Device for catalytic purification of exhaust gases

Power plants – Internal combustion engine with treatment or handling of... – By means producing a chemical reaction of a component of the...

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Details

60302, 60301, 422180, F01N 310

Patent

active

059963395

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The present invention relates to a catalytic exhaust gas purification arrangement.


BACKGROUND OF THE INVENTION

Catalytic exhaust gas purifiers are often used in motor vehicles in order to purify the exhaust gases from the vehicle's engine. However, present catalytic converters (catalyzers) are not able to operate at full purification efficiency in connection with cold-starting of a vehicle. This problem can be overcome by arranging an additional, electrically-heatable start catalyzer in front of the ordinary catalyzer. By heating up the start catalyzer electrically, the warm-up time for the ordinary catalyzer can be shortened, which results in improved purification efficiency during cold starts. Such a catalyzer arrangement is shown in International Patent No. WO 80/10470.
A problem which occurs in connection with an electrically-heatable start catalyzer is that it requires a powerful electrical supply in order to be activated. This can, for example, be achieved by arranging an additional battery in the vehicle, which is however unnecessarily expensive and complicated. It is therefore desirable to have a catalyzer arrangement which is not dependent on an electrical supply, but which still produces a shortening of the main catalyzer's "ignition" time (the so-called "light-off" time), i.e. the time which elapses from starting the engine until the catalyzer is working at optimal purification efficiency. This should, in such a case, result in improved purification efficiency of the entire catalyzer arrangement.
In connection with conventional catalyzers, there is an additional problem in that the incoming exhaust gases impinge directly onto the catalyzer. This produces a turbulent flow immediately in front of the catalyzer, which leads to inefficient operation of the catalyzer as well as a comparatively high back-pressure, which is a disadvantage compounding the reduction in the efficiency of the catalyzer. One way of solving this problem is to direct the exhaust gases at an angle to the catalyzer, for instance in accordance with the disclosure in European Patent No. 420,462. This arrangement, however, presents a disadvantage in that it has relatively poor flow characteristics, since not only the inlet but also the outlet are angled with respect to the catalyzer.
A main object of the present invention is to solve the aforementioned problems and provide an improved arrangement for catalytic exhaust gas purification, in particular for shortening the light-off time of such an arrangement.
An additional object of the present invention is to achieve a correct measurement of the conversion efficiency of the aforementioned catalyzer arrangement, in order to provide information for a diagnosis of its operation. This allows an indication, e.g. in the form of a warning light, which warns the vehicle driver that the catalyzer is defective and has to be replaced.


SUMMARY OF THE INVENTION

In accordance with the present invention, these and other objects have now been realized by the invention of apparatus for the catalytic purification of exhaust gases which comprises a housing, an inlet for supplying the exhaust gases to the housing, the inlet having a first end distal from the housing and a second end proximate to the housing, a first catalyzer unit having a first cross-sectional area located within the housing adjacent to the second end of the inlet, the first catalyzer unit having a longitudinal axis, and a second catalyzer unit having a second cross-sectional area located within the housing downstream of the first catalyzer unit, the first cross-sectional area being less than the second cross-sectional area, the second end of the inlet being disposed at an angle with respect to the longitudinal axis of the first catalyzer unit. Preferably, the apparatus includes a third catalyzer unit located within the housing downstream of the second catalyzer unit.
In accordance with one embodiment of the apparatus of the present invention, the second catalyzer unit has a substantially oval cross-secti

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Automotive Engineering, SAE International, Sep. 1994, Convergence '94 Show Issue, Heated Catalytic Converter.
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State of California, Air Resources Board, Staff Report: Initial Statement of Reasons for Rulemaking, Ford Motor Company's Petition for Limited Relief from 1994/1995 On-Board Diagnostic II (OBD II) Provisions, May 21, 1993.

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