JPS6318123A - Catalytic converter - Google Patents

Abstract

PURPOSE:To suppress a laminar flow of exhaust gas in an upstream section of a catalytic converter having a plurality of monolith catalysts arranged in series, and effectively utilize the whole of the catalysts, by making a cell size of the upstream catalyst greater then that of the downstream catalyst. CONSTITUTION:A catalytic converter 21 comprises a substantially cylindrical converter case 22 and two monolith catalysts 23 and 24 arranged in series in the case 22 with cavities defined between axial ends of the catalysts. The converter case 22 includes a turbulence generating changer 28 defined at a central portion of a cylindrical shell 25 and upstream and downsteam catalyst chambers 29 and 30 defined on the upstream and downstream sides of the turbulence generating chamber 28. The catalysts 23 and 24 have a structure such that they are partitioned like a grid to define cells 31 and 32 which form axially extending exhaust gas passages. Each cell 31 of the upstream monolith catalyst 23 has a size greater than that of each cell 32 of the downstream monolith catalyst 24. Accordingly, a laminar flow of exhaust gas in the upstream section of the catalytic converter may be suppressed to maintain a turbulent condition of the exhaust gas, thereby improving the emission control.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a catalytic converter that is installed in an exhaust system of an engine used in a vehicle or the like to purify harmful components in exhaust gas.

[Prior Art and Problems to be Solved by the Invention] Conventionally, harmful components in engine exhaust gas have been reduced by passing them through a catalyst, such as IIc and Co, which are harmful components in exhaust gas.

There is a catalytic converter that chemically changes NOx, etc. into harmless ()-120, CO2, N2, etc. This catalyst is a monolithic catalyst in which gas passages are formed along the direction of exhaust gas flow by grid-like, honeycomb-like, etc. cells at the back of the catalyst used in the converter. It has the advantage of low pressure.

However, in the monolithic catalyst, the exhaust gas flow 1 changes from turbulent flow to laminar flow as it approaches the outlet due to the rectification effect of the gas passage. Therefore, in the monolithic catalyst, Co, HC, Diffusion and absorption reactions of NQx, etc. 1) do not proceed smoothly in the direction of flow of F gas,
The reaction is active on the upstream side where turbulence is maintained, but
Exhaust gas flowing through the center of the cell toward the downstream side passes through without touching the catalyst, resulting in poor purification efficiency.

To deal with this, for example, Japanese Utility Model Application Publication No. 55-83516 discloses that a plurality of catalysts are housed in series in a converter case with gaps on the end faces in the axial direction, and the gaps between the catalysts allow A technique has been disclosed for making a laminar exhaust gas flow turbulent again. The outline of this conventional example will be explained with reference to FIGS. 7 to 9. Figure 7 is a sectional view of the upper catalytic converter, Figure 8 is an explanatory diagram without showing the cell density of the monolith catalyst, and Figure 9 is an explanatory diagram showing the flow of exhaust gas.

In FIG. 7, the catalytic converter 1 includes a substantially cylindrical inverter case 2, an upstream monolithic catalyst 3 and a downstream monolithic catalyst 3 housed in series with a gap between the axial end faces in the converter case 2. It is composed of a catalyst 4. The converter case 2 includes a cylindrical body portion 5;
An inlet portion 6 is formed on the upstream side of the body portion 5 to have a smaller diameter than the body portion 5, and an outlet portion 7 is formed on the downstream side of the body portion 5 to have the same diameter as the inlet portion 6. have. The body portion 5
The diameter of the central part is slightly reduced for positioning the upstream monolithic catalyst 3 and the downstream monolithic catalyst 4, and a turbulent flow chamber 8 is formed inside this reduced diameter part. An upstream catalyst chamber 9 is formed on the upstream side of the fluidization chamber 8, and a downstream catalyst chamber 10 is formed on the downstream side. The upstream monolithic catalyst 3 is housed in the upstream catalyst chamber 9, and the downstream monolithic catalyst 4 is housed in the downstream catalyst chamber 10. As shown in FIGS. 8(a) and 8(b), the downstream monolithic catalyst 3 and the downstream monolithic catalyst 4 are provided with cells 11 and 12, respectively, which are partitioned into a lattice shape, for example, in the axial direction. An exhaust gas passage is formed.

Conventionally, the upstream monolithic catalyst 3 and the downstream monolithic catalyst 4 may have different lengths in the axial direction, but their cell densities are the same; for example, at present (400 cells/in2)
has become the mainstream.

Incidentally, in recent years, there has been a tendency to use catalysts with smaller cell sizes in order to increase the surface area of the catalyst.

