The oxygen concentration sensor or lambda probe is designed to determine the level of oxygen in the exhaust gas. Efficient (environmentally friendly and economical) motor operation is ensured by a constant level of correlation in the fuel mixture of fuel and air in all operating modes. The process of controlling the oxygen content in the exhaust gas is called lambda control.
If there is a lack of air-fuel mixture, the complete oxidation of carbon monoxide and hydrocarbons does not occur. In case of air supersaturation, on the other hand, complete decomposition into oxygen and nitrogen does not occur.
In the exhaust system, a lambda probe is installed. It should be said that on certain models of machines not one oxygen sensor is used, but two. In this case, one is installed behind the catalytic converter, and the other after. The use of two sensors helps to strengthen control over the composition of the exhaust gases and ensure the most efficient operation of the converter.
The oxygen sensor may be point-to-point or broadband.
The first is installed after the converter, and before it. A two-point oxygen sensor detects the excess air coefficient of the fuel air mixture in accordance with the concentration of oxygen in the exhaust gases.
The design is presented in the form of a ceramic element, which has a double-sided coating of zirconia. The oxygen sensor is checked by the electrochemical method. On one side, the electrode is in contact with exhaust gases. On the other hand, with the atmosphere. With a different oxygen content, voltage is created at the ends of the electrode. The higher the level (the fuel mixture is considered lean), the lower the voltage. Accordingly, the higher the concentration (the mixture is considered enriched), the greater the voltage.
An oxygen sensor sends an electrical signal to an electronic control unit in the motor control system. In accordance with the signal level, the executive structures of those systems in the vehicle that are controlled by this control unit are affected.
The design of the broadband sensor is presented as an injection and two-point element. The determination of the value of "lambda" is carried out using current when pumping. This device is used as an input oxygen sensor of the catalytic converter. By injection is meant a process of a physical nature. During pumping from gases, oxygen passes through the pumping element under the influence of current. The principle by which the device operates is based on the ability to constantly maintain a voltage of 450 mV in a point-to-point element between the electrodes due to a change in current when pumped.
A decrease in the oxygen content in gases (with an enriched fuel mixture) is accompanied by an increase in voltage between the electrodes present in a two-point ceramic element. The signal is supplied from the element to the electronic control unit. Based on the signal on the pumping element, a current is generated with a certain force.
In turn, current facilitates pumping into the measurement gap. The voltage thus reaches a certain value. In this case, the indicator of current strength is a measure of the concentration of oxygen in gases. Analysis and conversion into control actions on execution devices in the injection system is carried out by the control unit.
With a lean fuel mixture, the operation of the broadband device is similar. The difference is that oxygen is pumped out from the measuring gap under the influence of current.