Electrolysis: processes – compositions used therein – and methods – Electrolytic analysis or testing – For nitrogen or nitrogen containing compound
Reexamination Certificate
2000-12-18
2003-03-18
Warden, Sr., Robert J. (Department: 1744)
Electrolysis: processes, compositions used therein, and methods
Electrolytic analysis or testing
For nitrogen or nitrogen containing compound
C205S784500, C205S785000, C204S408000, C204S425000, C204S426000
Reexamination Certificate
active
06533921
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates to an apparatus and method for detecting the concentration of nitrogen oxide as harmful components discharged from a variety of combustion devices, such as internal combustion engines.
BACKGROUND OF THE INVENTION
Following discussions are given on the related art in the light of the present invention.
Up to now, there has been known an apparatus for detecting the concentration of nitrogen oxide in which, as disclosed for example in European Patent Publication 0678740A1, SAE paper No. 960334 p.137 to 142, 1996, a first measurement chamber communicating via a first diffusion rate defining layer with a gas to be measured and a second measurement chamber communicating via second diffusion rate defining layer with this first measurement chamber are formed by an oxygen ion conducting electrolyte layer, a first oxygen pumping cell and an oxygen concentration measurement cell are formed in the first measurement chamber by sandwiching a solid electrolyte layer between porous electrodes and, and in which a second oxygen pumping cell and an oxygen concentration measurement cell are formed in the second measurement chamber by sandwiching a solid electrolyte layer between porous electrodes, to constitute a sensor for detecting the concentration of nitrogen oxides (NOx) in the exhaust gases of the internal combustion engines.
In this type of the nitrogen oxide concentration detecting apparatus, the current is supplied to the first oxygen pumping cell so that the output voltage from the oxygen concentration measurement cell will be at a pre-set constant value and oxygen is pumped out from the first measurement chamber to control the oxygen concentration to a constant value. A constant voltage is applied across the second oxygen pumping cell for further pumping oxygen out of the second measurement chamber. The NOx concentration in the gas under measurement is detected from the value of the current flowing in this second measurement chamber.
In the exhaust gases from the internal combustion engines, that is gases under measurement, there are gaseous components other the NOx, namely oxygen, carbon monoxide or carbon dioxide etc. In the above-mentioned the nitrogen oxide concentration detecting apparatus, the current is caused to flow in the first oxygen pumping cell for extracting oxygen in the first measurement chamber, substantially in its entirety, and a constant voltage is applied across the second oxygen pumping cell in the second measurement chamber in a direction of pumping out oxygen out of the second measurement chamber, to decompose NOx in the gas under measurement into nitrogen and oxygen by the catalytic action of the porous electrode constituting the second oxygen pumping cell, to extract oxygen from the second measurement chamber. This enables detection of the NOx concentration in the gas under measurement without being affected by the gaseous components contained in the gas under measurement.
Also, in this type of the nitrogen oxide concentration detecting apparatus, it is necessary to heat the sensor to a pre-set activation temperature, e.g., not less than 800° C., for correctly measuring the NOx concentration by the above-described detection method. Thus, a heater is separately provided for heating the sensor.
For controlling the sensor to a pre-set temperature using the heater, it may be contemplated to use a control method customarily used in an oxygen sensor configured for detecting the oxygen concentration in the exhaust gases using an oxygen concentration sensor comprised of a solid electrolyte layer sandwiched between porous electrodes.
That is, for controlling the sensor temperature, a variety of methods have been devised, such as a method controlling the amount of the current supplied to the heater so that the heat evolution in the heater will be constant, a method controlling the amount of the heater current by a pre-set control pattern so that the sensor temperature will be a target temperature, or a method of detecting the sensor temperature for controlling the amount of the current supplied to the heater, as disclosed in JP Patent Kokai JP-A-59-163556 or in JP Patent Kokai JP-A-59-214756. It may be envisaged to use these conventional control methods in the nitrogen oxide concentration detecting apparatus.
SUMMARY OF THE DISCLOSURE
However, in the course of the investigation toward the present invention, certain problems have been encountered. That is in distinction from an oxygen sensor, the nitrogen oxide concentration detecting apparatus includes three cells in the sensor. Moreover, since it is difficult to provide a heater in each cell to control its temperature, there is posed a problem of how to apply the above-mentioned control methods.
In the nitrogen oxide concentration detecting apparatus, in particular, if the sensor temperature is changed, the oxygen concentration in the first measurement chamber, controlled by the current allowed to flow in the first oxygen pumping cell, and hence the oxygen concentration in the second measurement chamber, are varied, thus significantly varying the results of detection of the NOx concentration. Thus, for assuring detection accuracy of the NOx concentration, it is demanded that temperature control can be executed efficiently by a simplified structure so that the oxygen concentration in the first measurement chamber is not varied by changes in the sensor temperature. Up to now, a temperature controlling method capable of sufficiently meeting to this request has not been established, such that a nitrogen oxide concentration detection device which has realized temperature characteristics by a simplified structure has not been put to practical use.
Also, the nitrogen oxide concentration detection device suffers from a defect that, since the detected results are varied significantly by changes in the sensor temperature, the results of detection can be affected by changes in temperature of the gas being measured, such that, if the sensor temperature can be controlled accurately, the results of detection tend to be momentarily fluctuated during the transient period when the temperature of the gas being measured is changed.
In view of the above problems, it is a primary object of the present invention to provide a novel nitrogen oxide concentration detection apparatus (or method) capable of efficiently controlling the sensor temperature such as to prevent the results of detection of the NOx concentration from being varied.
It is a second object of the present invention to provide a novel nitrogen oxide concentration detection apparatus (or method) for correcting NOx concentration detection errors accompanying temperature changes of the gas under measurement that cannot be controlled by this temperature control.
Further objects of the present invention will become apparent in the entire disclosure.
According to a first aspect of the present invention, there is provided a nitrogen oxide concentration detection apparatus generally including a main body portion of a sensor having a first measurement chamber and a second measurement chamber. The first measurement chamber has a first oxygen pumping cell and an oxygen concentration measurement cell, the first oxygen pumping cell being made up of an oxygen ion conducting solid electrolyte layer sandwiched between porous electrodes. The first measurement chamber communicates via a first diffusion rate defining layer with a gas under measurement. The second measurement chamber is made up of an oxygen ion conducting solid electrolyte layer sandwiched between porous electrodes, and communicates with the first measurement chamber via a second diffusion rate defining layer. The nitrogen oxide concentration detection apparatus also includes pump current controlling means for pumping out oxygen from the first measurement chamber by the first oxygen pumping cell so that an output voltage of the oxygen concentration measurement cell will be constant, for thereby controlling the oxygen concentration in the first measurement chamber to a const
Inagaki Hiroshi
Kondo Noriaki
Miyata Shigeru
Morrison & Foerster / LLP
NGK Spark Plug Co. Ltd.
Olsen Kaj K.
Warden, Sr. Robert J.
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