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Automobile knowledge, engine oxygen sensor

I. Overview

The sensor can be used to provide information about whether there is excessive oxygen in the exhaust gas after combustion. According to this information, the electronic controller carries out closed-loop control on the fuel injection quantity, so that the three main toxic components HC, CO and NOX in the exhaust gas can be converted and purified to the greatest extent by the three-way catalyst.

Second, the structure

The outside of the oxygen sensor electrode is in the exhaust gas flow, while the inside is communicated with the surrounding air. The inner core of oxygen sensor is airtight zirconia ceramic body, and the surface of the inner core is a very thin and breathable platinum layer. On the one hand, the platinum layer plays a catalytic role, on the other hand, it also plays the role of a physical electrode. Outside the platinum layer is a very hard porous ceramic layer, which can protect the platinum layer from the damage of exhaust gas flow in addition to air permeability.

1- zirconia ceramic body, 2- platinum layer, 3- inner joint, 4- outer joint, 5- exhaust pipe, 6- porous ceramic, 7- exhaust pipe, 8- air.

Third, principles.

According to Nernst principle, when heating, the sensor absorbs oxygen in the air by using the porous characteristics of ceramic body and electrolyzes it, which can generate potential difference according to the different oxygen content inside and outside the oxygen sensor. By measuring the potential difference, the residual oxygen content in the current exhaust gas can be obtained. Because the residual oxygen content in the nearby exhaust gas changes obviously, the output voltage of the nearby oxygen sensor will jump.

Fourth, installation

The position of the oxygen sensor installed on the exhaust pipe should not only reflect the exhaust composition of all cylinders, but also have a high enough temperature: the unheated sensor should work above 350℃; The heating sensor should work at 150℃.

Verb (abbreviation of verb) characteristics

1, when the mixture is thinner than 1, the output value is1100mv (except LSU type).

2. Long-term exposure to excessive exhaust temperature will slow down the response speed of oxygen sensor to the change of air-fuel ratio, which will delay the response of two-state control and prolong the change period. A diagnostic function module in the electronic controller is responsible for monitoring the frequency of this control response. When it is found that the response of the oxygen sensor is too late, it will light a diagnostic lamp to warn the driver.

Sixth, characteristics

1, which can still work at low exhaust temperature (such as idle speed), thus effectively realizing closed-loop control;

2. More flexible installation position;

3. enter the working state faster;

4. More sensitive dynamic response ability;

5, the anti-pollution ability is stronger;

6. The service life is longer, ≥ 160000km.

Seven, attention

1. The installation angle of the oxygen sensor should be greater than or equal to 10, with its tip facing downwards, so as to avoid condensation between the sensor housing and the sensor ceramics during cold start;

2. Do not heat the metal buckle of the cable on the oxygen sensor side, otherwise it will burn out the cable and cause short circuit;

3. Do not use cleaning liquid, oily liquid or volatile solid on the oxygen sensor plug;

4. Please tighten according to the required torque (50~60Nm).

Eight, detection skills

1. oxygen sensor (except LSU type) works normally. When the system is in λ closed-loop control, the signal voltage measured by adapter and multimeter should change repeatedly within the range of 0. 1~0.9V, and the change frequency is about ten or twenty times per minute.

2. If the output signal is always fixed at about 0.45V, or changes slowly, or the signal is always in the range of 0.5~0.9V, or always fluctuates in the range of 0. 1~0.5V, it means that the system is still not working normally, and the reason must be found.