JPH04250856A - Metallic carrier for exhaust gas purifying catalyst of automobile - Google Patents

Abstract

PURPOSE:To decrease the noises radiated from the above carrier which is superposed and joined with metallic flat foil and metallic corrugated foil and is inserted into a metallic outside cylinder and to decrease the uncomfortable noises of high frequencies by constituting the above-mentioned outside cylinder of double layers of metallic plates in contact with each other and specifying the thickness of the outside cylinder to a specific thickness or above. CONSTITUTION:The above-mentioned carrier 1 which is superposed and joined with the metallic flat foil 3 and the metallic corrugated foil 4 is inserted into the metallic outside cylinder 6. This outside cylinder 6 is constituted of the double layers of the metallic plates 7, 8 in contact with each other and the thickness of the outside cylinder 6 is specified to >=1.6mm in total. Namely, the outside cylinder 6 is formed as thick as >=1.6mm in total and, therefore, the transmission sounds are drastically attenuated at the time of passing the outside cylinder 6. In addition, the outside cylinder 6 is made into the plural layers, by which the natural frequencies of the outside cylinder are lowered and the frequencies of the resonance sounds are lowered. Consequently, the noises radiated from the metal carrier are decreased and the uncomfortable noises of the high frequencies are decreased as well.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a catalyst metal carrier for purifying automobile exhaust gas.

0002

BACKGROUND OF THE INVENTION Catalytic converters are widely used to purify exhaust gas from automobiles and the like. Automotive catalytic converters typically use a three-way catalyst that simultaneously oxidizes and reduces three components, CO, HC, and NOx in exhaust gas. Pt/Rh, Pd/Rh, etc. are used as catalysts, and metal carriers are beginning to be employed as substrates for γ-alumina supporting these catalysts. The metal carrier is formed by alternately stacking flat metal foils and corrugated metal foils to form a honeycomb, and the corrugated foils support the catalyst. As a foil material, 2
A heat-resistant metal material such as 0Cr-5Al stainless steel is used. Further, the thickness of the foil is about 50 μm. The flat foil and the corrugated foil are joined by brazing or the like. The honeycomb has a cylindrical or racetrack cross-section, C
It is inserted into an outer cylinder made of heat-resistant steel such as R steel or Ni-Cr steel. The catalytic converter is installed between the exhaust manifold and the muffler.

0003

[Problems to be Solved by the Invention] In the metal carrier, the flat foil and the corrugated foil are joined as described above, and the honeycomb thus formed is directly joined to the outer cylinder. On the other hand, the exhaust gas flowing through this still contains the engine's explosion sound and exhaust sound vibrations, so it vibrates the outer cylinder through the joint, and the metal carrier emits loud noise. In particular, the racetrack type metal carrier has a structure in which the parallel portions of the outer cylinder are likely to vibrate due to exhaust gas. For this reason, metal carriers were noisier than traditional ceramic (cordierite) carriers. In addition, there are two types of sound radiated from the metal carrier: transmitted sound passing through the outer cylinder wall and resonance sound of the outer cylinder itself.
There are ingredients. To deal with transmitted sound, it is sufficient to increase the surface density by increasing the thickness of the outer cylinder. However, if the outer cylinder is made thicker, the rigidity of the outer cylinder increases, and the frequency of the resonant sound becomes higher, which causes a problem of causing discomfort. Therefore, the present invention aims to provide a metal carrier for an automobile exhaust gas purification catalyst that can reduce noise emitted from the metal carrier and reduce unpleasant high-frequency noise.

0004

[Means for Solving the Problems] The metal carrier for an automobile exhaust gas purification catalyst of the present invention has a metal carrier in which a metal flat foil and a metal corrugated foil are overlapped and bonded and inserted into a metal outer cylinder. The outer cylinder is made of multiple layers of metal plates that are in contact with each other. The total thickness of the outer cylinder is 1.6
mm or more.

[0005] The outer cylinder is formed into a multilayer structure by overlapping a plurality of metal plates. Alternatively, one metal plate may be spirally wound and overlapped. Adjacent metal plates are in contact with each other. The number of layers is 2
~3 is practical. In the case of three layers, a metal foil may be sandwiched between two plates. As the metal foil to be sandwiched, stainless steel foil is used in consideration of heat resistance. The thickness of the outer cylinder is 1.6 m
If it is less than m, sufficient sound insulation effect cannot be obtained,
Moreover, the outer cylinder is deformed by the pressure of the high-temperature exhaust gas.

