Electrolysis: processes – compositions used therein – and methods – Electrolytic analysis or testing – For nitrogen or nitrogen containing compound
Reexamination Certificate
1997-11-06
2001-04-10
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
06214207
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates to a method and apparatus for measuring the oxygen concentration and the nitrogen oxide concentration using an NOx sensor designed for detecting the concentration of nitrogen oxides as toxious components exhausted from a variety of combustion equipments, such as internal combustion engines.
BACKGROUND
There has hitherto been known a nitrogen oxide concentration measurement device for measuring the concentration of nitrogen oxides (NOx) in exhaust gases of, for example, internal combustion engines, using an NOx sensor in which, as disclosed for example in European publication EP 0678740A1, and SAE paper No.960334 pages 137 to 142, 1996, etc., a first measurement chamber communicating with a measured gas side via first diffusion rate-regulating layer and a second measurement chamber communicating with this first measurement chamber via a second diffusion rate regulating layer are formed of oxygen ion conductive solid electrolyte layers, a first oxygen pumping cell and an oxygen concentration measurement cell are formed on the first measurement chamber by each sandwiching a solid electrolyte layer by a pair of porous electrodes, and in which a second oxygen pumping cell is formed on the second measurement chamber similarly by sandwiching a solid electrolyte layer by another pair of porous electrodes.
In this type of the nitrogen oxide concentration measurement device, the current is caused to flow across the first oxygen pumping cell so that an output voltage from the oxygen concentration measurement cell will be a pre-set constant value for applying a pre-set constant voltage across the second oxygen pumping cell while maintaining a constant oxygen concentration in the first measurement chamber for pumping out oxygen from the second measurement chamber by applying a constant voltage across the second oxygen pumping cell. The NOx concentration in the gas under measurement is detected based on the current value flowing in the second oxygen pumping cell.
It is noted that gas components other than NOx, that is oxygen, carbon monoxide or carbon dioxide, are present in the exhaust gases from the internal combustion engines, that is gas under measurement. In the above-described nitrogen oxide concentration measurement device, the inside of the first measurement chamber is controlled by the first oxygen pumping cell to an extremely low oxygen concentration, while a constant voltage is applied across the second oxygen pumping cell in a direction of pumping out oxygen from the second measurement chamber, on the side of the second measurement chamber into which flows the gas controlled to the low oxygen concentration, thereby decomposing NOx in the gas under measurement into oxygen and nitrogen by the catalytic function of the porous electrode constituting the second oxygen pumping cell and extracting oxygen from the second measurement chamber. The pump current flowing at this time through the second oxygen pumping cell is detected in an attempt for measuring the NOx concentration in the gas under measurement without being affected by the other gas components in the gas under measurement.
For accurate detection of the NOx concentration by the above detection method using the above nitrogen oxide concentration measurement device, each cell needs to be activated by heating the sensor to a pre-set activation temperature, such as 800° C. or higher. Thus, a separate heater is provided for heating the sensor.
SUMMARY OF THE DISCLOSURE
In the course of eager investigation toward the present invention the following problems have been encountered.
Meanwhile, the above-described nitrogen oxide concentration measurement device is used, for instance, for monitoring the state of the NOx catalyst which reduces NOx for suppressing NOx in an internal combustion engine driven at a lean air/fuel ratio, that is with an air/fuel ratio having a proportion of air larger than fuel, thus increasing the NOx component in the exhaust gases, i.e., a so-called lean-burn engine.
Namely, the above-described nitrogen oxide concentration measurement device is used for performing such control in which an NOx sensor is loaded downstream of the NOx catalyst in an exhaust path of the internal combustion engine to measure the NOx concentration for detecting the amount of leakage of NOx from the NOx catalyst, and in which, when the amount of leakage of NOx starts to increase, the air/fuel ratio of the air/fuel mixture supplied to the internal combustion engine is transiently controlled to a fuel-rich air/fuel ratio for discharging unburned gas from a internal combustion engine, with the unburned gas being reacted with NOx accumulated in the NOx catalyst for suppressing emission of NOx.
For realizing this NOx control, a separate air/fuel ratio measurement device for measuring the air/fuel ratio based on the oxygen concentration in the exhaust gas needs to be provided in the internal combustion engine, because the above-mentioned nitrogen oxide concentration measurement device cannot measure the air/fuel ratio of the air/fuel mixture supplied to the internal combustion engine.
For realizing the above-described NOx control, the air/fuel mixture control commnonly carried out in the internal combustion engine in the conventional practice needs to be executed simultaneously. To this end, an NOx sensor and an oxygen concentration sensor (so-called air/fuel ratio Sensor) need to be provided in the exhaust gas system of the internal combustion engine.
It is therefore an object of the present invention to provide a method and a device for measuring oxygen concentration and NOx (nitrogen oxide) concentration only by an NOx sensor without using two sensors, namely a NOx sensor and an air/fuel ratio sensor, particularly, for simplifying the Structure of the detection system of the NOx concentration and oxygen concentration (air/fuel ratio) in implementing the above-described NOx control.
Other objects will become apparent from the entire disclosure of the present invention.
According to a first aspect of the present invention there is provided a method for measuring the oxygen concentration and the nitrogen oxide concentration in a gas under measurement using a NOx sensor having a first measurement chamber, a second measurement chamber and a heater. The first measurement chamber has a first oxygen pumping cell and an oxygen concentration measuring cell and communicating with (the side of) the gas under measurement of a first diffusion rate regulating layer. The first oxygen pumping cell has an oxygen ion conductive solid electrolyte layer sandwiched between porous electrodes. The second measurement chamber has a second oxygen pumping cell having an oxygen ion conductive solid electrolyte layer sandwiched between porous electrodes and communicates with the first measurement chamber via a second diffusion rate regulating layer. The heater is adapted for heating the cells to a pre-set activation temperature. The method includes the step of causing the current to flow in the first oxygen pumping cell so that an output voltage of the oxygen concentration measurement cell will be of a pre-set value for controlling the oxygen concentration in the first measurement chamber to a constant value, the step of applying a constant voltage across the second oxygen pumping cell in a direction of pumping out oxygen out of the first measurement chamber, and the step of measuring the concentration of nitrogen oxide in the gas under measurement based on the value of the current flowing in the second oxygen pumping cell and measuring the oxygen concentration in the gas under measurement based on the value of the current flowing in the first oxygen pumping cell.
In a second aspect according to the first aspect, the amount of the current supplied to the heater is controlled so that the temperature of the oxygen concentration measurement cell in the NOx sensor will be a pre-set target temperature.
In a third aspect according to the second aspect, the measured results of the oxygen concentration and the nitro
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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