Chemistry: electrical and wave energy – Apparatus – Electrolytic
Reexamination Certificate
1998-06-19
2001-12-25
Warden, Sr., Robert J. (Department: 1744)
Chemistry: electrical and wave energy
Apparatus
Electrolytic
C204S426000, C205S781000
Reexamination Certificate
active
06332965
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a gas concentration measuring method and a related composite gas sensor preferably used in an exhaust gas purification system employed in an internal combustion engine of an automotive vehicle.
Exhaust gases emitted from the internal combustion engines are main causes of the present-days serious air pollution. To suppress any harmful substances involved in the exhaust gas, the related laws and regulations have been becoming severe year by year.
In view of the foregoing, the air-fuel ratio of the gas mixture supplied to a combustion chamber of the internal combustion engine must be precisely controlled. Similarly, the ignition timing of the internal combustion engine must be carefully controlled. Furthermore, many of the internal combustion engines are equipped with catalytic converters to purify the exhaust gas.
According to the OBD-II regulation in the United States, each purification system is required to have the capability of judging whether or not the catalytic converter operates properly. To this end, an advanced exhaust gas purification system proposes to directly measure the harmful substances, i.e., NOx concentration, as well as precisely controlling the engine combustion.
In general, the catalytic converter is disposed in an exhaust gas passage of an internal combustion engine. When the catalytic converter deteriorates, an increased amount of NOx gas flows across the catalytic converter. In other words, the deterioration of the catalytic converter can be known by the increase amount of the NOx gas not trapped by the catalytic converter. Accordingly, an appropriate NOx sensor is provided downstream of the catalytic converter to detect the change of NOx concentration.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a gas concentration measuring method for simultaneously measuring both the NOx concentration and the air-fuel ratio of a sample gas.
Another object of the present invention is to provide a gas concentration measuring method for simultaneously measuring all of the NOx concentration, the air-fuel ratio and the oxygen concentration of the sample gas.
Another object of the present invention is to provide a gas concentration measuring method for measuring a sample gas temperature as well as the NOx gas concentration and the air-fuel ratio of the sample gas.
Another object of the present invention is to provide a composite gas sensor preferably used in these measuring methods.
In order to accomplish this and other related objects, various aspects of the present invention provides gas concentration measuring methods and related composite gas sensors.
According to a first aspect of the present invention, the composite gas sensor comprises:
oxygen ion conductive solid electrolytic substrates defining at least part of a reference gas chamber and a sample gas chamber;
a sample gas introducing passage introducing a sample gas to the sample gas chamber;
a pump cell having a pair of pumping electrodes for adjusting an oxygen gas amount introduced or exhausted into or from the sample gas chamber, one of the pumping electrodes facing the sample gas chamber and the other of the pumping electrodes facing an outside of the composite gas sensor;
a first sensor cell having a pair of NOx sensing electrodes for detecting a NOx concentration in the sample gas chamber, one of the NOx sensing electrodes facing the sample gas chamber and the other of the NOx sensing electrodes facing the reference gas chamber;
a second sensor cell having a pair of oxygen sensing electrodes for detecting an oxygen concentration in the sample gas chamber, one of the oxygen sensing electrodes facing the sample gas chamber and the other of the oxygen sensing electrodes facing the reference gas chamber;
a first detecting circuit including a first ammeter and an electric power source connected to the first sensor cell for measuring a sensing current of the first sensor cell;
a pump circuit including a second ammeter and a variable electric power source connected to the pump cell for measuring a current of the pump cell; and
a second detecting circuit including a first voltmeter connected to the second sensor cell for measuring a sensing voltage of the second sensor cell.
Using the above-described composite gas sensor, the gas concentration measuring method in accordance with the first aspect of the present invention comprises the steps of:
controlling the variable electric power source of the pump circuit to produce a constant value from the first voltmeter;
measuring the NOx concentration of the sample gas based on a measurement by the first ammeter; and
measuring an air-fuel ratio of the sample gas based on a measurement by the second ammeter.
Furthermore, the gas concentration measuring method in accordance with the first aspect of the present invention comprises the step of measuring an oxygen concentration of the sample gas based on a measurement by a second voltmeter connected between the other pumping electrode facing the outside of the composite gas sensor and the other oxygen sensing electrode facing the reference gas chamber.
According to the first aspect of the present invention, it is preferably that the sample gas chamber includes a first chamber and a second chamber communicating with each other via a diffusive passage. The sample gas introducing passage is directly connected to the first chamber. The one of the pumping electrodes faces the first chamber. The one of the NOx sensing electrodes faces the second chamber. And, the one of the oxygen sensing electrodes faces the second chamber.
Furthermore, the composite gas sensor may comprise a third detecting circuit including a second voltmeter connected between an external electrode facing the outside of the composite gas sensor and the other oxygen sensing electrode facing the reference gas chamber, and an oxygen concentration detector associated with the third detecting circuit for measuring an oxygen concentration of the sample gas based on a measurement by the second voltmeter.
It is further preferable that the sample gas chamber and the reference gas chamber are provided at a same surface level.
It is further preferable that the other NOx sensing electrode and the other oxygen sensing electrode are a common electrode facing the reference gas chamber.
It is further preferable that the sample gas introducing passage is a pinhole. Alternatively, the sample gas introduction passage may be formed by a porous layer having a porosity larger than that of the solid electrolytic substrates.
According to a second aspect of the present invention, the composite gas sensor comprising:
oxygen ion conductive solid electrolytic substrates defining at least part of a reference gas chamber and a sample gas chamber;
a sample gas introducing passage introducing a sample gas to the sample gas chamber;
a pump cell having a pair of pumping electrodes for adjusting an oxygen gas amount introduced or exhausted into or from the sample gas chamber, one of the pumping electrodes facing the sample gas chamber and the other of the pumping electrodes facing an outside of the composite gas sensor;
a first sensor cell having a pair of NOx sensing electrodes for detecting a NOx concentration in the sample gas chamber, one of the NOx sensing electrodes facing the sample gas chamber and the other of the NOx sensing electrodes facing the reference gas chamber;
a second sensor cell having a pair of oxygen sensing electrodes for detecting an oxygen concentration in the sample gas chamber, one of the oxygen sensing electrodes facing the sample gas chamber and the other of the oxygen sensing electrodes facing the reference gas chamber;
a first detecting circuit including a first ammeter and an electric power source connected to the first sensor cell for measuring a sensing current of the first sensor cell;
a pump circuit including a second ammeter and a variable electric power source connected to the pump cell for measuring a current of the pump cell;
a second detecting circuit including a firs
Miwa Naoto
Sano Hiromi
Shibata Masahiro
Shibata Raina
Sugiyama Tomio
Denso Corporation
Olsen Kaj K.
Pillsbury & Winthrop LLP
Shibata Raina
Warden, Sr. Robert J.
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