选择还原型NOx催化剂
6…尿素添加阀
7…PM传感器

Claims (2)

1.一种内燃机的排气净化装置，包括：
设置在内燃机的排气通路中的颗粒过滤器；
设置在比所述颗粒过滤器更靠下游侧的排气通路中的第一选择还原型NOx催化剂；
设置在比所述第一选择还原型NOx催化剂更靠下游侧的排气通路中的第二选择还原型NOx催化剂；
设置在所述颗粒过滤器和所述第一选择还原型NOx催化剂之间的排气通路中的、用于向排气中添加尿素的尿素添加部；以及
设置在所述第一选择还原型NOx催化剂和所述第二选择还原型NOx催化剂之间的排气通路中的、用于检测排气中的颗粒状物质量的PM传感器。
2.根据权利要求1所述的内燃机的排气净化装置，其中，
所述第一选择还原型NOx催化剂的热容量小于所述第二选择还原型NOx催化剂的热容量。
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