Chemical apparatus and process disinfecting – deodorizing – preser – Chemical reactor – Waste gas purifier
Reexamination Certificate
2000-06-05
2004-11-30
Tran, Hien (Department: 1764)
Chemical apparatus and process disinfecting, deodorizing, preser
Chemical reactor
Waste gas purifier
C422S177000, C422S180000, C029S890000
Reexamination Certificate
active
06824744
ABSTRACT:
BACKGROUND OF THE INVENTION
A standard catalytic converter, especially for motor vehicles, comprises a metal housing with a catalytic converter element positioned on the inside. A ceramic catalytic converter element, in the following called a monolith, has a far lower stability than a metallic one. In addition, the heat expansion coefficients of the ceramic material and the metallic housing are very different. The monolith is therefore positioned inside the housing with the aid of a positioning mat, which is inserted with pre-stressing into a gap between monolith and housing. So-called expanding mats are frequently used as positioning mats. These are mineral-fiber mats with exfoliated mica particles embedded therein. Exfoliated mica irreversibly hydrolyzes water vapor at increased temperatures, thereby causing the particles to change to an expanded state. In the expanded state of the exfoliated mica particles, the mat exerts higher restoring forces in radial direction onto the inside surface of the housing and the peripheral surface of the monolith, which is linked to an increase in the ejection force. The ejection force is understood to be the force with which the monolith must be admitted in axial direction to remove it from its positioning or to displace it in axial direction. For understandable reasons, the ejection force should be as high as possible to ensure a reliable positioning of the monolith during the vehicle operation.
Positioning mats that do not contain exfoliated mica are used in addition to expanding mats. Mats of this type essentially consist only of mineral fibers. The radial restoring forces of both mat types are generated in that the thickness of the mat in the uninstalled condition exceeds the gap measure for the gap space between monolith and housing. Whereas the gap enlargement for expanding mats during the operating temperatures of the catalytic converter is balanced out by the expansion of the exfoliated mica particles, the radial pre-stressing of the positioning mat of mineral fibers without exfoliated mica must be high enough to ensure that the monolith is positioned securely, even in the expanded state of the gap. As a rule, the intent is to have the smallest possible gap measure for the gap space in order to increase the restoring forces of a mat with a specified thickness. With housings consisting of two shell halves, a monolith packet consisting of one or several monoliths wrapped with a positioning mat, is initially inserted into one half shell and the second half shell is then fitted on. In the process, the positioning mat must be compressed to the thickness corresponding to the desired gap measure. While a monolith is relatively insensitive to a radially effective isostatic load, there is danger that the monolith is destroyed during the shearing stress that may result from a tangential force introduction. With a housing consisting of two shell halves, a shearing stress of this type occurs mainly along the edges of the half shells. Thus, relatively narrow limits are set for reducing the gap measure of a catalytic converter of this type. The same is true for catalytic converters having a wrap-around housing. A third type of catalytic converter design uses a tube section for the part of the housing where the monolith or monoliths are located. For the production of such catalytic converters, the above-mentioned monolith packet is pressed into a tube section. The restoring forces generated by the compression of the positioning mat in the process uniformly act upon the peripheral region of the monolith, meaning they have a quasi isostatic effect on the monolith. A shearing stress virtually does not occur. Nevertheless, the gap space in traditional tube-shaped catalytic converters cannot be reduced to a satisfactory degree for increasing the mat restoring forces. The reason for this is that pressing the monolith packet into a tube section becomes proportionally more difficult the smaller the available gap space or the greater the positioning mat thickness that exceeds the available gap measure for the gap space.
SUMMARY OF THE INVENTION
Starting with this, it is the object of the invention to suggest a catalytic converter with improved positioning of the monolith, as well as a method for producing a catalytic converter with a tubular design.
This object is solved with a method and catalytic converter according to the present invention. If reference is made to an approximately cylindrical tube section or an approximately cylindrical monolith, this also includes oval or polygonal tube sections and monoliths. In addition, a catalytic converter in general is understood to mean a device for cleaning exhaust gases, which can additionally or instead of a monolith include a particle filter or a soot filter. For a method according to the invention, a tube section with several different cross-sectional surfaces on the inside is provided, wherein a monolith packet is pressed in from a tube end with a larger or the largest inside cross-sectional surface or clear width. For example, a tube section can be selected, which has a first longitudinal section with larger inside cross-sectional surface and an adjoining second longitudinal section with smaller inside cross-sectional surface. The larger inside cross-sectional surface is selected such that the insertion of the monolith packet will not present any problems. However, the positioning mat is still compressed to generate the restoring forces. The subsequent longitudinal section with smaller inside cross-sectional surface, on the other hand, is selected so that the highest possible compression of the positioning mat occurs, thus generating the highest possible restoring forces. In contrast, the use of a tube section with on the whole reduced inside cross-sectional surface would engender the danger of the positioning mat getting snagged at the beginning of the pressing-in action, e.g. in the frontal region of the tube section, and that only the monolith would be pushed farther into the tube section. However, if a larger inside cross-sectional surface and accordingly a gap with larger gap measure exist at the pressing-in end of the tube section, the monolith packet can be pressed into the tube section without a change in the desired position of the positioning mat, relative to the monolith. If the front end of the monolith packet that points in pressing-in direction later enters the longitudinal tube section with reduced cross section, the region in front of the positioning mat is already stabilized sufficiently by the tube section, so that a change in the desired mat position is prevented. A tube section pre-manufactured in this way is arranged such that the narrowed longitudinal section encloses the frontal region of the monolith that points toward the inflow funnel.
The production of a catalytic converter according to the invention can also occur such that a monolith packet is pressed from each tube end into the tube section. In that case, both tube ends have a larger cross sectional inside surface than at least one region, arranged in-between, with reduced cross sectional inside surface. It is preferable if a tube section is used, for which the inside cross-sectional surface is reduced in stages, in the form of several longitudinal sections, wherein the inside surface of the respective longitudinal sections extends parallel to the central longitudinal axis of the tube section. In other words, the inside surface of the respective longitudinal section forms a cylinder jacket with circular, oval or polygonal periphery, which extends coaxial to the central longitudinal axis of the tube section. For one embodiment variant, the successive longitudinal sections in pressing-in direction are arranged in the order of decreasing inside cross-sectional surfaces. The positioning mat is compressed more and more with increasing depth for pressing in, until it experiences the highest compression at the end of the pressing-in operation, in the region of the tube end pointing in pressing-in direction.
As alternative to a tube
Buckel Thomas
Stoepler Walter
Faurecia Abgastechnik GmbH
Kinberg Robert
Tran Hien
Venable LLP
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