Foreword This article refers to the address: http:// Cars bring great convenience to people's lives, but car exhaust pollution has polluted our living environment. With the introduction of automobile emission regulations, car oxygen sensors that can effectively reduce emissions have been created. The role of the car's oxygen sensor is to get the best concentration of the mixture in the engine, so as to reduce the emission of harmful gases and save fuel. This paper introduces the role of automotive oxygen sensors and analyzes the failure of automotive oxygen sensors with examples. 1, the role of automotive oxygen sensors The function of the car's oxygen sensor is to determine whether the oxygen in the exhaust gas after combustion of the engine is excessive, that is, the oxygen content, and convert the oxygen content into a voltage signal and transmit it to the engine computer, so that the engine can achieve excess air factor (λ=1). Closed-loop control for the target; ensure that the three-way catalytic converter has the maximum conversion efficiency for the three pollutants of hydrocarbon (HC), carbon monoxide (CO) and nitrogen oxides (NOX) in the exhaust gas, and maximizes the conversion efficiency. Conversion and purification of pollutants discharged. The automotive oxygen sensor is used to detect the state of the exhaust gas entering the three-way catalytic converter, and is an indispensable sensor on the engine using a three-way catalytic converter. Once the air-fuel ratio of the engine deviates from the theoretical air-fuel ratio, the purification ability of the three-way catalyst for CO, HC and NOx will drop drastically. Therefore, in order to achieve optimum exhaust gas purification performance of an engine equipped with a three-way catalytic converter, the air-fuel ratio of the mixture must be controlled within a narrow range near the theoretical air-fuel ratio. Oxygen sensors currently used in automobiles are available in both zirconia and titania. 2. The role of automotive oxygen sensors in electric vehicles The oxygen sensor detects the oxygen concentration in the exhaust gas at any time and feeds back the signal to the microcomputer control device at any time. The microcomputer adjusts the fuel injection amount (injection pulse width) according to the feedback signal. If the signal reflects that the mixture is richer, the injection time is reduced. Conversely, if the signal is relatively thin, the injection time is prolonged. Therefore, the air-fuel ratio of the mixture is always maintained at the theoretical air-fuel ratio and always maintained near the theoretical air-fuel ratio. This is the fuel closed loop control or fuel feedback control.  Commonly used oxygen sensors are zirconia and titanium oxide. Taking the zirconia type as an example, the voltage signal of the oxygen sensor normally fluctuates between 0 and 1 V when the closed-loop control is performed, and the average value is about 450 mV. When the concentration of the mixed gas is slightly richer than the stoichiometric air-fuel ratio, the oxygen sensor generates a high voltage signal of about 800 mV; when the mixture concentration is slightly thinner than the stoichiometric air-fuel ratio, the oxygen sensor generates a low voltage signal close to 100 mV. Therefore, it can be said that the oxygen sensor is a "communicator" who feeds back the air-fuel ratio information to the microcomputer at any time. 3, car oxygen sensor detection The engine ECU monitors the oxygen sensor signal and adjusts the fuel supply amount according to the oxygen sensor signal voltage. If the oxygen sensor signal is abnormal, set the fault code. When checking the oxygen sensor, it should be noted that the voltage value of the main oxygen sensor varies between 0.1V and 0.9V, and the voltage value of the sub-oxygen sensor fluctuates between 0.5V and 0.7V. An abnormality in the oxygen sensor signal is not necessarily a malfunction of the oxygen sensor. Do not blindly replace the oxygen sensor. Checking the oxygen sensor signal voltage or waveform is normal is the key to such fault diagnosis. The oxygen sensor signal waveform should be observed first with an oscilloscope. When the engine burns the rich mixture, the oxygen sensor voltage can reach 0.8V or higher. When the engine burns the lean mixture, the oxygen sensor voltage can drop below 0.2V, and the performance of the oxygen sensor can be determined. good. Case Analysis of Automotive Oxygen Sensor Failure In the practice of repair, you will often encounter examples of faults in the oxygen sensor. The following describes the method of detecting and repairing the fault of the oxygen sensor in combination with a case encountered in the work. 3.1 Failure phenomenon A Toyota LEXUS LS400 sedan has ran more than 100,000 kilometers. The owner of the car reported that the acceleration of the car was not smooth before, and the idle speed of the throttle was slight. When the engine failed, the engine did not light up and the fuel consumption increased significantly. So came to our factory for testing and maintenance. 