The present invention relates to an oxygen sensor for detecting the existence of oxygen in a mixture of gases, and, more particularly, relates to an oxygen sensor for detecting the existence of oxygen in the exhaust gases of an internal combustion engine.
Many internal combustion engines at the present time are fitted with 02 sensors for detecting the remainder of oxygen in the exhaust gases emitted by the engine. The signal from such a sensor is used, typically, for controlling the air/fuel ratio of the combustion in the internal combustion engine, or for controlling purification of the exhaust gases of the internal combustion engine by a catalytic converter.
There is a well known form of construction for such a sensor, comprising an electrolytic tubular body made of solid electrolyte such as zirconia, which is formed as a tube open at its one end and closed at its other end, with an internal electrode coated on the interior surface of the electrolytic tubular body, and an external electrode coated on the exterior surface of the electrolytic tubular body. The electrolytic tubular body is protruded into the exhaust passage of the internal combustion engine, so that the external electrode is exposed to the exhaust gases, and atmospheric air is arranged to be provided to the internal electrode. Thereby, a voltage is generated between the external electrode and the internal electrode, which varies according to the proportion of oxygen present in the exhaust gases.
In such an oxygen sensor it is of the greatest importance for attaining accuracy of the output electrical signal produced thereby that a clean and fresh supply of atmospheric air should be provided to the internal space of the electrolytic tubular body, and to the internal electrode. However, it is important also that contaminants such as moisture, oil, dust, dirt, or the like should not be allowed to penetrate to this internal space, since even a small amount thereof may adversely affect the accuracy of the electrical output signal of the sensor. Further, it is very important that splashed-up water, which typically may be scattered over the exhaust system of the automobile when the automobile passes through a puddle or the like, should not penetrate to the interior of the sensor. However heretofore no ideal construction has yet been found for such an oxygen sensor.