Oxygen concentration sensing apparatus

• US 4,804,454 A
• Filed: 03/19/1987
• Issued: 02/14/1989
• Est. Priority Date: 03/19/1986
• Status: Expired due to Term

• Current Assignee: Honda Giken Kogyo Kabushiki Kaisha (Honda Motor Company)
• Original Assignee: Honda Giken Kogyo Kabushiki Kaisha (Honda Motor Company)
• Inventors: Muroya, Minoru, Asakura, Masahiko, Seki, Yasunari, Shiina, Takanori
• Primary Examiner(s): NOT, DEFINED
• Assistant Examiner(s): Hsing, Ben C.
• Application Number:
  US07/028,138
• Time in Patent Office: 698 Days
• Field of Search: 204/1 T, 204/406, 204/410-412, 204/425-426
• US Class Current: 204/406
• CPC Class Codes: G01N 27/4065 Circuit arrangements specially adapted therefor
• CPC Class Codes: G01N 27/417 using cells , i.e. more than one cell and probes with solid electrolytes

Abstract

An oxygen concentration sensing apparatus includes an oxygen pump element and a sensor cell element to be placed in a gas under measurement, and a device for generating a voltage value command indicating a voltage to be generated across electrodes of the sensor cell element. A current limit device is provided so that the supply of the voltage value command is stopped to decrease a pump current to the oxygen pump element gradually when the voltage generated across the electrodes of the sensor cell element exceeds a first predetermined voltage, and the pump current to the oxygen pump element is reduced immediately when the voltage generated across the electrodes of the sensor cell element exceeds a second predetermined voltage which is higher than the first predetermined voltage.

Claims

1. An oxygen concentration sensing apparatus comprising:

oxygen sensing means, responsive to oxygen in a gas under measurement, for producing an output signal having a magnitude proportional to the concentration of oxygen in the gas under measurement when contacted by a stream of the gas, said oxygen sensing means having,

a sensor cell element made of a first active plate of an oxygen ion conductive solid electrolyte and a first pair of electrodes sandwiching said first active plate,

an oxygen pump element made of a second active plate of an oxygen-ion conductive solid electrolyte and a second pair of electrodes sandwiching said second active plate,

said first and second active plates defining a restricted region into which said gas under measurement is introduced;

command generating means for generating a voltage value command representing a voltage to be generated across said first pair of electrodes of said sensor cell element;

delay means for gradually supplying said voltage value command supplied by said command generating means;

current supply means, responsive to said gradually supplied voltage value command received from said delay means, for supplying a pump current across said second pair of electrodes of said oxygen pump element so that a voltage generated across said electrodes of said sensor cell element equals said voltage represented by said voltage value command, said current supply means further developing a current value of said pump current supplied to said oxygen pump element as said output signal indicating the measured oxygen concentration; and

limit means for stopping the supply of an excess current to said electrodes of said oxygen pump element by said current supply means, said limit means including,

first switch means for stopping the supply of said voltage value command from said command generating means to said delay means when said voltage generated across said electrodes of said sensor cell element exceeds a first predetermined voltage, and

second switch means for immediately reducing said pump current across said electrodes of said oxygen pump element when said voltage generated across said electrodes of said sensor cell element exceeds a second predetermined voltage which is higher than said first predetermined voltage.

2. An oxygen concentration sensing apparatus as set forth in claim 1, wherein said delay means comprises a charge-discharge circuit whose output signal level increases gradually when the voltage value command is supplied from said command generation means, and decreases gradually when said supply of said voltage value command is stopped by said first switch means.

3. The oxygen concentration sensing apparatus of claim 2 wherein said first switch means gradually reduces said pump current by stopping the supply of said voltage value command to said delay means.

4. The oxygen concentration sensing apparatus of claim 1 wherein said gas under measurement is the exhaust of an internal combustion engine.