3.2 Fault Detection and Diagnosis After receiving the car, I conducted a preliminary inspection of the car according to the situation reflected by the owner. Perform self-diagnosis and read the fault code. The fault code indicates that the mixture is too rich or too lean, so that the approximate fault location is in the intake system, fuel supply system, and ignition system. Possible major fault components are air flow meters, water temperature sensors, throttle position sensors, oil pressure regulators, point coils, high voltage lines, spark plugs, and oxygen sensors. The test is carried out one by one according to the principle of easy and difficult, and the fault is inferred. Because the air flow meter, water temperature sensor, and throttle position sensor all have a certain fault code, if there is a problem, it will be recorded by the control unit, and the fault code will be read. According to the fault self-diagnosis, these parts have no fault code. Basically, it can be determined that the appeal component is not faulty. The oxygen sensor is a component that is affected by other factors. The other components should be detected first, and finally the oxygen sensor. a) Overhaul of the intake system The most common fault in the intake system is the blockage of the air filter, which causes the intake air to be insufficient, causing the combustible mixture to be too rich, causing the engine to accelerate, the fuel consumption is increased, and the like. After dismantling and checking, it was found to be a bit dirty, but not too serious. After it was blown clean and put back, the engine was started and the vacuum of the idle intake manifold was measured and found to be 62 kPa. Meet the requirements. The air intake system is well sealed and the engine seal is normal. The possibility of engine mechanical failure is ruled out. b) Fuel supply system overhaul If the fuel pressure is too high or too low, the injector will not work properly and will cause the above failure. The fuel pressure idle speed was measured by a gasoline pressure gauge to be 225 kPa. After parking, short-circuit the electric gasoline pump two check terminals Fp and +B6, the measured static oil pressure is 304kPa, and the fuel system holding pressure is 196kPa after 5 minutes. The electric gasoline pump works well and the injector has no leakage. Remove the injector test, the fuel injection and fuel injection conditions are no problem, the fault is not here. c) Ignition system overhaul Improper operation of the ignition system can result in insufficient combustion, reduced engine power, and increased fuel consumption. The spark, the cylinder line, the split head, and the high-voltage coil were removed for inspection. It was found that except for the platinum spark plug which was somewhat black and the electrode was ablated, the others were within the technical requirements. The vehicle has traveled more than 100,000 Km, and the spark plug ablation is not surprising, but blackening is caused by insufficient combustion or excessive mixture. Further inspection revealed that the eight spark plugs were all the same and very uniform, which may be caused by poor engine fuel injection control. d) Overhaul of oxygen sensor According to the circuit diagram, disconnect the engine ECU and the oxygen sensor, detect the oxygen sensor, and measure the resistance of the heating element of the main oxygen sensor on both sides of the left and right sides, both between 5.1 and 6.3 Ω, no problem, then measure the ECU terminals HTL and HTR. There is no problem with the voltage of the grounding iron between 9 and 14V. Only check the operation of the oxygen sensor. Assemble the removed parts as required, start the engine, and heat the car to the normal working temperature, connect the E1 and te1 terminals on the diagnostic socket, and connect the VF1 and VF2 terminals of the socket with the positive meter of the multimeter. The watch rod was connected to E1, operated at high idle (2500 r/min) for 2 minutes to heat the oxygen sensor, and then the engine speed was maintained at 2500 r/min. Calculate the number of fluctuations of the meter between 0 and 5V (normally should fluctuate about 8 times every 10 seconds), and the measured number of fluctuations is zero. Always at 0V, the problem may be an oxygen sensor signal problem. Then measure the voltage between the terminal OX1, OX2 terminal and E1 is below 0.5V, only 0.1~0.2V (normal should be above 0.5V), which means that the oxygen sensor does not work, the problem is finally found. Since the oxygen sensor can not normally feed back the signal to the engine ECU, the fuel injection width of the injector cannot be controlled and corrected, resulting in a mixture that is too thin and too rich, resulting in a promising problem. After the final replacement of the two oxygen sensors and the spark plug, the test drive failure never occurred again. Conclusion The function of the oxygen sensor is to determine whether the oxygen in the exhaust gas after combustion of the engine is excessive, and to maximize the conversion and purification of the discharged pollutants. Since the oxygen sensor is installed on the high-temperature exhaust pipe, the working environment is bad, and the output signal is inaccurate after a long time. Therefore, the oxygen sensor must be inspected at a certain time, otherwise the fuel control system cannot be accurately controlled.
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