PGM-FI System Description - A/F Sensor/HO2S Feedback Air/Fuel Ratio Control

Air fuel ratio control is part of fuel injection control and comprises the steps of:

	Calculating basic injection amount from intake air flow amount and engine speed
	Calculating air fuel ratio correction value from the oxygen density in the exhaust gas and reflecting the calculated values to the injection amount

Air fuel ratio control stops feedback under the following conditions in order to maintain operational performance and catalytic protection.

	When starting the engine or during fuel increase after the engine is started
	While the engine coolant is cold
	During fuel increase under high load
	During fuel increase at high engine speed
	During fuel cut-off at deceleration

Air Fuel Ratio (A/F) Sensor (Sensor 1)

The air fuel ratio (A/F) sensor (Sensor 1) is installed on the warm up three way catalytic converter (WU-TWC). Air fuel ratio control performs fuel injection control based on the oxygen density detected in exhaust gas in order to bring the intake mixture in the vicinity of a target air fuel ratio.
This high-precision air fuel ratio control is realized by detecting a correction value with an A/F sensor (Sensor 1) and then applying further correction with a secondary heated oxygen sensor (secondary HO2S) (Sensor 2).
The sensor element and the heater inside the A/F sensor (Sensor 1) have a layered construction of a plate-shaped zirconia element whose inside and outside are coated with platinum and a built-in platinum heater.
A ceramic coating diffusion layer on the platinum electrode on the outside of the element creates an atmospheric chamber between the platinum electrode inside the element and the heater.

Secondary HO2S (Sensor 2)

The secondary heated oxygen sensor (secondary HO2S) (Sensor 2) is installed downstream of the warm up three way catalytic converter (WU-TWC), and it detects the oxygen density in the exhaust gas passing through the catalyst and outputs it to the powertrain control module (PCM) to enable the high-precision air fuel ratio control, which cannot be realized only with an A/F sensor (Sensor 1).
Inside secondary HO2S (Sensor 2) is a test tube shaped zirconia element whose inside and outside surfaces are coated with platinum. The inside surface is exposed to the atmosphere, while the outside surface is within the exhaust gas.
A ceramic heater is equipped inside the element in order to shorten sensor reaction time and to enable output that is constantly stable.