JP3713817B2 - Catalytic converter - Google Patents

Description

[0001]
【Technical field】
The present invention relates to a catalytic converter installed in an exhaust path of an automobile engine.
[0002]
[Prior art]
Conventionally, as a catalytic converter installed in an exhaust path of an automobile engine, for example, as disclosed in Japanese Patent Application Laid-Open No. 58-165516, it is provided between a carrier and an outer cylinder for housing the carrier. And an intermediate member having elasticity. As the carrier, a ceramic honeycomb carrier is generally used. The outer cylinder is made of a heat-resistant metal material.
[0003]
On the surface of the ceramic honeycomb carrier, Pt, Rh, Pd, etc. for converting harmful components such as CO, HC and NOx contained in the exhaust gas discharged from the automobile engine into harmless gas or water. A noble metal catalyst is supported.
As the material of the carrier, cordierite ceramic (2MgO.2Al ₂ O ₃ .5SiO ₂ ) is generally used, and this material has a smaller thermal expansion coefficient than that of a metal outer cylinder.
[0004]
Therefore, when the catalytic converter is heated by the exhaust gas flowing from the automobile engine, in the radial direction of the converter due to the difference in thermal expansion between the ceramic honeycomb carrier and the metal outer cylinder. , An increase in the distance between the carrier and the outer cylinder occurs. The intermediate member has an elastic force that can absorb the increase in the interval, and the ceramic honeycomb carrier is held inside the outer cylinder by the intermediate member.
[0005]
By the way, the intermediate member may be scattered when directly exposed to high-temperature (about 800 ° C.) exhaust gas.
Therefore, conventionally, as shown in, for example, Japanese Patent Laid-Open No. 56-47619, a retainer is joined to the outer cylinder, which is used as an exhaust gas shielding plate for the intermediate member, and the intermediate member is protected by the retainer. .
[0006]
[Problems to be solved]
In recent years, in order to be able to purify exhaust gas immediately after engine startup, there is a strong tendency to place a catalytic converter closer to the combustion chamber of the engine. This is to quickly raise the temperature of the carrier carrying the catalyst from a cold state before starting the engine to a temperature of 300 ° C. to 350 ° C. or more, which is the reaction temperature of the catalyst.
However, for the purpose as described above, when the catalytic converter is disposed nearer to the combustion chamber of the engine, for example, directly below the exhaust manifold, the maximum temperature of the exhaust gas flowing in at a high engine load is 800 to 900 ° C. or higher. Also become.
[0007]
Incidentally, as described above, the retainer is responsible for preventing the intermediate member from being scattered by the exhaust gas. That is, the exhaust gas directly hits the retainer.
Therefore, at the time of high engine load as described above, high temperature exhaust gas of 800 ° C. or higher is directly sprayed onto the retainer. On the other hand, the outer cylinder to which the retainer is joined is cooled at the outside air temperature, so that a large temperature difference occurs between the retainer and the outer cylinder.
[0008]
The retainer is mechanically joined to the outer cylinder or a flange provided on the outer cylinder. Alternatively, it is integrally formed with the outer cylinder or the flange.
Therefore, a temperature difference is generated between the retainer and the outer cylinder, and a difference in thermal expansion occurs between them. Therefore, a thermal stress is generated between the two, and the retainer may be deformed due to the thermal stress.
When such a deformation occurs, the retainer presses the fragile carrier, destroys the carrier, or the retainer mounting position shifts, and the intermediate member is exposed to the exhaust gas. There is a possibility that the intermediate member may be scattered by the gas.
[0009]
In view of such problems, the present invention is intended to provide a catalytic converter in which exhaust gas does not flow into the intermediate member, the intermediate member does not scatter, and the retainer is deformed and the carrier is not damaged. To do.
