Oxygen sensor monitoring a deterioration of a three-way ... - UMEL

4 K. Moriya, T. Sako / Sensors and Actuators B 3646 (2000) 1–10
Table 3
Gas composition for response measurement
Stage
Gas concentration(vol.%/N 2 base)
CO 2 CO H 2 O 2 CH 4
Lean 11.300 0.079 0.048 0.624 0.138
Rich 11.300 0.758 0.493 0.451 0.163
3. Results and discussion
3.1. Deterioration of oxygen sensors
As shown in Fig. 5, in this sensor, a YSZ is sintered into a
tube shape and electrodes were formed on both sides by
plasma spraying process. The YSZ tube is installed in a
metal case and lead wires from the electrodes are settled by
Fig. 3. Schematic diagram of the sensor response measurement apparatus.
Fig. 4. Structures of the stainless holder for response measurement.
waterproof sealing rubber on the metal case. Table 2 lists the
compositions of the ashes blown onto the sensor case. As
indicated in the table, the compositions and their amounts
varied with the lubrication oil type but they did not affect on
the sensor characteristics. Table 4 shows the inner resistance
and the rapid rising points (the values of equivalence ratio
when the sensor outputs were 0.45–0.7 V). Fig. 6 indicates
typical response curves. Sensors a1, b1 and c1 in Table 4
were new. Sensors a2 through a5, b2, c2 and c3 were used for
many or several hours in actual applications, but their inner
resistance and the rapid rising points were close to those of
the new sensors. Other sensors (degraded sensors) had
higher internal resistance than the new sensors, and the
rapid rising points were different. In all cases where the
sensor characteristics showed deviations, the system performances
were low. But even when the characteristics of
sensor was same as the new sensor’s, the performance of
UNCORRECTED PROOF