Oxygen Sensor: Description and Operation
DescriptionSystem Description:
Operation:
HO2S2 HEATER
System Description:
Operation:
HO2S3 HEATER
HO2S2
Component Description
The heated oxygen sensor 2, after TWC (Manifold three way catalyst), monitors the oxygen level in the exhaust gas.
Even if switching characteristics of air fuel ratio (A/F) sensor 1 are shifted, the air fuel ratio is controlled to stoichiometric by the signal from heated oxygen sensor 2.
This sensor is made of ceramic zirconia. The zirconia generates voltage from approximately 1V in richer conditions to 0V in leaner conditions.
Under normal conditions heated oxygen sensor 2 is not used for engine control operation.
HO2S3
Component Description
The heated oxygen sensor 3, after ADS-TWC (Adsorber pre-catalyst), monitors the oxygen level in the exhaust gas.
This sensor is used for recovery control of air fuel ratio after the fuel cut operation.
This sensor is made of ceramic zirconia. The zirconia generates voltage from approximately 1V in richer conditions to 0V in leaner conditions.
A/F SENSOR HEATER
Description
SYSTEM DESCRIPTION
The ECM performs ON/OFF duty control of the A/F sensor 1 heater corresponding to the engine operating condition to keep the temperature of A/F sensor 1 element at the specified range.
A/F SENSOR
Component Description
The A/F sensor is a planar dual-cell limit current sensor. The sensor element of the A/F sensor is the combination of a Nernst concentration cell (sensor cell) with an oxygen-pump cell, which transports ions. It has a heater in the element.
The sensor is capable of precise measurement lambda = 1, but also in the lean and rich range. Together with its control electronics, the sensor outputs a clear, continuous signal throughout a wide lambda range (0.7 < lambda < air).
The exhaust gas components diffuse through the diffusion gap at the electrode of the oxygen pump and Nernst concentration cell, where they are brought to thermodynamic balance.
An electronic circuit controls the pump current through the oxygen-pump cell so that the composition of the exhaust gas in the diffusion gap remains constant at lambda = 1. Therefore, the A/F sensor is able to indicate air/fuel ratio by this pumping of current. In addition, a heater is integrated in the sensor to ensure the required operating temperature of 700 - 800 °C (1,292 - 1,472 °F).