However, as shown in FIGS. 6(a) and 6(b), the smaller the size of the catalyst cells 14, the greater the rectification performance. Therefore, when the cell size of the upstream monolithic catalyst 3 is reduced (the cell density is increased), as shown in FIG. 9, the exhaust gas 13 reaches the upstream monolithic catalyst III! 3, the flow is highly rectified and laminarized.

This laminarized exhaust gas 13 is made into a slightly turbulent flow in the turbulence chamber 8, but the degree of turbulence is small, and therefore, in the downstream monolithic catalyst 4, unreacted molecules reach catalytic active sites. There is a problem that adsorption becomes difficult to proceed and exhaust gas purification performance deteriorates.

[Purpose of the present invention] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a catalytic converter that can effectively utilize the entire catalyst to improve exhaust gas purification performance. .

[Means for Solving the Problems] The catalyst inverter according to the present invention is a monolithic catalyst in which gas passages are formed by a plurality of cells, and a gap is formed between the axial end faces along the flow direction of exhaust gas. In a case where a plurality of monolithic catalysts are arranged in series, the cell size of the upstream monolithic catalyst is larger than the cell size of the downstream monolithic catalyst.

[Effect: By increasing the cell j method of the upstream monolith catalyst, the laminar flow of the exhaust gas passing through the cells of the upstream monolith catalyst was suppressed, and the exhaust gas maintained a turbulent flow. It continues to flow into the monolithic catalyst on the downstream side. Further, the cell size of the monolithic catalyst on the downstream side is smaller than the cell size of the monolithic catalyst on the upstream side, and the surface area of the catalyst is larger. Therefore, the exhaust gas that has passed through the upstream monolith catalyst is also effectively purified by the downstream monolith catalyst.

[Example] Hereinafter, the present invention will be described in detail with reference to the drawings.

Figures 1 to 3 relate to the first embodiment of the present invention.
The figure is a sectional view of the catalytic converter, FIG. 2 is an explanatory diagram showing the cell density of the monolith catalyst, and FIG. 3 is an explanatory diagram showing the flow of exhaust gas.

The catalyst-J converter 21 according to this embodiment includes a substantially cylindrical converter case 22, and a plurality of, for example, two monolithic catalysts, housed in series with a gap between the axial end faces in the converter case 22. Now, the upstream monolith catalyst 23 and the downstream monolith are in contact! ! ! It consists of 24. The converter case 22 is cylindrical)
an inlet portion 26 formed on the upstream side of the body portion 25 to have a smaller diameter than the body portion 25 and communicating with an exhaust system of an engine (not shown); and an inlet portion 26 on the downstream side of the body portion 25, for example. The body part 25 has an outlet part 27 formed to have the same diameter as the part 26. The central part of the body part 25 connects the downstream monolithic catalyst 23 and the downstream monolithic catalyst 24 to the axial end surface 23a.
, 24a are made slightly smaller in diameter or have a convex portion formed on the inner circumferential surface of the central portion in order to position them with a gap in the center. A turbulence chamber 28 is formed in the center of the body 25, and an upstream catalyst chamber 29 is provided upstream of the turbulence chamber 28.
However, a downstream catalyst chamber 30 is also formed on the downstream side. The upstream monolith catalyst 23 is housed in the upstream catalyst chamber 29, and the downstream catalyst chamber 30
The downstream monolithic catalyst 24 is housed in the downstream side monolithic catalyst 24 . The upstream monolith catalyst 23 and the downstream monolith catalyst 24 are made of platinum (Pt), palladium (Pd), rhodium<nh
>, or a combination thereof is used to act as an oxidation catalyst or three-way catalyst. Also, this upstream monolith catalyst 23 and downstream monolith contact! l! In It24, as shown in FIG. 2(a) and (b), respectively,
For example, cells 31 and 32 partitioned into a grid pattern
An exhaust gas passage is formed in the axial direction.

In this embodiment, the cells 31 of the upstream monolith catalyst 23
The zero dimension is larger than the size of the cells 32 of the downstream monolith contact ff24 (the density of the cells 31 is smaller than the density of the cells 32).

For example, while the cell density of the downstream monolithic catalyst 24 is 400 cells/in2, the cell density of the downstream monolithic catalyst 23 is 200 cells/in2, or the cell density of the downstream monolithic catalyst is 600 cells/in2. On the other hand, the cell density of the upstream monolith catalyst is 3001? le/1
n2.

Next, the operation of the embodiment with the above configuration will be explained with reference to FIG. 3.