[0010]
[Means for solving problems]
The invention of claim 1 is a catalytic converter disposed in an exhaust path of an engine, and the catalytic converter has a carrier, an outer cylinder for housing the carrier, and elasticity provided between the two. An intermediate member;
A retainer disposed between the end of the intermediate member and the outer cylinder for preventing exhaust gas from flowing into the intermediate member;
The retainer and the outer cylinder are made of different members, and both are in a non-bonded state,
The intermediate member holds the entire circumference of the carrier in the outer cylinder, the intermediate member is longer than the axial length of the carrier , and the retainer is pressed against the outer cylinder by the elastic force of the intermediate member. It is in the catalytic converter characterized by being characterized.
[0011]
The operation of the present invention will be described below.
In the catalytic converter according to the present invention, the retainer and the outer cylinder are configured as separate members, and both are in contact with each other in a non-joined state. For this reason, even if a thermal expansion difference occurs between them, no thermal stress is generated, and therefore the retainer does not deform.
[0012]
Therefore, the retainer can always completely cover the end face of the intermediate member, the intermediate member is not directly exposed to the exhaust gas, and the scattering of the intermediate member does not occur.
Further, no thermal stress is generated in the retainer, and therefore, there is no deformation of the retainer, so that excessive force is prevented from acting on the carrier from the retainer, and the carrier is not damaged.
For this reason, the catalytic converter of the present invention can be mounted on the upstream side of the exhaust path closer to the engine as compared with the conventional product. Therefore, the temperature rising property of the carrier carrying the catalyst is improved, and the exhaust gas can be efficiently purified immediately after the engine is started.
[0013]
As described above, the present invention provides a catalytic converter in which exhaust gas does not flow into the intermediate member, the intermediate member does not scatter, and the retainer is deformed and the carrier is not damaged. Can do.
[0014]
According to a second aspect of the present invention, the retainer is preferably provided at least upstream of the engine exhaust path.
Thereby, it is possible to prevent the intermediate member from being scattered by the high-temperature exhaust gas blown from the upstream side.
At the downstream side, the exhaust gas is rectified by passing through the carrier, and the swirl velocity component in the radial direction is reduced in the exhaust gas flow. Even if the intermediate member is exposed to the exhaust gas in such a state, scattering may not occur. In this case, the downstream retainer may be omitted.
[0015]
Next, as in the invention of claim 3, it is preferable that the inner diameter of the retainer is always smaller than the outer diameter of the carrier under the operating temperature condition of the catalytic converter.
As a result, the overlapping portion of the retainer and the honeycomb carrier can be secured under the operating temperature condition of the catalytic converter, and the intermediate member can be reliably prevented from being exposed to the exhaust gas (see FIG. 1).
[0016]
Next, as in a fourth aspect of the invention, the retainer is preferably formed in an L-shaped cross section so as to cover the end of the intermediate member.
Thus, the L-shaped portion functions as a current plate, and the flow of exhaust gas blown into the retainer can be guided to blow into the carrier in a direction along the inner peripheral surface of the retainer. Therefore, it is possible to reliably prevent the exhaust gas from being blown into the intermediate member.
[0017]
According to a fifth aspect of the present invention, the outer cylinder has a conical taper portion that contracts in the longitudinal direction, while the retainer is slidably in contact with the inner surface of the taper portion. It is preferable to have a side surface.
The intermediate member is an elastic body, and the elastic force generated from the intermediate member is an axial force for holding the retainer.
[0018]
Therefore, the elastic force is converted into an centripetal force with respect to the central axis of the catalytic converter having a substantially cylindrical shape by the conical tapered portion, and the eccentricity of the retainer in the radial direction is suppressed by the centripetal force.
Thereby, a retainer and a support | carrier can be piled up reliably and it can prevent that exhaust gas blows in into the said intermediate member.
[0019]
According to a sixth aspect of the present invention, the intermediate member is preferably an alumina fiber having an Al ₂ O ₃ · SiO ₂ composition and an Al ₂ O ₃ content of 70% by weight or more.
