Chemistry: electrical and wave energy – Apparatus – Electrolytic
Reexamination Certificate
2001-10-30
2003-12-02
Olsen, Kaj K. (Department: 1753)
Chemistry: electrical and wave energy
Apparatus
Electrolytic
C204S401000, C204S426000, C204S427000, C205S781000, C073S023310
Reexamination Certificate
active
06656337
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates generally to a gas concentration sensor for measuring the concentration of gases which may be employed in an air-fuel ratio control system for automotive vehicles, and more particularly to a limiting current type gas concentration measuring apparatus equipped with a limiting current type gas sensor which is designed to compensate for an error in determining the concentration of a gas.
2. Background Art
Limiting current type gas concentration sensors are known which are used for measuring NOx contained in exhaust gasses of automotive engine. There is used one of such gas concentration sensors which includes a pump cell and a sensor cell. The pump cell works to pump oxygen (O
2
) contained in gasses admitted into a gas chamber out of the sensor or to pump oxygen (O
2
) of outside gasses into the gas chamber. The sensor cell works to measure the concentration of NOx contained in the gasses after passing through the pump cell. The pump cell and the sensor cell are designed to produce current signals indicative of the concentration of oxygen and NOx upon application of voltage thereto.
Another type of gas concentration sensor is known which includes a monitor cell in addition to the pump cell and the sensor cell. The monitor cell works to produce an electromotive force as a function of the concentration of oxygen within the gas chamber. A control system is also proposed which controls the voltage to be applied to the pump cell of such a three-cell gas concentration sensor under PID feedback (e.g., Academic Lecture Preliminary Report, Automotive Technical Meeting Corporation and SAE 970858). Specifically, this system is designed to determine the voltage to be applied to the pump cell based on a difference between an actual electromotive force produced by the monitor cell and a target one predetermined for keeping the concentration of oxygen at a lower level within the gas chamber.
The measurement of the concentration of exhaust gasses in the three-cell gas concentration sensor is achieved by introducing the exhaust gasses from the pump cell toward the monitor cell. Thus, when the concentration of exhaust gasses varies, a difference in concentration of the exhaust gasses between the pump cell and the monitor cell is resulted from a lag caused by the time required for the exhaust gasses to flow from the pump cell to the monitor cell. The time will, therefore, be consumed until the concentration of the exhaust gasses at the monitor cell agrees with that at the pump cell. This problem will be objectionable in a gas concentration sensor in which an orifice is provided between the pump cell and the monitor cell. Accordingly, when the voltage to be applied to the pump cell is feedback controlled as a function of the electromotive force produced by the monitor cell, a shift in feedback control phase may result in oscillation.
For instance, when it is required to change the exhaust gasses to a lean side, so that a large quantity of oxygen flows into the gas chamber, it is difficult for the monitor cell to detect such changing, thereby resulting in insufficient quantity of oxygen pumped by the pump cell under the feedback control using an output of the monitor cell. A large quantity of oxygen, thus, remains undesirably within the gas chamber. Subsequently, when the lean condition of the exhaust gasses is detected based on the output of the monitor cell, it will cause an excess voltage to be applied to the pump cell to pump the residual oxygen out of the gas chamber thereinto, after which the monitor cell continues to provide an output indicative of the lean condition for a while. After it is found that too much oxygen has been pumped out of the gas chamber, the voltage applied to the pump cell is change rapidly to a lower level.
The above phenomenon is repeated, thereby leading to oscillation of a control system applying the voltage to the pump cell, so that a residual quantity of oxygen within the gas chamber changes greatly in a cycle. This may cause the quantity of oxygen contained in the exhaust gasses flowing to the sensor cell to increase or the pump cell to decompose NOx undesirably. When the former is taken place, the sensor cell decomposes the increased quantity of oxygen to increase an offset current contained in an output thereof. When the latter is taken place, it results in insufficient quantity of NOx contained in the exhaust gasses flowing to the sensor cell, thus producing an error in determining the concentration of NOx.
Additionally, when the response rate of each cell is changed with a change in temperature of the exhaust gasses or deterioration of the cell, a residual quantity of oxygen within the gas chamber also changes, thus resulting in a decrease in accuracy of determining the concentration of NOx. For instance, in a case where enriched exhaust gases are admitted into the gas chamber, and a rich gas component (e.g., HC) sticks to an electrode of the monitor cell, the monitor cell continues to produce an output indicative of the rich condition in error even after the exhaust gasses is changed to the lean side. This causes the voltage applied to the pump cell to be controlled so that oxygen (O
2
) of outside gasses may be pumped into the gas chamber. Afterwards, when the rich gas component sticking to the electrode of the monitor cell reacts with the oxygen and peels, the monitor cell produces an output indicative of changing to the lean side, so that the voltage to be applied to the pump cell is so controlled as to pump the oxygen out of the gas chamber. At this time, the concentration of oxygen within the gas chamber is increased extremely, thus resulting in application of an excess voltage to the pump cell. Similarly, in a case where the exhaust gases are switched from lean to rich, and a lean gas component (e.g., O
2
) sticks to the electrode of the monitor cell, the monitor cell continues to produce an output indicative of the lean condition in error even after the exhaust gasses is changed to the rich side. This causes the voltage applied to the pump cell to be controlled so that oxygen (O
2
) may be pumped out of the gas chamber. Specifically, an excess voltage is applied to the pump cell so as to decompose NOx as well as O
2
.
The above event is repeated, thereby leading to oscillation of the control system applying the voltage to the pump cell, so that a residual quantity of oxygen (O
2
) within the gas chamber changes greatly in a cycle. This results in decreased accuracy of determining the concentration of NOx.
SUMMARY OF THE INVENTION
It is therefore a principal object of the present invention to avoid the disadvantages of the prior art.
It is another object of the present invention to provide a gas concentration measuring apparatus designed to eliminate an error in determining the concentration of a specified gas component of measurement gases.
According to one aspect of the invention, there is provided a gas concentration measuring apparatus which may be employed with an automotive control system designed to control the quantity of fuel injected into an internal combustion gasoline engine as a function of an output of the gas concentration measuring apparatus under feedback (F/B) control to bring the air-fuel (A/F) ratio into agreement with a target value. The gas concentration measuring apparatus comprises: (a) a gas concentration sensor including a gas chamber, a first cell responsive to application of a voltage to pump thereinto oxygen molecules contained in gasses admitted into the gas chamber and discharge the pumped oxygen molecules to produce an electric current indicative of a concentration of the oxygen molecules, a second cell working to determine a concentration of a specified oxygen containing gas component contained in the gasses having passed through the first cell, and a monitor cell working to monitor a concentration of residual oxygen molecules within the gas chamber and provide an output indicative thereof; (b) an applying voltage determining ci
Hada Satoshi
Kurokawa Eiichi
Niwa Mitsunobu
Suzuki Toshiyuki
Denso Corporation
Nixon & Vanderhye PC
Olsen Kaj K.
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