Measuring and testing – Gas analysis – Gas of combustion
Reexamination Certificate
1999-10-12
2001-11-13
Fuller, Benjamin R. (Department: 2855)
Measuring and testing
Gas analysis
Gas of combustion
Reexamination Certificate
active
06314790
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an oxygen concentration detecting apparatus having a limit current type oxygen sensor comprising an oxygen concentration detecting element that outputs limit current proportional to oxygen concentration and a heater for heating the detecting element and, more particularly, to an oxygen concentration detecting apparatus that checks for abnormality of the limit current type oxygen sensor.
2. Description of Related Art
Many modern air-fuel ratio control systems use limit current type oxygen sensors (oxygen concentration detectors). In such a system, the oxygen concentration detected by the air-fuel ratio sensor is inputted to a microcomputer to calculate an air-fuel ratio, and the microcomputer performs air-fuel ratio feedback control based on the calculated air-fuel ratio. The control system thereby achieves optimal combustion in the internal combustion engine and reduces harmful substances in exhaust gas, such as CO, HC, NOx and the like.
However, since the control precision of the air-fuel ratio control systems is heavily degraded if the reliability of detection of the air-fuel ratio deteriorates, there has been a strong demand for a technology that precisely detects an abnormality of an air-fuel ratio sensor. For example, Japanese Unexanmined Patent Application Publication No. Hei. 1-232143, “Air-Fuel Ratio control Apparatus for Internal Combustion Engine”, describes a technology that detects an abnormality of a heater if the temperature of the air-fuel ratio sensor (oxygen concentration detecting element) detected by a temperature sensor fails to rise to a predetermined temperature. Japanese Unexamined Patent Application Publication No. Hei. 3-189350, “Oxygen Sensor Heater Control Apparatus”, describes a technology for use in an apparatus for controlling the power supply to the heater so that the heater resistance becomes equal to a target resistance, the technology detecting an abnormality of the target resistance if the power supply to the heater deviates from a predetermined range.
However, the conventional art has the following problems. The aforementioned former technology (Japanese Unexamined Patent Application Publication No. Hei. 1-232143) requires a sensor for detecting the temperature of the air-fuel ratio sensor, and thus has problems of high costs. The latter technology (Japanese Unexamined Patent Application Publication No. Hei. 3-189350) merely determines whether the target resistance is properly set, and the occasions when this diagnosis technology detects abnormality are substantially limited to the occasions when the battery or the sensor has been replaced. Thus, this technology does not make a determination regarding the reliability of the oxygen sensor.
SUMMARY OF THE INVENTION
In view of the problems of the conventional art, an object of the present invention is to propose a novel diagnosis technology and thereby provide an oxygen concentration detecting apparatus that precisely and easily checks for abnormality of a limit current type oxygen sensor.
This object is achieved according to a first aspect of the present invention by providing an oxygen concentration detecting apparatus which determines whether the oxygen sensor is abnormal on the basis of whether the element temperature of the oxygen sensor is within a predetermined range. Thereby, this apparatus precisely and easily performs the sensor diagnosis.
Preferably, the oxygen concentration detecting apparatus performs the sensor diagnosis to distinguish a low element temperature abnormality and a high element temperature abnormality.
It is also possible that the oxygen concentration detecting apparatus determines whether the oxygen sensor is abnormal on the basis of whether the output from the oxygen sensor has changed within a predetermined range in response to an increase or a decrease of the fuel supply. Thus, this construction precisely and easily performs the sensor diagnosis.
Moreover, it is possible that the oxygen concentration detecting apparatus performs the sensor diagnosis when the oxygen sensor is or must be activated, thus achieving accurate diagnosis.
Further, the system may feedback-control the heater power supply to make the element temperature of the oxygen sensor substantially equal to a target element temperature and perform the diagnosis of the oxygen sensor on the basis of whether the heater power supply is greater than a predetermined abnormality determination criterion. Thus, this system precisely and easily performs the sensor diagnosis.
Also, the apparatus may achieve optimal diagnosis in accordance with the operating conditions of the engine.
The apparatus may perform the diagnosis of the oxygen sensor on the basis of whether the accumulation of the heater power supply is greater than a predetermined abnormality determination criterion. Thus, this apparatus enhances the precision of diagnosis data and achieves accurate diagnosis.
Moreover, the apparatus may allow the sensor diagnosis to be executed only if the initial heater resistance is equal to or less than a predetermined value that indicates the cold state of the oxygen sensor. Thus, the apparatus inhibits the sensor diagnosis, for example, when the engine is restarted after warming up and the accumulation of the heater power supply is relatively small, thereby maintaining the high precision of the sensor diagnosis.
Other objects and features of the invention will appear in the course of the description thereof, which follows.
REFERENCES:
patent: 4732128 (1988-03-01), Yoshioka et al.
patent: 5090387 (1992-02-01), Mayer et al.
patent: 5148795 (1992-09-01), Nagai et al.
patent: 5214267 (1993-05-01), Hoshi et al.
patent: 5513522 (1996-05-01), Seki et al.
patent: 5629473 (1997-05-01), Hayami
patent: 5719778 (1998-02-01), Suzumura et al.
patent: 6009866 (2000-01-01), Sagisaka et al.
patent: 1-232143 (1989-09-01), None
patent: 3-189350 (1991-08-01), None
patent: 4-69565 (1992-03-01), None
Sagisaka Yasuo
Yamashita Yukihiro
Davis Octavia
Fuller Benjamin R.
Nippondenso Co. Ltd.
Pillsbury & Winthrop LLP
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