Exhaust gas 33 that has flowed into the body section 25 from the inlet section 26 of the catalytic converter 21 first flows through the cells 31 of the upstream monolith catalyst 23 in a turbulent state and is purified. At this time, since the cells 31 of the upstream monolithic catalyst 23 are large in size, the exhaust gas 33 is prevented from becoming a laminar flow, and flows out from the upstream monolithic catalyst 23 while maintaining a turbulent flow. Next, the degree of turbulence of the exhaust gas 33 is increased by the turbulence chamber 28, and the exhaust gas 33 flows into the downstream monolith catalyst 24.

Since this exhaust gas 33 is maintained in a turbulent state,
In addition to efficiently contacting the catalyst of the downstream monolithic catalyst 24, the dimensions of the cells 32 of the downstream monolithic catalyst 24 are smaller than the dimensions of the cells 31 of the upstream monolithic catalyst 23, and the surface area of the catalyst is increased. Therefore, even if J3 is present in this downstream monolithic catalyst 24, it is efficiently purified.

In this way, according to this embodiment, the upstream monolith contact 9X
23 and the downstream monolith catalyst 24 can be used effectively,
The purification performance of the exhaust gas 33 is improved.

4 and 5 relate to a second practical example of the present invention; FIG. 4 is a sectional view of a catalytic converter, and FIG. 5 is an explanatory diagram showing the hill density of a monolithic catalyst.

The catalytic converter 41 according to the present embodiment has a first monolith catalyst 43, a second monolith catalyst 44, and a third monolith catalyst arranged in series in a converter case 42 with a gap between the end faces in the axial direction. Three monolithic catalysts, ie, monolithic catalyst 45, are housed therein.

The cell dimensions of the three monolithic catalysts are the smallest at the third monolithic catalyst 45 on the most downstream side, and increase as they go upstream from this third monolithic catalyst 45 (the cell density is on the downstream side J, The upstream side is smaller). For example, if the density of the cells 4G of the first monolith catalyst 43 is 200 cells/in2, and the density of the cells 4G of the first monolith catalyst 43 is 200 cells/in2,
The sound intensity of the fourth cell 47 is 400 cells/in2, and the density of the cell 48 of the third monolith catalyst 45 is 600 cells/in2.

According to this embodiment, since the cell size of the upstream monolithic catalyst is larger than that of the downstream monolithic catalyst, the exhaust gas flows through the three monolithic catalysts while suppressing laminar flow and maintaining turbulence. 43, 44, and 45 is passed through and agarized, the purification performance is improved.

Other functions and effects are similar to those of the first embodiment.

Note that the present invention is not limited to the above embodiments, and for example, the hills of the monolithic catalyst are not limited to a lattice shape, but may be honeycomb-shaped, spiral-shaped, or the like.

[Effects of the Invention] As explained above, according to the present invention, by making the hill size of the monolithic catalyst on the second-stream side larger than the hill size on the downstream side, laminarization of exhaust gas on the upstream side is suppressed. The effect is that the entire catalyst can be used effectively and the exhaust gas purification performance can be improved. There is.

[Brief explanation of drawings]

Figures 1 to 3 relate to the first embodiment of the present invention.
Figure 2 is a cross-sectional view of the catalytic converter, Figure 2 is a diagram showing the cell density of the monolithic catalyst, Figure 3 is an explanatory diagram showing the flow of exhaust gas, Figures 4 and 5 are the second diagram of the present invention. Regarding the examples, Fig. 4 is a cross-sectional view of the catalytic converter, Fig. 5 is an explanatory drawing showing the cell density of the monolith catalyst, Fig. 6 is an explanatory drawing showing the relationship between cell size and rectification performance, and Fig. 7 is an explanatory drawing showing the relationship between cell size and rectification performance. 9 to 9 relate to the conventional example, FIG. 7 is a sectional view of the catalytic converter, and FIG. 8 is a sectional view of the catalytic converter.
The figure is an explanatory diagram showing the cell density of the monolithic catalyst, and FIG. 9 is an explanatory diagram showing the flow of exhaust gas. 21... Catalytic converter 22... Converter case 23... Upstream monolith catalyst 24... Downstream monolith catalyst 26... Inlet section 27... Outlet section 28...
Turbulence chamber 31.32...Cell 33--Exhaust gas

Claims (1)

[Claims] In a catalytic converter in which a plurality of monolithic catalysts each having a gas passage formed by a plurality of cells are arranged in series along the flow direction of exhaust gas with a gap between the axial end faces, the upstream monolithic catalyst A catalytic converter characterized in that the cell size of the catalyst is larger than that of a downstream monolith catalyst.