The above-mentioned alumina fiber has a heat-resistant temperature of 1300 ° C. or higher, and until this temperature is reached, the fiber hardly undergoes crystallization and can maintain an elastic force sufficient to hold the carrier (see Embodiment 3). ).
Therefore, even when the catalytic converter is installed in a higher temperature atmosphere, the carrier does not rattle and can be held stably.
[0020]
Note that the upper limit of the Al ₂ O ₃ content is preferably 95%. If the content is higher than this value, the refining process for increasing the purity is complicated in the production of alumina fibers, which may increase the production cost.
[0021]
Conventional intermediate members are usually made of ceramic fibers containing approximately 50% by weight of Al ₂ O ₃ . Such ceramic fibers may be crystallized at a temperature of about 850 ° C., and the elastic force of the ceramic fibers may be reduced. In this case, the intermediate member could not hold the carrier and the retainer, and there was a risk that they would rattle inside the outer cylinder.
[0022]
If the retainer rattles and changes its position, exhaust gas may be blown into the intermediate member, and the intermediate member may be scattered. Further, the carrier is often made of brittle ceramic or the like, and there is a possibility that damage such as cracking or chipping may occur when the carrier rattles inside the outer cylinder.
By using the alumina fiber, it is possible to prevent such problems from occurring.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Embodiment 1
A catalytic converter according to an embodiment of the present invention will be described with reference to FIGS.
As shown in FIGS. 1 and 2, the catalytic converter 1 includes a carrier 10, an outer cylinder 11 that accommodates the carrier 10, an elastic intermediate member 12 provided therebetween, and the intermediate member 12. The retainer 2 for preventing the exhaust gas from flowing into the intermediate member 12 is disposed between the end portion 120 and the outer cylinder 11.
[0024]
The retainer 2 and the outer cylinder 11 are made of different members and are in contact with each other in a non-joined state. The retainer 2 is pressed against the outer cylinder 11 by the elastic force of the intermediate member 12. Yes.
[0025]
As shown in FIG. 1, the inner diameter d of the retainer 2 is always smaller than the outer diameter D of the carrier 10 under the operating temperature conditions of the catalytic converter 1.
As shown in FIG. 2, the retainer 2 is formed in an L-shaped cross section so as to cover the end 120 of the intermediate member 12. Further, the outer cylinder 11 has a conical taper portion 110 that contracts in the longitudinal direction, while the retainer 2 has an outer surface 219 that slidably contacts the inner surface 119 of the taper portion 110. [0026]
Hereinafter, the catalytic converter 1 will be described in detail.
As shown in FIG. 3, the catalytic converter 1 of this example is mounted on an exhaust manifold 36 that is an exhaust path of the automobile engine 3.
The carrier 2 is a thin ceramic monolith having a diameter of 71 mm, a length of 60 mm, and a wall thickness of 0.08 to 0.13 mm, and is made of a cordierite-based ceramic (2MgO · 2Al ₂ O ₃ · 5SiO ₂ ) having a low thermal expansion coefficient. .
Further, a catalyst for purifying harmful components of the exhaust gas of the engine 3 is carried on the surface of the carrier 2.
[0027]
The intermediate member 12 is made of alumina fiber (mullite fiber) with Al ₂ O ₃ of 72 wt% and SiO _{2 of} 28 wt%. One fiber diameter is 2 to 4 μm, and the thickness before being assembled to the outer cylinder is The bulk density was 15 mm and 0.08 g / cm ³ . Moreover, the thickness after assembling this to the outer cylinder was 4.5 mm, and the bulk density was 0.27 g / cm ³ .
[0028]
The outer cylinder 11 is a molded product obtained by press-forming a ferritic heat resistant stainless steel plate having a thickness of 1.5 mm into a half-divided cylindrical shape. And the diameter expansion part which comprises the center part of the catalytic converter 1 used as the outer wall which covers the said support | carrier 10 and the intermediate member 12 is internal diameter 80mm, and axial length 75mm. On the other hand, the openings 18 and 19 on the upstream side where the exhaust gas flows into the catalytic converter 1 and the downstream side where the exhaust gas flows out have an inner diameter of 70 mm and an axial length of 10 mm.
