1. Field of the Invention
The present invention relates to an exhaust gas purification filter that purifies exhaust gas by trapping particulate matter contained in exhaust gas discharged from internal combustion engines.
2. Description of the Related Art
There is an exhaust gas purification filter according to the prior art that purifies exhaust gas by trapping particulate matter contained in exhaust gas discharged from internal combustion engines.
Said exhaust gas purification filter has a honeycomb structure consisting of partitions having a large number of pores and cells separated by said partitions.
During purification of exhaust gas using said exhaust gas purification filter, exhaust gas is led into the above cells, passes through the above partitions and moves to the adjacent cell. At this time, particulate matter contained in the above exhaust gas is purified by being trapped in the above partitions. In addition, by loading a catalyst, for example, onto the above partitions, the trapped particulate matter can be decomposed and removed by a catalytic reaction.
It is important for the performance of the above exhaust gas purification filter that the exhaust gas purification efficiency be high, and that pressure loss of the exhaust gas that passes through the filter be small.
Therefore, as is disclosed in Japanese Patent Publication No. 2726616, an exhaust gas purification filter is proposed that improves performance by specifying porosity, pore diameter and so forth within prescribed ranges.
However, with the demand for exhaust gas purification filters offering even higher performance in recent years, it is difficult to adequately improve exhaust gas purification efficiency and reduce exhaust gas pressure loss even with the above exhaust gas purification filter of the prior art.
Namely, as shown in FIG. 6, each pore 93 in partitions 91 of the above exhaust gas purification filter has a non-uniform surface opening diameter and pore diameter. Consequently, a phenomenon occurs in which particulate matter is deposited on surface 911 of the above partitions 91 and clogs openings 931 of pores 93 or particulate matter is not trapped by the above partitions 91 and ends up being discharged. As a result, it is difficult to achieve adequate improvement of purification efficiency or reduction of pressure loss.
In consideration of the above problems of the prior art, the object of the present invention is to provide an exhaust gas purification filter having high purification efficiency and low pressure loss.
A first aspect of the invention is an exhaust gas purification filter that purifies exhaust gas by trapping particulate matter contained in exhaust gas discharged from an internal combustion engine; wherein,
said exhaust gas purification filter has a honeycomb structure composed of partitions having a large number of pores, and cells separated by said partitions, and
the surface opening area ratio of said partitions attributable to pores having a surface opening diameter of 10 xcexcm or less is 20% or less of the total surface opening area ratio.
The surface opening area ratio of the above partitions attributable to pores having a surface opening diameter of 10 xcexcm or less is 20% or less of the total surface opening area ratio. Namely, there are few pores for which the surface opening diameter is excessively small that are comparatively susceptible to clogging of the openings by particulate matter. Consequently, the clogging of the openings of the pores by particulate matter and the deposition of particulate matter on the above partitions can be prevented.
As a result, exhaust gas can be adequately led into the above pores. For this reason, exhaust gas purification efficiency can be made to be adequately high. In addition, the pressure loss of exhaust gas led into the above exhaust gas purification filter can be held to a low level.
As has been described above, according to a first aspect of the invention, an exhaust gas purification filter can be provided that has high purification efficiency and low pressure loss.
A second aspect of the invention is an exhaust gas purification filter that purifies exhaust gas by trapping particulate matter contained in exhaust gas discharged from an internal combustion engine; wherein,
said exhaust gas purification filter has a honeycomb structure composed of partitions having a large number of pores and cells separated by said partitions,
the porosity of said partitions attributable to pores having a pore diameter of less than 10 xcexcm is 10% or less, and
the porosity attributable to pores having a pore diameter in excess of 70 xcexcm is 10% or less.
The porosity of the above partitions attributable to pores having a pore diameter of 10 xcexcm or less is 10% or less. Namely, there are few pores for which pore diameter is excessively small, which is a cause of increased pressure loss of exhaust gas led into the above exhaust gas purification filter. Consequently, the pressure loss of the exhaust gas can be held to a low level.
In addition, since there are few pores for which pore diameter is excessively small, which are comparatively susceptible to clogging by particulate matter, deposition of particulate matter on the partitions can be prevented. Consequently, exhaust gas can be adequately led into the pores and purification efficiency can be increased.
In addition, the porosity attributable to pores having a pore diameter in excess of 70 xcexcm is 10% or less. Namely, there are few pores for which pore diameter is excessively large that make it comparatively difficult to trap particulate matter. Consequently, the above partitions are able to adequately trap particulate matter. For this reason, the above exhaust gas purification filter is able to adequately increase purification efficiency.
As has been described above, according to a second aspect of the invention, an exhaust gas purification filter can be provided having high purification efficiency and low pressure loss.