In the exhaust gas, the oxygen sensor has specific voltage output characteristics, and when the air-fuel ratio is close to the theoretical air-fuel ratio, its output voltage will change abruptly. This characteristic is used to detect the concentration of oxygen in the exhaust gas, and the result is fed back to the ECU of the vehicle to realize the control of the air-fuel ratio.

This article will introduce the role of oxygen sensors and their importance in automotive emission control, while explaining the classification of oxygen sensors in detail, including classification by material, classification by signal characteristics, and presence or absence of heating. Understanding the different types and characteristics of oxygen sensors will help to better understand their use in automotive emission control systems.

What is the role of the oxygen sensor

The role of oxygen sensors is to detect the oxygen content in the exhaust gas to determine the concentration of the mixed gas and feed it back to the ECU. In order to obtain a high exhaust gas purification rate and reduce the components of (CO) carbon monoxide, (HC) hydrocarbons and (NOx) nitrogen oxides in the exhaust, EFI vehicles must use three-way catalytic converters. But in order to effectively use the three-way catalytic converter, the air-fuel ratio must be precisely controlled so that it is always close to the theoretical air-fuel ratio. The catalytic converter is usually installed between the exhaust manifold and the muffler. The oxygen sensor has a characteristic that its output voltage has a sudden change near the theoretical air-fuel ratio (14.7:1). This characteristic is used to detect the concentration of oxygen in the exhaust and feed it back to the computer to control the air-fuel ratio.

When the actual air-fuel ratio becomes higher, the concentration of oxygen in the exhaust gas increases and the oxygen sensor notifies the ECU of the lean state of the mixture (small electromotive force: 0 volts). When the air-fuel ratio is lower than the theoretical air-fuel ratio, the concentration of oxygen in the exhaust gas decreases, and the state of the oxygen sensor (large electromotive force: 1 volt) notifies the (ECU) computer.

Classification of oxygen sensors

2-1 Divided by material: Titanium oxide type, Zirconia type

a. Titanium oxide oxygen sensor is made of the characteristic that the resistance value of titanium dioxide material changes with the change of oxygen content in the exhaust gas, so it is also called resistive oxygen sensor

b. The basic element of the zirconia oxygen sensor is the zirconia ceramic tube (solid electrolyte), also known as the zirconia tube

According to the number of wires behind the oxygen sensor, it can be divided into: 2 wires, 3 wires, 4 wires, 5 wires, 6 wires, etc.

2-2 According to the signal characteristics of the oxygen sensor, it can be divided into: narrow range (jump type) and wide range (broadband type).

2-3 According to whether there is heating in the oxygen sensor, it can be divided into heating type and non-heating type. The traditional oxygen sensor is not equipped with heating, and all the currently used ones are equipped with heating. Otherwise, the oxygen sensor cannot quickly reach normal working conditions after starting for a period of time, which is not in compliance with national regulations.