[0029]
And the taper part 110 is provided between the said diameter enlarged part 17 and the opening parts 18 and 19, respectively.
As shown in FIG. 2, the tapered portion 110 has a conical shape, and the taper angle with respect to the flow direction of the exhaust gas is approximately 60 degrees.
[0030]
The retainer 2 is provided in the openings 18 and 19 of the catalytic converter 1 and is made of ferritic heat resistant stainless steel. The inner diameter (d in FIG. 1) is 67 mm, the outer diameter is 77 mm, and the plate thickness is 1.5 mm.
The retainer 2 is disposed between the enlarged diameter portion 17 and the openings 18 and 19 of the outer cylinder 11. The taper portion 110 is held by an elastic force acting from the end surface 120 of the intermediate member 12 and is not particularly joined to the outer cylinder 11.
[0031]
Next, the arrangement state of the catalytic converter 1 in the exhaust path of the engine 3 will be described. As shown in FIG. 3, the catalytic converter 1 of this example is disposed with respect to an exhaust manifold 36 provided in the engine 3. As shown in FIG. 4, a start catalyst 21 having a capacity of 1300 cc is disposed downstream of the catalytic converter 1 in the exhaust gas flow.
The start catalyst 21 is held and fixed in a start catalyst outer cylinder 211 via a wire net or a ceramic fiber mat.
[0032]
Next, the assembly process of the catalytic converter 1 will be described with reference to FIG.
First, the intermediate member 12 is compression-molded into the same shape as the outer periphery of the carrier 10 using a binder (for example, epoxy resin), and then wound around the outer periphery of the carrier 10.
Next, the retainer 2 is pressed against the end surface 120 of the intermediate member 12.
Next, the carrier 10, the intermediate member 12, and the retainer 2 are sandwiched between semi-cylindrical steel plates 111 and 112 that can constitute the outer cylinder 11 after assembly.
[0033]
At this time, since the retainer 2 is arranged so as to cover the end surface 120 of the intermediate member 12, the semi-cylindrical steel plates 111 and 112 are assembled without biting the end surfaces of the intermediate member 12 with the semi-cylindrical steel plates 111 and 112. Can do.
Finally, the semi-cylindrical steel plates 111 and 112 are wire-welded without gaps so as not to leak the exhaust gas, thereby forming the outer cylinder 11.
Thus, the catalytic converter 1 was obtained.
[0034]
Next, the effect in this example is demonstrated.
The catalytic converter 1 according to the present example is disposed in the exhaust manifold 36. Therefore, particularly when the engine 3 is under a high load, a very high temperature exhaust gas flows in. Therefore, the retainer 2 is maintained at a high temperature by the high temperature exhaust gas.
On the other hand, since the outer cylinder 11 is cooled by the outside air temperature, it is held at a temperature lower than that of the retainer 2.
Therefore, a large temperature difference is generated between the retainer 2 and the outer cylinder 11, and thus a thermal expansion difference is generated.
[0035]
However, in this example, the retainer 2 and the outer cylinder 11 are separate parts and are not joined to each other, so that no stress is generated even if a difference in thermal expansion occurs between them.
Accordingly, the retainer 2 is prevented from being deformed, and thus the damage of the carrier 10 due to the deformation of the retainer 2 and the scattering of the intermediate member 12 due to exhaust gas can be prevented.
Thus, this example is a catalytic converter 1 that can be used even in an environment where high-temperature exhaust gas of 900 ° C. or higher flows.
[0036]
As shown in FIG. 2, the retainer 2 is formed in an L-shaped cross section so as to cover the end 120 of the intermediate member 12.
Accordingly, the L-shaped portion functions as a current plate, and the flow of exhaust gas blown into the retainer 2 can be guided to blow into the carrier 10 in the direction along the inner peripheral surface of the retainer 2. Therefore, it is possible to reliably prevent the exhaust gas from being blown into the intermediate member 12.
