Power plants – Internal combustion engine with treatment or handling of... – Methods
Reexamination Certificate
1999-11-10
2001-10-16
Denion, Thomas (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
Methods
C060S275000, C060S276000, C060S277000, C204S425000
Reexamination Certificate
active
06301878
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus for cleaning the exhaust gas of an internal combustion engine, and more specifically to a method and apparatus which uses an NOx pickup to determine the amount of oxygen present in an exhaust gas by measuring the decomposition of NH
3
in the NOx pickup.
It is known to use a three-way catalyst in the exhaust gas tract of an internal combustion engine to clean the exhaust gas. It is also known to use provide a lambda probe whose output signal is dependent upon the residual oxygen content in the raw exhaust upstream from the catalyst. It is believed that the residual oxygen content in the raw exhaust depends upon the fuel/air mixture dispersed in the internal combustion engine. It is known that in case of excess fuel (rich mixture), the residual oxygen content in the raw exhaust is lower, and in case of excess air (lean mixture), the residual oxygen content in the raw exhaust is higher.
It is known that in a lean mixture (lambda>1), an output voltage of the lambda probe is usually less than about 100 mV. It is also known that the output voltage of the lambda probe changes almost abruptly near lambda=1, and the output voltage of the lambda probe increase to about 0.8 volt in rich mixture (lambda<1). This is referred to as a two-point action.
There are also known broad-band lambda probes that are capable of outputting signals corresponding to a lambda range (0.7 to 4) in a linear fashion.
It is known to operate an internal combustion engine such that the signal output by the lambda probe, indicating the residual oxygen level in the raw exhaust, varies around a predetermined average which corresponds to a value for lambda=1, for example. It is believed that a three-way catalyst has a certain lambda value &lgr;o with optimal catalytic properties. Thus, the predetermined average of lambda values during the operation of the internal combustion engine should actually be substantially &lgr;o. It is also known, however, to vary the lambda value &lgr;o for optimum catalytic properties from lambda=1, for example lambda=0.99.
It is believed that static and dynamic properties of the lambda probe upstream from the three-way catalyst are altered by aging and poisoning. It is believed that this causes a position of a signal level corresponding to &lgr;o to change. It is known to use an additional lambda probe downstream from the three-way catalyst, which is believed to be less sensitive to poisoning. It is believed that the additional lambda probe may serve as a monitor probe to measure and confirm the catalytic conversion and permit fine regulation of the fuel/air mixture by correcting the signal level corresponding to &lgr;o in the lambda probe upstream, such that the lambda value &lgr;o most favorable to catalytic conversion is maintained. This process is called “guiding control” or “trimming.”
It is believed that in order further to reduce pollutant emissions from internal combustion engines, an NOx catalyst can be provided in addition to the three-way catalyst. It is known that the NOx catalyst can also be integrated into the three-way catalyst. It is also known to use a storage catalyst that includes one state of operation which stores NOx and another state of operation which converts the stored NOx. It is known to use a measuring pickup sensitive to NOx downstream from the NOx catalyst to achieve the optimum operation of an NOx catalyst.
The present invention addresses the problem of substantially effectively reducing a residual oxygen content of an exhaust gas of an internal combustion engine without the use of an additional lambda probe downstream of a catalytic converter.
SUMMARY OF THE INVENTION
The present invention provides a method for cleaning the exhaust gas of an internal combustion engine with a catalyst having three-way properties disposed in the exhaust tract and a lambda probe disposed upstream from the catalyst, in which the control of the operation of the internal combustion engine is performed such that the lambda value of the raw exhaust gas assumes predetermined values at the lambda probe, while a certain signal level of the lambda probe is associated with a lambda value &lgr;o which is close to lambda=1, the concentration of an exhaust gas component downstream from the catalyst showing three-way properties is measured by means of an additional measuring pickup, and the signal level associated with the &lgr;o is corrected accordingly, characterized in that an NOx measuring pickup is used as an additional measuring pickup which detects the NOx concentration in the exhaust gas, a relationship between NOx concentration in the exhaust gas and the lambda value of the exhaust gas is given such that for lambda values>1 the NOx concentration increases greatly and with it the output signal of the measuring pickup, which shows a cross-sensitivity to NH
3
, so that for lambda values <1 the output signal of the measuring pickup likewise increases, and which has an internal signal which at lambda=1 has a sign change, and a correction of the signal level associated with &lgr;o is performed using the relationship between the NOx concentration in the exhaust gas and the lambda value of the exhaust gas by means of the output signal and the internal signal of the measuring pickup.
The present invention also provides an apparatus for cleaning the exhaust gas of an internal combustion engine having a catalyst disposed in the exhaust tract and having three-way properties, a lambda probe disposed upstream from the catalyst, an operation control apparatus which controls the operation of the internal combustion engine such that the exhaust gas at the lambda probe assumes predetermined lambda values, while a certain signal level of the lambda probe is associated with a lambda value &lgr;o which is close to lambda=1, and an additional measuring pickup disposed downstream of the catalyst, which detects the concentration of an exhaust gas component, characterized in that the additional measuring pickup is an NOx measuring pickup which detects the NOx concentration in the exhaust gas, a relationship between NOx concentration in the exhaust gas and the lambda value of the exhaust gas is given such that, for lambda values>1 the NOx concentration in the exhaust gas and thus the output signal of the measuring pickup increases greatly, which shows a cross-sensitivity to NH
3
so that for lambda values<1 the output signal of the measuring pickup likewise increases, which has an internal signal (Ip
0
) which has a sign change at lambda=1, and which is so connected with the operation control apparatus such that the output signal and the internal signal (Ip
0
) are fed to it so that the operation control apparatus, utilizing the relationship between the NOx concentration in the exhaust gas and the lambda value of the exhaust gas, performs a correction of the signal level associated with &lgr;o by means of the output signal and of the internal signal (Ip
0
) of the measuring pickup.
According to the present invention, a measuring pickup is provided downstream from the catalyst having three-way properties, and it detects the NOx concentration in the exhaust gas. Between the NOx concentration and the lambda value there is a relationship which is utilized for correcting the signal level, associated with &lgr;o, of the probe situated upstream from the catalyst.
The invention sets out from the knowledge that the signal of the measurement pickup has only a local minimum near the &lgr;o-associated value at the NOx concentration corresponding to lambda=1, if the measuring pickup detecting the NOx concentration shows a cross sensitivity to NH
3
. This is the case, for example, with known oxygen ion-conducting solid electrolyte measuring pickups which have a measuring cell in which an oxygen concentration corresponding to lambda=1 is established. Thus, such a measurement of the association does not permit a clear association of an NOx concentratio
Pfleger Corinna
Roessler Juergen
Zhang Hong
Denion Thomas
Siemens Aktiengesellschaft
Tran Binh
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