James Lamar Freeman

US Patent:

6409969, Jun 25, 2002

Filed:

Jun 1, 1999

Appl. No.:

09/323199

Inventors:

Steven R. Streicher - Cincinnati OH
James A. Freeman - Antioch IL
John E. Taylor - Columbus IN

Assignee:

Cummins, Inc. - Columbus IN

International Classification:

G01N 3112

US Classification:

422 94, 422 98, 422 83

Abstract:

The present invention contemplates a system and method for controlling or adjusting the accuracy of an exhaust gas sensor utilizing the impedance of the sensing element. In one embodiment, a periodic AC signal is superimposed over low frequency or DC output signal produced by the gas sensor. The AC current flowing through the gas sensor is a function of the actual impedance of the sensor, which is in turn a function of the temperature of the sensor. Thus, the invention further contemplates an impedance sensor circuit connected to an output of the gas sensor. The output of the impedance sensor circuit is a peak voltage that is indicative of the AC voltage drop across the sensor, and ultimately the impedance of the sensing element. This peak voltage is utilized to control the operation of the heating element in a closed loop control system in which the thermal output of the heating element is continuously varied as a function of the magnitude signal to accurately maintain a consistent temperature for the exhaust gas sensor. In a specific embodiment of the invention, the impedance sensor circuitry includes a bandpass filter centered around the frequency of the superimposed AC signal to eliminate spurious noise.