[0037]
As shown in FIG. 1, the inner diameter d of the retainer 2 is always smaller than the outer diameter D of the carrier under the operating temperature condition of the catalytic converter 1. Thereby, an overlapping portion can be secured between the retainer 2 and the carrier 10, and the intermediate member 12 can be reliably prevented from being exposed to the exhaust gas.
[0038]
In this embodiment, the retainers 2 are provided at two locations on the upstream side and the downstream side, respectively. However, when the flow of exhaust gas is weakened to the extent that the intermediate member 12 is not scattered by the rectifying action of the carrier 10. , One retainer 2 may be provided on the upstream side.
[0039]
Embodiment 2
This example is a low-cost catalytic converter 4 having a retainer 29 according to the present invention, as shown in FIGS.
As shown in FIG. 6, the catalytic converter 4 of the present example includes a carrier 10, an outer cylinder 41 that accommodates the carrier 10, an elastic intermediate member 12 provided between the two, and the intermediate member 12. The retainer 29 is disposed between the end portion 120 and the outer cylinder 41 to prevent the exhaust gas from flowing into the intermediate member 12.
[0040]
The retainer 29 and the outer cylinder 41 are made of different members, and both are in contact with each other in a non-bonded state. The retainer 29 is pressed against the outer cylinder 41 by the elastic force of the intermediate member 12.
The retainer 29 is provided only on the upstream side of the engine exhaust path.
[0041]
The carrier 10 has the same shape, configuration, and material as in the first embodiment.
The outer cylinder 41 is a molded product obtained by press-molding a ferritic heat resistant stainless steel plate having a thickness of 1.5 mm into a substantially cylindrical shape.
In the press forming process, first, a stainless steel plate is formed into a cylindrical shape with only one end squeezed, and the other end is squeezed into the same shape during the assembly process of the catalytic converter described later, and the inner diameter is 80 mm at the large diameter portion. The axial length is 70 mm, the opening is 70 mm, and the axial length is 10 mm.
[0042]
The retainer 29 is a molded product obtained by punching from a ferritic heat resistant stainless steel having a plate thickness of 1.5 mm into an annular shape having an inner diameter of 67 mm and an outer diameter of 77 mm.
Although the retainer 29 of this example has an annular shape, the retainer 29 may be configured by combining two half-shaped molded products.
The intermediate member 12 is made of the same material as that of the first embodiment.
[0043]
Next, the assembly process of the catalytic converter 4 will be described with reference to FIG.
First, the intermediate member 12 is compression-molded into a shape similar to the outer peripheral shape of the carrier 10 using a binder (for example, epoxy resin), and then wound around the outer periphery of the carrier 10.
Next, the retainer 2 is pressed against one end surface 120 of the intermediate member 12.
[0044]
Next, as shown in FIG. 7, the carrier 10, the intermediate member 12, and the retainer 205 are all pressed into the outer cylinder 41 from the end surface 120 opposite to the end surface against which the retainer is pressed.
Thereafter, the unmolded end portion of the outer cylinder 41 is drawn from the upper portion of the retainer 29 so as to have an inner diameter of 67 mm. Thus, the catalytic converter 4 was obtained.
Others are the same as the first embodiment.
[0045]
According to the present invention, an annular retainer 29 is provided only on the upstream side of the engine exhaust path, and a catalytic converter 4 having a low cost configuration with four components can be obtained.
The other functions and effects are the same as those of the first embodiment.
[0046]
Embodiment 3
In this example, as shown in FIGS. 8 and 9, the performance of the alumina fiber used for the intermediate member in the first and second embodiments will be described.
The composition of the alumina fiber is 72 wt% for Al ₂ O _{3 and} 28 wt% for SiO ₂ .
