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Oxygen Sensor The Main Role Introduced

Nov 03, 2017

The oxygen sensor is standard on the car, using the Nernst principle. It is the use of ceramic sensitive components of the car exhaust pipe oxygen potential measured by the chemical equilibrium principle to calculate the corresponding oxygen concentration to achieve the monitoring and control of combustion air-fuel ratio to ensure product quality and exhaust emissions compliance measurement components. Has the advantages of simple structure, rapid response, easy maintenance, easy to use, accurate measurement and so on.

On engines that use three-way catalytic converters to reduce exhaust pollution, oxygen sensors are an essential element. Since the air-fuel ratio of the mixture deviates from the stoichiometric air-fuel ratio once and for all, the purification ability of the three-way catalyst for CO, HC and NOx will be drastically reduced. Therefore, an oxygen sensor is installed in the exhaust pipe to detect the oxygen concentration in the exhaust gas, ECU sends out the feedback signal, then the ECU controls the fuel injection amount of the injector to increase or decrease, thus controls the air-fuel ratio of the mixture near the theoretical value.

main effect 

EFI vehicles must use three-way catalytic converters to achieve high exhaust gas purification rates and to reduce the amount of (CO) carbon monoxide, (HC) hydrocarbons and (NOx) nitrogen oxides in the exhaust gas. However, in order to effectively use the three-way catalyst, it is necessary to precisely control the air-fuel ratio so that it always approaches the stoichiometric air-fuel ratio. The catalyst is usually installed between the exhaust manifold and the muffler. Oxygen sensors have a characteristic that the voltage they output abruptly changes near the theoretical air-fuel ratio (14.7: 1). This feature is used to detect the concentration of oxygen in the exhaust gas and fed back to the computer to control the air-fuel ratio. When the actual air-fuel ratio becomes high, the oxygen concentration in the exhaust gas increases and the oxygen sensor informs the ECU that the air-fuel mixture is lean (low electromotive force: 0 volts). When the air-fuel ratio is lower than the stoichiometric, the concentration of oxygen in the exhaust gas decreases and the state of the oxygen sensor (large electromotive force: 1 volt) is notified to the ECU computer.

The ECU determines the low or high air-fuel ratio based on the difference in electromotive force from the oxygen sensor and controls the duration of fuel injection accordingly. However, if the oxygen sensor is faulty and the output electromotive force is abnormal, the ECU can not precisely control the air-fuel ratio. So the oxygen sensor can make up for the mechanical and EFI system due to wear and tear caused by air-fuel ratio error. It can be said that the only "smart" sensor in the EFI system.

The role of the sensor is to determine whether there is an excess of oxygen in the exhaust after the engine is burned, ie the oxygen content and convert the oxygen content into a voltage signal for transmission to the engine computer enabling the engine to achieve closed-loop control with an excess air factor; The three-way catalytic converter has the maximum conversion efficiency for the three pollutants (HC, CO and NOX) in the exhaust gas to maximize the conversion and purification of the pollutants discharged .

Oxygen sensor is a standard car, it is the use of ceramic sensors to measure the oxygen in the car exhaust pipe oxygen balance calculated by the principle of chemical oxygen corresponding to the monitoring and control of combustion air-fuel ratio to ensure product quality and tail gas Emission of standard measuring components. Oxygen sensor is widely used in various types of furnace control such as coal combustion, oil combustion and gas combustion. It is the best measurement method of combustion atmosphere at present. It has the advantages of simple structure, rapid response, easy maintenance, convenient operation and accurate measurement . The use of the sensor for combustion atmosphere measurement and control can not only stabilize and improve product quality, but also shorten the production cycle and save energy.

The oxygen sensor in the car works like a dry cell battery, with the zirconia element in the sensor functioning like an electrolyte. Its basic working principle is: under certain conditions, the use of oxygen concentration on both sides of the zirconia difference between the potential difference, and the greater the concentration difference, the greater the potential difference. The content of oxygen in the atmosphere is 21%. The exhaust gas after the rich-mixture combustion does not actually contain oxygen. The exhaust gas generated by the combustion of the lean mixture or the exhaust gas generated by lack of fire contains more oxygen than the atmospheric Much less oxygen. Under high temperature and platinum catalysis, negatively charged oxygen ions are adsorbed on the inner and outer surfaces of the zirconia sleeve. Since oxygen in the atmosphere is more than oxygen in the exhaust gas, more negative ions are adsorbed on the side of the casing that communicates with the atmosphere than on the exhaust gas side, and the ion concentration difference between the two sides produces electromotive force.

When the oxygen concentration on the exhaust side of the bushing is low, a high voltage (0.6 to 1 V) is generated between the oxygen sensor electrodes. The voltage signal is sent to the automotive ECU for amplification. The ECU sees the high voltage signal as a rich gas , And the low voltage signal as a lean mixture. Depending on the voltage signal of the oxygen sensor, the computer dilutes or enriches the mixture at a theoretical optimum air-fuel ratio as close as possible to 14.7: 1. The oxygen sensor is therefore the key sensor for electronically controlled fuel metering. Oxygen sensor only in high temperature (end of 300 ° C or more) its characteristics can be fully reflected in order to output voltage. It responds most rapidly to changes in the mixture at about 800 ° C, but greatly changes at low temperatures.