Lean catalyst and particulate filter control

#The present invention relates to a system and method for controlling an engine having both a lean NOx catalyst for reducing exhaust NOx in an oxygen rich environment and a particulate filter for removing carbon particles, or soot.

#In order to meet future emission regulations in vehicles having a compression ignition engine, it may be necessary to use lean NOx catalysts in combination with particulate filters.

#A NOx catalyst reduces NOx emissions continuously, even in an oxygen rich environment. For an active NOx catalyst to maximize NOx reduction, a reducing agent, for example, diesel fuel or urea, needs to be present. The optimum amount of reducing agent for the NOx catalyst is typically based on engine operating conditions and catalyst conditions. These conditions typically include engine speed, engine load, and catalyst temperature.

#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:

#FIGS. 1A and 1B schematic diagrams of an engine wherein the invention is used to advantage; and

#FIGS. 2-7 are high level flow charts of various operations performed by a portion of the embodiment shown in FIGS. 1A and 1B.

#Internal combustion engine 10, comprising a plurality of cylinders, one cylinder of which is shown in FIG. 1A, is controlled by electronic engine controller 12. Engine 10 includes combustion chamber 30 and cylinder walls 32 with piston 36 positioned therein and connected to crankshaft 40. Combustion chamber 30 is known communicating with intake manifold 44 and exhaust manifold 48 via respective intake valve 52 and exhaust valve 54. Intake manifold 44 is also shown having fuel injector 80 coupled thereto for delivering liquid fuel in proportion to the pulse width of signal FPW from controller 12. Both fuel quantity, controlled by signal FPW and injection timing are adjustable. Fuel is delivered to fuel injector 80 by a diesel fuel system (not shown) including a fuel tank, fuel pump, and fuel rail (not shown). Alternatively, the engine may be configured such that the fuel is injected directly into the cylinder of the engine, which is known to those skilled in the art as a direct injection engine.

#Reducing agent, for example, ammonia or diesel fuel, is stored in storage vessel 130 coupled to exhaust manifold 48 upstream of particulate filter 95 and lean NOx catalyst 97. In an alternative embodiment (not show) diesel fuel can be stored solely in the fuel tank and supplied to the exhaust system. Also, catalyst 97 is lean NOx catalyst capable of reducing NOx in an oxygen rich environment. Efficiency of catalyst 97 is increased in the presence of a reducing agent.

#Control valve 134 controls the quantity of reducing agent delivered to the exhaust gases entering catalyst 97. Pump 132 pressurizes the reducing agent supplied to control valve 134. Both Pump 132 and control valve 134 are controlled by controller 12. Ammonia sensor 140 is shown coupled to exhaust manifold 48 downstream of catalyst 97. Temperature sensor 142 coupled to catalyst 97 provides an indication of the temperature (T) of catalyst 97. Alternatively, catalyst temperature (T) can be estimated as described later herein with particular reference to FIG. 6. Similarly, particulate filter temperature (Tp) can be read from sensor 143 or estimated using methods known to those skilled in the art based on exhaust gas temperature.