Development of High Accuracy Rear A/F Sensor 2017-01-0949
New 2A/F systems different from usual A/F-O2 systems are being developed to cope with strict regulation of exhaust gas. In the 2A/F systems, 2A/F sensors are equipped in front and rear of a three-way catalyst. The A/F-O2 systems are ideas which use a rear O2 to detect exhaust gas leaked from three-way catalyst early and feed back. On the other hand, the 2A/F systems are ideas which use a rear A/F sensor to detect nearly stoichiometric gas discharged from the three-way catalyst accurately, and to prevent leakage of exhaust gas from the three-way catalyst. Therefore, accurate detection of nearly stoichiometric gas by the rear A/F sensor is the most importrant for the 2A/F systems. In general, the A/F sensors can be classified into two types, so called, one-cell type and two-cell type. Because the one-cell type A/F sensors don’t have hysteresis, they have potential for higher accuracy. In addition, in rear environment, because there are very much condensed water in an exhaust pipe, thimble typed sensors which are resistant to water splash are suitable. For these reasons, we consider one-cell type A/F sensor for the rear, using a thimble typed sensor which are resistant to water splash for the first time in the world. We developed the rear-A/F sensor highly accurate for stoichiometric gas successfully, and we report these technologies.