Power plants – Internal combustion engine with treatment or handling of... – Methods
Reexamination Certificate
1999-03-18
2002-12-24
Denion, Thomas (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
Methods
C060S276000, C060S285000, C060S301000
Reexamination Certificate
active
06497092
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to automotive exhaust systems and, in particular, to diagnostic techniques for determining the NO
x
storage capacity of a NO
x
adsorber used in such exhaust systems. This invention also relates to techniques for operating an internal combustion engine in accordance with the storage capacity of a NO
x
adsorber connected in the exhaust system so as to maximize performance of the engine while minimizing the NO
x
exhausted into the environment.
BACKGROUND OF THE INVENTION
Exhaust gas treatment devices have been used as original equipment by automotive manufacturers for many years as a way to reduce the HC, CO, and NO
x
emissions from automotive internal combustion engines. Initially, thermal afterburning was used to reduce emissions by burning the unburnt fuel contained in the exhaust gas. However, this approach has been found to only provide limited benefits and is not useful in reducing NO
x
emissions to acceptable levels. This technique has primarily been replaced by catalytic converters which utilize a monolithic structure containing noble metals (Pt, Rh, Pd) to provide catalytic afterburning of the engine emissions. Today's more advanced systems utilize a three-way catalytic converter that is capable of simultaneously reducing the emissions of HC, CO, and NO
x
. To maximize the efficiency of these three-way converters, the engines are typically run at stoichiometry; that is, they are run at an air/fuel ratio in which the amount of air (oxygen) inducted into the cylinder is no more and no less than required to burn all of the injected fuel. One problem with this mode of engine operation is that it is not always possible or desirable to operate the engine at stoichiometry. Rather, for purposes of maximizing fuel economy, it is often desirable to operate the engine in a lean combustion condition in which the amount of intake air is greater than is needed to burn the injected fuel. Conversely, during engine warm up and during periods of acceleration when torque is required, it is desirable for driveability to operate the engine in a rich combustion condition in which the amount of fuel injected is greater than the amount of fuel that the inducted air can burn.
More recently, NO
x
adsorbers have been developed which store NO
x
during periods of lean engine combustion (i.e., excess air) and then periodically release the NO
x
during periods of rich combustion (i.e., excess fuel) so that the NO
x
can be catalytically reduced due to the presence of excess HC, CO, and H
2
. See, for example, U.S. Pat. No. 5,473,887 to Takeshima et al. which discloses an exhaust purification system that operates to reduce NO
x
emissions by periodically running the engine at a rich combustion condition to release and catalytically reduce the NO
x
stored during the periods of normal lean engine operation. Since the initial development of NO
x
adsorbers, many refinements have been developed to help further regulate and reduce the NO
x
emissions from the exhaust system. For example, U.S. Pat. No. 5,483,795 to Katoh et al. discloses a system in which an exhaust gas oxygen sensor (referred to herein as an O
2
sensor) is placed downstream of the NO
x
adsorber to determine the length of time needed to release all of the stored NO
x
during rich engine operation. The Katoh et al. system works on the principle that after the engine is switched from lean to rich combustion, there is a delay before the downstream O
2
sensor detects a rich combustion condition, with this delay being due to the release of NO
x
which reacts with the HC, CO, H
2
contained in the exhaust. Thus, switching of the downstream O
2
sensor to a voltage indicative of a rich condition is used as a signal that all of the NO
x
stored in the NO
x
adsorber has been released and that the engine can therefore be returned to lean operation.
The amount of NO
x
that can be stored in a NO
x
adsorber during any one lean cycle is dependent upon the state, volume, and temperature of the NO
x
adsorber. Over time, NO
x
adsorbers can deteriorate due to, for example, poisoning from sulfur oxides. Accordingly, exhaust purification systems have been suggested which determine the degree of deterioration and respond accordingly. For example, U.S. Pat. No. 5,577,382 to Kihara et al. discloses a system in which the peak magnitude of a downstream O
2
sensor is used to determine when the NO
x
adsorber has sufficiently deteriorated that it needs to be regenerated by running the engine rich until the stored sulfur oxides are released. Similarly, U.S. Pat. No. 5,735,119 to Asanuma et al. discloses a system which detects the degree of deterioration of the NO
x
adsorber, again using an O
2
sensor. As the degree of deterioration increases, the system decreases the length of engine operating time at both the lean and rich combustion conditions. This has the effect of reducing the amount of NO
x
supplied to the NO
x
adsorber (i.e., the amount of engine-out NOR) before the rich regeneration of the NO
x
adsorber, and also has the effect of reducing the length of the rich regeneration, since there will be less NO
x
adsorbed and hence, less regeneration time required.
Another approach for achieving efficient use of a NO
x
adsorber is to determine the amount of engine-out NO
x
as the engine is operated in its lean combustion mode and to then switch to rich combustion when the total engine-out NO
x
supplied during the current lean period equals the adsorption capacity of the NO
x
adsorber. See, for example, U.S. Pat. No. 5,437,153 to Takeshima et al. Engine-out NO
x
can also be used along with other variables to determine the state of the NO
x
adsorber. See, for example, U.S. Pat. No. 5,743,084 to Hepburn which discloses a method for monitoring a NO
x
trap in which upstream and downstream O
2
sensors are used to determine the amount of NO
x
stored in the NO
x
trap, with the stored NO
x
amount being used along with an estimated engine-out NO
x
to determine the storage efficiency of the NO
x
trap. Thereafter, the period of lean engine operation is reduced as the determined storage efficiency drops. This system is based upon the same essential principle as that disclosed in the above-noted Katoh et al. patent; namely, that the delay in switching of the downstream O
2
sensor when engine operation changes from lean to rich is due to the release of NO
x
stored in the NO
x
trap, and for a given temperature, this delay time provides a quantitative measure of the amount of NO
x
released (and therefore previously stored) in the NO
x
trap.
One problem with using the O
2
sensor delay time as a measure of the amount of stored NO
x
is that the delay time is not only due to the release of stored NO
x
, but also to the release of oxygen stored during the lean period. Thus, in U.S. Pat. No. 5,713,199 to Takeshima et al., the amount of delay time due to the release of oxygen is determined and is subtracted from the total O
2
sensor delay to determine the amount of delay due to the release of NO
x
only. This truer delay time can then be used to more accurately estimate the amount of NO
x
stored during the previous lean period. The amount of delay time due to the release of oxygen is determined by a separate lean/rich cycle in which the engine must be operated lean for a period of time that is long enough to fully store the oxygen in the NO
x
adsorber, but is short enough that no appreciable NO
x
has yet been stored. The engine is then switched to rich operation, and the delay time between the upstream and downstream O
2
sensors is taken as a measure of the delay due to the release of oxygen only in the NO
x
adsorber. This delay is later subtracted from the total delay when the engine is operated in its normal lean/rich cycle. While providing a more accurate measurement of the delay due to the release of NO
x
only (and, thus a more accurate measurement of the amount of stored NO
x
), this system requires a separate abnormal lean/rich engine cycle to determine the oxygen release delay time
Cichosz Vincent A.
Delphi Technologies Inc.
Denion Thomas
Trieu Thai-Ba
LandOfFree
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