1. Field of Invention
The present invention relates to a system and a method for improving performance of a NOx-reducing catalyst and, more particularly, to controlling an amount of reductant injection to achieve optimum NOx conversion efficiency while minimizing the fuel economy penalty.
2. Background of the Invention
Current emission control regulations necessitate the use of catalysts in the exhaust systems of automotive vehicles in order to convert carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx) produced during engine operation into harmless exhaust gasses. Vehicles equipped with diesel or lean gasoline engines offer the benefits of increased fuel economy. Such vehicles have to be equipped with lean exhaust aftertreatment devices, such as, for example, an Active Lean NOx Catalysts (ALNC) or Selective Catalytic Reduction (SCR) catalysts, which continuously reduce NOx emissions, even in an oxygen rich environment, through active injection of reductant, such as fuel (HC) or urea, into the exhaust gas entering these devices. Further, it is important to precisely control the amounts of reductant in order to achieve maximum NOx conversion efficiency.
The inventors herein have recognized that transient changes in engine operating conditions cause changes in engine feedgas NOx production. For example, NOx production usually increases during engine acceleration, and decreases during deceleration. Since the amount of reductant injection is typically calculated based on steady state engine operating conditions, these transient NOx variations result in over or under-injection of reductant and negatively impact fuel economy and emission standards.
In accordance with the present invention, a system and a method for controlling an amount of reductant to be delivered to a NOx-reducing catalyst are presented. The method includes calculating a desired amount of reductant based on a measure of engine transient behavior; and injecting said calculated desired amount of reductant into the NOx-reducing catalyst.
In one aspect of the present invention, the device is an ALNC and the reductant is hydrocarbon. In another aspect of the present invention, the device is an SCR catalyst and the reductant is urea. In yet another aspect of the present invention, the measure of engine transient behavior is a measure of engine acceleration. In another aspect of the present invention, the measure further includes engine deceleration. In another aspect of the present invention, the measure of engine transient behavior is based on a rate of change of pedal position. In yet another aspect of the present invention, the measure of engine transient behavior is based on a rate of change of engine fuel injection amount. In yet another aspect of the present invention, the measure of engine transient behavior is based on a rate of change of engine speed.
In another aspect of the present invention, a method for improving efficiency of a NOx-reducing catalyst coupled downstream of an internal combustion engine includes: providing an indication of an impending engine transient; and adjusting an amount of reductant injection into the NOx-reducing catalyst to compensate for variations in engine feedgas NOx caused by said impending engine transient.
The present invention provides a number of advantages. In particular, NOx conversion efficiency of the NOx-reducing catalyst is improved by adjusting the injected reductant amounts to compensate for transient increases or decreases in the engine feedgas NOx amounts. Further, monitoring the rate of change of pedal position provides a quick and accurate indication of an impending engine transient and the associated change in engine feedgas NOx. Thus, reductant injection amount can be timely adjusted to compensate for NOx variations. Another advantage of the present invention is improved fuel economy due to optimized reductant usage. For example, reductant injection amount can be reduced in anticipation of engine deceleration to compensate for a reduction in engine feedgas NOx.
The above advantages and other advantages, objects and features of the present invention will be readily apparent from the following detailed description of the preferred embodiments when taken in connection with the accompanying drawings.
The objects and advantages described herein will be more fully understood by reading an example of an embodiment in which the invention is used to advantage, referred to herein as the Description of Preferred Embodiment, with reference to the drawings, wherein:
Internal combustion engine 10, comprising a plurality of cylinders, one cylinder of which is shown in
Controller 12 is shown in
Oxidation catalyst 13 is coupled to the exhaust manifold 48 downstream of engine 10 and may be a precious metal catalyst, preferably one containing platinum. Catalyst 14, a NOx-reducing catalyst capable of reducing NOx in an oxygen rich environment, is coupled downstream of the oxidation catalyst. In a preferred embodiment Catalyst 14 is an Active Lean NOx Catalyst (ALNC) comprising a precious metal or a combination of precious metals, such as Platinum or Palladium, an acidic support material, such as the one containing alumina and silica, and a zeolite material. In an alternative embodiment, catalyst 14 may be a urea-based Selective Catalytic Reduction (SCR) catalyst, which is a device comprising some or all of the features of the ALNC catalyst and optimized for use with urea or other ammonia-based compounds as reductant. The oxidation catalyst 13 exothermically combusts hydrocarbons (HC) in the incoming exhaust gas from the engine thus supplying heat to rapidly warm up catalyst 14. Additionally, carbon monoxide (CO) produced as a result of HC combustion in the oxidation catalyst 13 improves NOx reduction in the catalyst 14.
A reductant delivery system 16 is coupled to the exhaust gas manifold between the oxidation catalyst and the NOx-reducing catalyst and is described in more detail in
Referring now to
The diagram of
As will be appreciated by one of ordinary skill in the art, the routines described in
Referring now to
The routine then proceeds to step 800 wherein the rate of change of pedal position is computed as follows:
In an alternative embodiment (not shown), the modified steady-state reductant injection amount,
Therefore, according to the present invention, in order to achieve a more efficient NOx-reducing catalyst performance, the amount of reductant to be injected should be adjusted to account for increases and decreases in the amount of NOx in the exhaust gas entering the catalyst. This can be accomplished by continuously monitoring engine parameters that are capable of providing a measure of engine transient behaviors, and continuously adjusting the amount of reductant to be injected as a function of these parameters. Since NOx production typically increases at tip-in and decreases at tip-out, the result of such operation would be to increase the base injected amount in the former case, and decrease the base injected amount in the latter case. By monitoring parameters that are capable of providing very quick indication of engine transients, such as, for example, rate of change of pedal position, rate of change of engine fuel injection amount, or rate of change of engine speed or load, it is possible optimize system response and ensure that optimal reductant amount is timely injected into the device in response to a change in engine feedgas NOx.
This concludes the description of the invention. The reading of it by those skilled in the art would bring to mind many alterations and modifications without departing from the spirit and the scope of the invention. Accordingly, it is intended that the scope of the invention be defined by the following claims:
Number | Date | Country | |
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Parent | 10065650 | Nov 2002 | US |
Child | 10949479 | Sep 2004 | US |