The alumina fiber was compressed to a predetermined bulk density in a temperature environment of 25 ° C. and 1000 ° C. The thickness before compression is 15 mm, and the bulk density is 0.08 g / cm ³ , which corresponds to the state before being assembled in the outer cylinder in the above embodiment.
[0047]
FIG. 8 shows the relationship between the elastic force acting per unit area of the alumina fiber, that is, the surface pressure and the thickness of the alumina fiber after compression.
The surface pressure was measured by transmitting the elastic force changing with compression to a load cell set outside the high-temperature atmosphere furnace using a ceramic compression rod.
[0048]
According to the figure, the surface pressure of the alumina fiber is about the same at 25 ° C. and 1000 ° C.
That is, it was found that the surface pressure of the alumina fiber remained stable even when the temperature changed.
[0049]
Next, the X-ray diffraction result of the alumina fiber is shown in FIG.
According to the figure, the diffraction result of the alumina fiber has the same shape in both cases of 25 ° C. and 1000 ° C. This indicates that the crystal structure of the alumina fiber does not change when the alumina fiber is either 25 ° C. or 1000 ° C.
[0050]
From the above, it has been found that when the alumina fiber is used as the intermediate member, the carrier can be stably held under any temperature environment, particularly in a high temperature atmosphere of 900 ° C. or higher.
[Brief description of the drawings]
FIG. 1 is a cross-sectional explanatory view of a catalytic converter in Embodiment 1;
FIG. 2 is a cross-sectional explanatory view of a main part of the catalytic converter in the first embodiment.
FIG. 3 is an explanatory diagram illustrating how the catalytic converter is attached to the engine in the first embodiment.
4 is a partial cross-sectional view of the catalytic converter and the start catalyst in Embodiment 1. FIG.
FIG. 5 is a development view of the catalytic converter in the first embodiment.
6 is a cross-sectional explanatory view of a catalytic converter in Embodiment 2. FIG.
7 is an explanatory diagram of assembly of a catalytic converter in Embodiment 2. FIG.
FIG. 8 is an explanatory diagram showing the relationship between the surface pressure of alumina fibers and the thickness after compression of alumina fibers in Embodiment 3;
9 is an explanatory diagram of an X-ray diffraction intensity distribution of alumina fiber in Embodiment 3. FIG.
[Explanation of symbols]
1,4. . . Catalytic converter,
10. . . Carrier,
11, 41. . . Outer cylinder,
12 . . Intermediate members,
120. . . edge,
2,29. . . Retainer,
110. . . Taper,

Claims (6)

A catalytic converter disposed in an exhaust path of an engine, the catalytic converter comprising a carrier, an outer cylinder for housing the carrier, an elastic intermediate member provided between the two,
A retainer disposed between the end of the intermediate member and the outer cylinder for preventing exhaust gas from flowing into the intermediate member;
The retainer and the outer cylinder are made of different members, and both are in a non-bonded state,
The intermediate member holds the entire circumference of the carrier in the outer cylinder, the intermediate member is longer than the axial length of the carrier , and the retainer is pressed against the outer cylinder by the elastic force of the intermediate member. Catalytic converter characterized by being made.   2. The catalytic converter according to claim 1, wherein the retainer is provided at least upstream of the engine exhaust path.   3. The catalytic converter according to claim 1, wherein an inner diameter of the retainer is always smaller than an outer diameter of the carrier under a use temperature condition of the catalytic converter.   4. The catalytic converter according to claim 1, wherein the retainer is formed in an L-shaped cross section so as to cover an end of the intermediate member.   5. The outer cylinder according to claim 1, wherein the outer cylinder has a conical taper portion that contracts in the longitudinal direction, while the retainer slidably contacts the inner surface of the taper portion. A catalytic converter having an outer surface. The intermediate member according to any one of claims 1 to 5, wherein the intermediate member is an alumina fiber having an Al ₂ O ₃ · SiO ₂ composition and an Al ₂ O ₃ content of 70 wt% or more. Catalytic converter.

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