Power plants – Internal combustion engine with treatment or handling of... – By means producing a chemical reaction of a component of the...
Reexamination Certificate
2000-09-20
2002-10-22
Denion, Thomas (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
By means producing a chemical reaction of a component of the...
C060S274000, C060S280000, C060S297000
Reexamination Certificate
active
06467258
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method for control of a combustion engine and the arrangement of a combustion engine having means for generation of an air/fuel mixture to each cylinder of the engine, an exhaust system which is connected to the engine, an exhaust catalyst and a NO
x
adsorbent which are provided in the exhaust system thereof. The invention is particularly intended for use in the field of regeneration of a NO
x
adsorbent which is arranged in connection with a combustion engine. In a particularly preferred embodiment, the invention takes the form of a device for control of a combustion engine including means for generation of an air/fuel mixture to each cylinder of the engine, an exhaust system which is connected to the engine, an exhaust catalyst and a NO
x
adsorbent which are provided in the exhaust system. The generating mean(s) are adapted to assume: a first operating condition that delivers a comparatively lean exhaust gas mixture to the NO
x
adsorbent for adsorption of NO
x
compounds in the exhaust gas mixture; and a second operating condition that delivers a comparatively rich exhaust gas mixture to the NO
x
adsorbent for desorption of NO
x
compounds in the exhaust gas mixture.
BACKGROUND OF THE INVENTION
In the field of vehicles which are operated by combustion engines, there is a general demand for low emissions of harmful substances in the exhaust gases from the engine. These substances are primarily considered to be pollutants and often take the form of nitrogen oxide compounds (NO
x
), hydrocarbon compounds (HC), and carbon monoxide (CO). Regards today's petrol engines, the exhaust gases are normally purified by means of an exhaust catalyst, which forms part of the exhaust system and through which the exhaust gases are guided. In what is often referred to as a three-way catalyst, which is previously known, the major part of the above-mentioned harmful compounds are eliminated by catalytic reactions. In order to optimize the function of the catalyst so that it provides an optimal degree of purification for NO
x
, HC, and CO, the engine is in most operating cases operated by a stoichiometric air/fuel mixture, i.e. a mixture where &lgr;=1.
Although today's three-way catalysts normally have a very high degree of purification which strongly reduces the emissions of harmful pollutants into the atmosphere, there are demands today for additional reductions of the emissions of such harmful substances. These demands originate from among other things, increasingly strict legislation in various countries, with associated demands for extremely low emissions of NO
x
, CO, and HC compounds.
Furthermore, in the field of vehicles, there is a general demand for reducing the fuel consumption of the engine to the highest possible degree. To this end, during the last few years, engines have been developed having new types of combustion chambers in the engine's cylinders, particularly in order for the engine to be able to be operated by increasingly lean fuel mixtures, i.e. where &lgr;=1. Such engines are generally termed “lean-burn” engines. In one type referred to as a DI engine (i.e. a direct-injected Otto cycle engine), the respective combustion chamber in the engine is constructed in such a manner that the supplied fuel can be concentrated to a high degree at the respective spark plug. During continues driving, such engines can be operated by a very lean air/fuel mixture, approximately &lgr;=4. For this reason, a substantial savings in fuel consumption is obtained using this type of engine.
Due to the fact that a DI engine is normally operated by a very lean air/fuel mixture, a correspondingly lean exhaust gas mixture will flow through the three-way catalyst. This results in the three-way catalyst being unable to reduce the NO
x
compounds in the exhaust gases (due to the fact that it is constructed for an optimal degree of purification for a stoichiometric mixture). For this reason, a conventional three-way catalyst can be combined with a nitrogen oxide adsorbent (also called NO
x,
adsorbent, or “NO
x
trap”), which is a per se a known device, for absorption of NO
x
compounds, e.g. in the exhaust gases from a combustion engine. In this manner, the NO
x
adsorbent can be installed and utilized as a complement to a conventional three-way catalyst.
A NO
x
adsorbent can be arranged either as a separate unit upstream of a conventional three-way catalyst, or alternatively as an integral part of the three-way catalyst, i.e. together with the catalytic material of the three-way catalyst. The NO
x
adsorbent is constructed in such a manner that it takes up (adsorbs) NO
x
compounds from the exhaust gases if the engine is operated by a lean air/fuel mixture and gives off (desorbs) NO
x
compounds if the engine is operated by a rich air/fuel mixture during a certain time period. Furthermore, the NO
x
adsorbent has the property of being able only to adsorb NO
x
compounds up to a certain limit, i.e. it is eventually “filled” and thus reaches a limit for adsorption. In this situation, the NO
x
adsorbent must be regenerated, i.e. it must be influenced to desorb, and thus to release the accumulated NO
x
, compounds. If a conventional three-way catalyst is arranged downstream of the NO
x
adsorbent, the desorbed NO
x
compounds can be eliminated by means of the three-way catalyst, provided that the latter has reached its ignition temperature.
According to known designs, the regeneration of the NO
x
adsorbent can be accomplished by making the exhaust gas mixture through the NO
x
adsorbent comparatively rich during a certain time period, which in turn can be achieved by means of the engine being operated by a comparatively rich air/fuel mixture for a short time period, e.g. a few seconds. In this manner, the NO
x
adsorbent is “emptied” so that it thereafter can adsorb NO
x
compounds during a certain time period which lasts until a new regeneration becomes necessary.
Such regeneration is known to be obtainable by means of a control of the air concentration in the exhaust gas mixture through the NO
x
adsorbent. A system for such a control is disclosed in the U.S. Pat. No. 5,461,857 which discloses an engine having an exhaust gas filter system that in turn comprises a three-way catalyst, an oxidation catalyst and a NO
x
adsorbent. According to this known system, an air/fuel mixture is combusted in the engine's combustion chamber, wherein the exhaust gases from the engine are fed through the three-way catalyst in a known manner. Furthermore, the system contains an air pump for supplying secondary air to the exhaust pipe at a position between the three-way catalyst and the NO
x
adsorbent. By means of the supply of secondary air, the exhaust gas mixture through the NO
x
adsorbent can be made lean. In this manner, the reduction of the NO
x
compounds in the exhaust gases takes place in two steps, i.e. in the three-way catalyst, as well as in the NO
x
adsorbent. In such a system, the NO
x
adsorbent can be regenerated by interruption of the supply of the secondary air. This provides a pulse with a comparatively rich exhaust gas mixture to the NO
x
adsorbent, by means of which it is regenerated.
Although this known system in principle operates satisfactorily, it has, however, certain drawbacks. Primarily, in can be noted that the system requires a number of different constructional details to supply the secondary air (i.e. a secondary air pump, air conduits, valves, and connections for the air conduits to the exhaust system). These components must be assembled in connection with the engine, which causes the system to become unnecessarily expensive as regards the cost for the components, as well as for its assembly in the vehicle in question.
Another drawback relates to the fact that the driver of the vehicle normally perceives this regenerative process disadvantageous to comfort if the NO
x
adsorbent is regenerated too often. This results because the production of rich exhaust gas pulses can be perceived as “jer
Jobson Edward
Lundgren Staffan
Sandberg Lars
AB Volvo
Brehob Diana D.
Denion Thomas
Howrey Simon Arnold & White , LLP
Lippe Allan J.
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