Chemistry: electrical and wave energy – Apparatus – Electrolytic
Reexamination Certificate
1998-12-22
2001-07-10
Warden, Sr., Robert J. (Department: 1744)
Chemistry: electrical and wave energy
Apparatus
Electrolytic
C073S023320, C219S497000
Reexamination Certificate
active
06258232
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims priority from Japanese patent application Nos. Hei 9-358524 filed Dec. 25, 1997 and Hei 9-358525 filed Dec. 25, 1997, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a gas component concentration measuring apparatus, and more particularly, to a gas component concentration measuring apparatus for detecting an oxygen concentration in gases to be measured, such as exhaust gases from an engine.
2. Description of Related Art
In an automotive engine, for example, the air/fuel ratio control is generally executed based on a detection result of an oxygen concentration (or an air/fuel ratio) by an oxygen concentration sensor. This oxygen concentration sensor has a solid electrolyte made of zirconia, and the temperature of the sensor element (or the solid electrolyte) has to be kept at a predetermined activation temperature so as to detect the oxygen concentration (or the air/fuel ratio) accurately with the solid electrolyte. Usually, a heater is attached to the sensor thereby to control its activation. A method for this heater control, as known per se, is to control the electric power fed to the heater or to feedback-control the temperature of the sensor element to a predetermined activation temperature.
In the related art described above, however, at a cold start of the engine, for example, the sensor element (or the solid electrolyte) is increased as soon as possible from the cold state. However, if the temperature of the sensor element is rapidly increased, certain disadvantages, such as an element or heater cracking or a separation of the bonded faces of the element and the heater, may result.
Furthermore, in recent years, there is a tendency that a regulation on the exhaust gas component of the engine is intensified more and more from the standpoint of environmental protection, and it has been desired to improve the detection accuracy and durability of the oxygen concentration sensor. According to the aforementioned related art, however, the individual differences or aging of the sensor compromise the sensor accuracy. This problem is caused by an excess or shortage of the heater calorific power necessary for maintaining the sensor activation state. In other words, if the heater has a poor calorific power, the desired sensor activation state cannot be maintained, and the sensor detection accuracy is compromised. On the other hand, an excessive calorific power deteriorates the sensor element or the heater.
SUMMARY OF THE INVENTION
The present invention was made in light of the foregoing problems, and it is an object of the present invention to provide a gas component concentration measuring apparatus that maintains the sensor characteristics for the temperature increase and reduces the aforementioned-problems such as element cracking.
It is another object of the present invention to provide a gas component concentration measuring apparatus which improves the detection accuracy and durability by controlling the heater in a system which keeps the sensor active state with the heat of the heater.
The gas component concentration measuring apparatus of the present invention includes: a sensor for measuring the concentration of a specific component of gases, including a sensor element made of a solid electrolyte; a heater for heating the sensor element to a predetermined activation temperature, when activated by a power supply voltage; and a heater control circuit for controlling the current supply amount to the heater in accordance with the temperature increasing rate of the sensor element.
Accordingly, an excessive temperature increase in the sensor element can be suppressed by controlling the heater current while monitoring the temperature increasing rate of the sensor element. By monitoring the temperature increasing rate, moreover, a quick activation of the sensor is achieved. As a result, the sensor characteristics for temperature increase is satisfactorily maintained, and disadvantages such as element cracking is prevented.
The invention has a prominent effect especially in a laminated type sensor in which the heater is laminated on the sensor element having the solid electrolyte thereby to integrate the solid electrolyte and the heater. More specifically, the laminated type sensor may have problems such as element cracking or heater cracking because the solid electrolyte and the heater are located close to each other. According to the present invention, however, such problems are prevented.
The “temperature increasing rate of the sensor element” means a velocity of the temperature increase of the solid electrolyte or the heater. In order to control the temperature increasing rate of the sensor element, the heater current may be controlled according to the changing rate of the element temperature or the element resistance.
In order to control the temperature increasing rate of the sensor element, the heater current may be controlled according to the difference between the element temperature and the heater temperature.
In order to control the temperature increasing rate of the sensor element, the heater current may be controlled according to the changing rate of the heater temperature or the heater resistance.
According to another aspect of the present invention, it includes: a sensor including a sensor element made of a solid electrolyte for measuring the concentration of a specific component of gases; and a heater for generating heat when a current is supplied by a power supply. The sensor element is heated to a predetermined activation temperature by supplying the current to the heater. Supplying current to the heater is compensated according to a duration from the cold state to the activation of the sensor.
Accordingly, it is possible to control the current supply to the heater while considering the individual difference and aging of the sensor. Therefore, the control accuracy is improved. In short, when the sensor is deteriorated, the element temperatures (or the temperature of the solid electrolyte) before and after the deterioration differ even for an identical heater current control. According to the present invention, on the contrary, an unexpected fluctuation of the element temperature is reduced. As a result, the heater is controlled to improve the detection accuracy and the durability of the sensor.
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Hasegawa Jun
Mizoguchi Tomomichi
Takami Masayuki
Yamashita Yukihiro
Denso Corporation
Nixon & Vanderhye PC
Olsen Kaj K.
Warden, Sr. Robert J.
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