Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – With indicator or control of power plant
Reexamination Certificate
2000-03-03
2001-10-16
Wolfe, Willis R. (Department: 3747)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
With indicator or control of power plant
C123S697000, C073S023320, C204S406000, C204S425000
Reexamination Certificate
active
06304813
ABSTRACT:
INCORPORATION BY REFERENCE
The disclosure of Japanese Patent Application Nos. HEI 11-86335 filed on Mar. 29, 1999 and HEI 11-220254 filed on Aug. 3, 1999, including the specifications, drawings and abstracts are incorporated herein by reference in their entirety.
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to an oxygen concentration detector and methods of using the oxygen concentration detector.
2. Description of Related Art
According to air-fuel ratio control of engines in recent years, an air-fuel ratio sensor and a catalyst are disposed in the exhaust system of the engine, and feedback control is performed such that an air-fuel ratio of exhaust gas detected by the air-fuel ratio sensor becomes equal to a target air-fuel ratio, for example, a stoichiometric air-fuel ratio, with a view to purifying the maximum possible amounts of noxious substances contained in the exhaust gas (such as HC, CO, NOx and the like) by means of the catalyst. As the air-fuel ratio sensor, a &lgr;-type air-fuel ratio sensor (referred to as the O
2
sensor) is used. The &lgr;-type air-fuel ratio sensor has a Z-characteristic for determining, based on a concentration of oxygen contained in exhaust gas discharged from the engine, whether an air-fuel ratio of exhaust gas in the engine is rich or lean.
Alternatively, as the air-fuel ratio sensor, a limiting current-type oxygen concentration detecting element for outputting a limiting current proportional to the concentration of oxygen contained in exhaust gas discharged from the engine is used. The limiting current oxygen concentration detecting element detects the air-fuel ratio of exhaust gas in the engine from a concentration of oxygen, over a wide range and linearly. The limiting current oxygen concentration detecting element is effective in enhancing precision of the air-fuel ratio control and in performing control such that an air-fuel ratio of exhaust gas in the engine becomes equal to a target air-fuel ratio over a wide range of rich, stoichiometric and lean air-fuel ratios.
In order to maintain precision in detecting an air-fuel ratio, it is indispensable to keep the aforementioned air-fuel ratio sensor, namely, the O
2
sensor or the limiting current type oxygen concentration detecting element, in an activated state. Normally, as soon as the engine is started, a heater attached to the O
2
sensor or to the limiting current type oxygen concentration detecting element is supplied with electric power, whereby the sensor or the detecting element is heated and activated at an early stage. Thus, in order to maintain an activated state of the sensor or the detecting element, heater conduction control is performed.
According to a heater control device of an air-fuel ratio sensor disclosed in Japanese Patent Application Laid-Open No. HEI 8-278279, during an initial conduction period for a heater, all the electric power, that is, electric power with a duty ratio of 100%, is supplied to the heater for early activation of an element of the air-fuel ratio sensor, until the heater reaches a predetermined temperature. If the heater reaches the predetermined temperature, electric power corresponding to the temperature of the heater is supplied to the heater. If the sensor element reaches a predetermined temperature, electric power corresponding to the temperature of the element of the air-fuel ratio sensor is supplied to the heater.
However, in the heater control device of the air-fuel ratio sensor disclosed in Japanese Patent Application Laid-Open No. HEI 8-278279 mentioned above, at the time of the cold starting operation of the engine, water that has condensed in a catalyst provided upstream in an exhaust pipe either accumulates in a bottom portion of the exhaust pipe, or sticks to a wall surface of the exhaust pipe. If the exhaust system has not been warmed up at the time of the cold starting operation of the engine, the condensed water splashes together with exhaust gas and passes through small holes in a protector cover attached to the exhaust pipe so as to surround the air-fuel ratio sensor that is disposed downstream of the catalyst in the exhaust pipe. Thus, the sensor element in the protector cover is wetted and quenched, so that a difference in temperature between the heater and the air-fuel ratio sensor increases abruptly. As a result, the element of the air-fuel ratio sensor may crack due to thermal shock. Accordingly, in order to prevent the element from cracking due to thermal shock, it is important to detect a wet condition of the sensor element.
SUMMARY OF THE INVENTION
It is an object of the present invention to enhance precision in detecting a wet condition of a sensor element.
It is another object of the present invention to provide an oxygen concentration detector that prevents an element of an air-fuel ratio sensor from cracking due to the thermal shock resulting from the wetting of the element of the air-fuel ratio sensor when the air-fuel ratio sensor is preheated during, or prior to, the engine starting operation.
According to a first aspect of the present invention, an exemplary embodiment of an oxygen concentration detector includes an air-fuel ratio sensor, a heater that heats the air-fuel ratio sensor, a heater controller that supplies electric power to the heater such that the air-fuel ratio sensor reaches an activation temperature, and an element temperature detector that detects the temperature of an element of the air-fuel ratio sensor. The controller detects a rate of decrease in the element temperature of the air-fuel ratio sensor based on the temperature detected by the element temperature detector, and determines that the sensor element has been wetted when the detected rate of decrease is greater than a reference value. When wetting is detected, the controller controls the supply of electric power to the heater so as to attenuate thermal shock.
According to the first aspect of the present invention, upon detection of wetting of the sensor element, the supply of electric power to the heater is controlled so as to attenuate thermal shock. Therefore, the heater is prevented from being heated abruptly. Thus, the element of the air-fuel ratio sensor is prevented from cracking due to thermal shock resulting from an abrupt increase in the difference in temperature between the heater and the element of the air-fuel ratio sensor.
In the first aspect of the present invention, the element temperature detector can be configured to detect an element temperature of the air-fuel ratio sensor based on an element impedance of the air-fuel ratio sensor.
In the first aspect of the present invention, the heater controller can be configured to prohibit the heater from being supplied with electric power when it is determined that the sensor element has been wetted.
In the first aspect of the present invention, the air-fuel ratio sensor can be disposed in an exhaust passage of an internal combustion engine.
According to a second aspect of the present invention, an exemplary embodiment of an oxygen concentration detector includes an air-fuel ratio sensor provided in an exhaust pipe of an internal combustion engine, a heater that heats the air-fuel ratio sensor and a heater controller that supplies electric power to the heater such that the air-fuel ratio sensor reaches an activation temperature. The controller predicts whether an element of the air-fuel ratio sensor may be wetted, and limits the electric power supplied to the heater if it is predicted that the sensor element may be wetted.
According to the second aspect of the present invention, if it predicted that the sensor element may be wetted, the electric power supplied to the heater is limited. Therefore, the element is prevented from cracking due to thermal shock.
In the second aspect of the present invention, the prediction can based on determining whether water is disposed on a wall surface of the exhaust pipe.
In the second aspect of the present invention, the oxygen concentration detector may include a flow rate controller that reduces a flow rat
Ikeda Shinji
Suzuki Yusuke
Oliff & Berridg,e PLC
Toyota Jidosha & Kabushiki Kaisha
Wolfe Willis R.
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