Power plants – Internal combustion engine with treatment or handling of... – Methods
Patent
1993-08-19
1998-09-22
Hart, Douglas
Power plants
Internal combustion engine with treatment or handling of...
Methods
60284, 60289, 60300, F01N 320
Patent
active
058097732
DESCRIPTION:
BRIEF SUMMARY
The subject invention concerns a method for catalyst emission control in vehicles comprising an engine having an inlet pipe and an exhaust pipe and wherein an electrically heated start-up catalyst and a main catalyst are placed adjacent one another in the exhaust pipe. The invention likewise concerns a device for performing the method.
New and stricter legislation, particularly in the USA, with respect to future limitations on air-pollutant emission levels makes it increasingly desirable to achieve more efficient emission control in motor vehicles. Today, catalyst emission control devices are those most commonly used. However, they are not capable of operating at their maximum purification efficiency during the vehicle cold-start period. Consequently, a large proportion of the air-polluting exhaust gases emitted from the present catalyst-equipped motor vehicles are generated during the heating-up period of the catalyst, a period which lasts until the catalyst reaches its operational temperature (approx. 250.degree. to 400.degree. C.). In the case of cold starts, this period may last several minutes and therefore creates a problem.
Catalysts of traditional type may be supplemented with an additional electrically heated start-up catalyst. A device of this kind is previously known from Patent Publication WO 89/10470. By heating the start-up catalyst electrically during the engine start-up it becomes possible to shorten the heating-up period of the catalyst package as a whole.
The subject invention provides improved purification of the exhaust gases in motor vehicles whereby the emission of pollutants may be controlled to within the stipulated levels. This is achieved by means of a method of the kind defined initially which is characterized in that in connection with the engine start-up a flow of air is supplied into the exhaust pipe through an air channel debauching upstream of the start-up catalyst, and in that this flow is interrupted at the latest when the main catalyst reaches its light-off temperature.
The invention will be described in the following with reference to one embodiment thereof and to the annexed drawing FIG. 1, showing an emission control system in accordance with the invention.
The system illustrated in the drawing figure is intended to purify the exhaust gases from a combustion engine 1, which could be either of the traditional gasoline-fuelled type, or be intended for alternative fuels such as LPG, natural gas or alcohol fuels. The engine is equipped with an inlet pipe 2 and an exhaust pipe 3. The exhaust gases from the engine 1 are conducted through a catalyst package comprising an electrically heated start-up catalyst 4 and a main catalyst 5 which is connected to the start-up catalyst. The main catalyst 5 is of standard type, consisting e.g. of a round ceramic substrate 4.66".times.6", 400 cpsi (cpsi=cells per square inch), with a PM loading of 50 g/ft.sup.3 (PM=precious metal) and a relationship Pt/Rh of 5:1. The start-up catalyst 4 is mounted upstream of the main catalyst 5 at a distance therefrom amounting to 0.1-5 times, and preferably 1.5-2.0 times, the length of the support structure of the start-up catalyst, in order to achieve favourable flow and temperature conditions.
The start-up catalyst 4 comprises a tubular metal catalyst-coated housing (e.g. having a diameter of 90 cm, a length L of 28 cm, 200 cpsi, with a PM loading of 60 g/ft.sup.3 and a relationship Rt/Rh of 5:1) of a particularly heat-resistant nature. The catalyst support inside the metal housing acts as a resistive load which may be connected to a source of current for heating.
In addition, the start-up catalyst is connected to a battery 6 which as a rule is the normal vehicle starter battery. In some cases, the normal vehicle starter battery capacity is insufficient for the current needs of the start-up catalyst 4, in which case a separate electric energy supply system may be required.
To connect the start-up catalyst 4 to the source of current, an electronic switch 7 is inserted between the catalyst 4 and the bat
REFERENCES:
patent: 3503716 (1970-03-01), Berger
patent: 4125997 (1978-11-01), Abthoff et al.
patent: 4976929 (1990-12-01), Cornelison et al.
patent: 5155995 (1992-10-01), Kinnear
patent: 5319929 (1994-06-01), Cornelison
AB Volvo
Hart Douglas
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