[0006]

[Operation] By increasing the thickness of the outer cylinder to 1.6 mm or more, the areal density for transmitted sound increases, and the transmitted sound is attenuated to a greater extent when passing through the outer cylinder. In addition, by making the outer cylinder into multiple layers, the damping characteristics of the outer cylinder are improved due to the friction at the interface, reducing resonance noise, and since the increase in rigidity of the outer cylinder is small, the natural frequency of the outer cylinder does not increase. The frequency of the resonant sound does not become high.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of the present invention, and is a longitudinal sectional view of a metal carrier. The metal carrier 1 is provided with a racetrack-shaped honeycomb 2. The racetrack-shaped honeycomb 2 has a spiral shape in which a flat foil 3 and a corrugated foil 4 are overlapped. The flat foil 3 and the corrugated foil 4 are brazed together. The racetrack-shaped honeycomb 2 has a racetrack-shaped outer cylinder 6
is inserted into. The racetrack-shaped outer cylinder 6 is a double cylinder consisting of an inner cylinder 7 and an outer cylinder 8. The outer circumferential surface of the racetrack-shaped honeycomb 2 and the inner circumferential surface of the inner cylinder 7 are joined by brazing.

[0008] Here, an example of measuring the sound radiated from the metal carrier will be explained. 20Cr-5A with a thickness of 50 m
A flat foil and a corrugated stainless steel foil were overlapped and rolled into a cylindrical shape. Then, this was pressed in the radial direction to produce a racetrack-shaped honeycomb (shorter diameter: 80 mm, longer diameter: 160 mm, length: 105 mm). On the other hand, a 1 mm thick 19Cr stainless steel plate was processed with ribs in advance, then formed into a racetrack shape, and the edges were welded to form an internal cylinder. In addition, 1 with a plate thickness of 1.2 mm
A 9Cr stainless steel plate was processed with ribs and formed into a racetrack shape to form an external cylinder. This outer tube was superimposed on the inner tube, and the edges of the outer tube were welded to prepare an outer tube made of two layers of stainless steel plates. Then, the honeycomb was inserted into the outer tube, and the corrugated foil, flat foil, and inner tube were brazed to each other, and then the catalyst Pt/Rh was supported on the corrugated foil. Separately, a single-layer racetrack-shaped outer cylinder having the same external dimensions as that of the above example was manufactured using a 19Cr stainless steel plate with a thickness of 1.5 mm. A similar honeycomb was inserted into this racetrack-shaped outer cylinder and brazed in the same manner as the former to form a metal carrier, which was used as a comparative example (conventional example).

[0009] Next, cones were welded to both end faces of the metal carrier produced as described above, and the cones were connected to the middle of an exhaust gas pipe of an engine. Additionally, the metal carrier was surrounded by an 800 mm square sound insulating box to prevent direct detection of engine noise. Measurement microphone on metal carrier 250
The metal carrier was placed at a position of mm, and the sound emitted from the metal carrier at each engine speed was measured. Engine speed 3000
The measurement results at rpm show that compared to the metal carrier (conventional example) in which the outer cylinder is made of stainless steel plates with a plate thickness of 1.5 mm, the outer cylinder is made of two stainless steel plates with plate thicknesses of 1.0 mm and 1.2 mm. Structured metal carrier (invention)
It was revealed that the radiated sound was reduced by 8 db. Furthermore, as a result of frequency analysis (FFT), each resonance point was shifted to the lower frequency side compared to the comparative example. Furthermore, Table 1 shows the results of measurements for several examples in which the thickness and number of layers of each layer of the outer cylinder were different. Table 1 shows engine speed 3
The radiation sound level at 000 rpm is shown in relative comparison.

0010

[Table 1]

From the measurement results shown in Table 1, the following is clear. In the case of 0.8-0.8 (2 pieces), the thickness of the outer cylinder is 1.6 mm, which is almost the same as the thickness of the conventional example, but the radiated sound is reduced by making the outer cylinder two layers. 6 db lower. The radiated sound level can also be lowered by inserting a stainless steel foil with a thickness of 0.05 mm between the inner and outer cylinders of the outer cylinder. Furthermore, adding ribs to the parallel portions of the outer cylinder is also effective in reducing the level of radiated sound.

0012

[Effects of the Invention] According to the metal carrier for an automobile exhaust gas purification catalyst of the present invention, since the outer cylinder is thickened to a total thickness of 1.6 mm or more, transmitted sound is greatly attenuated when passing through the outer cylinder. Ru. Furthermore, by forming the outer cylinder into multiple layers, the natural frequency of the outer cylinder is lowered, and the frequency of the resonant sound is lowered. As a result, the metal carrier emits less noise and less unpleasant high frequency noise.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of a metal carrier showing an embodiment of the present invention.

[Explanation of symbols]

1 Metal carrier 2 Racetrack shaped honeycomb 3 Flat foil 4 Wave foil 6 Outer cylinder 7 Internal cylinder 8 External tube

Claims (1)

[Claims] Claim 1: In a metal carrier in which a flat metal foil and a corrugated metal foil are overlapped and bonded and inserted into a metal outer cylinder, the outer cylinder is composed of multiple layers of metal plates in contact with each other, A metal carrier for an automobile exhaust gas purification catalyst, characterized in that the total thickness is 1.6 mm or more.