Functional description

The sensor system of the broadband oxygen sensor consists of ceramic layers of zirconium dioxide (laminate). The heating element inserted in the laminate rapidly ensures the required operating temperature of at least 760 °C. The broadband oxygen sensor has 2 cells, a so-called measurement cell and a reference cell. The two cells are coated with electrode made of platinum.

Fig 1: Identifying Broadband Oxygen Sensor, Housing And Plug Connection

Courtesy of BMW OF NORTH AMERICA, INC.

Example schematic diagram

The broadband oxygen sensor can be used to continuously measure an air/fuel ratio between 0.65 and pure air (constant characteristic curve). The broadband oxygen sensor is operational in a shorter time than the predecessor LSU 4.9 version. For complete and perfect combustion, a air/fuel ratio of 1 kilogram of fuel and approx. 14.7 kilograms of air is necessary. The ratio between the air quantity that is actually being supplied and that required for a stoichiometric ratio is designated as lambda. During normal operation of the vehicle, the Lambda value fluctuates. The engine has its best performance with a lack of air (Lambda approx. 0.9 = rich mixture). The engine has its lowest consumption with excess air (Lambda approx. 1.1 = lean mixture). The catalytic converter can most effectively reduce pollutant emissions if the fuel-air mixture is in the region of Lambda = 1. The conversion rate, i.e. the proportion of converted pollutants, is 98 % to virtually 100 % in the case of modern catalytic converters. The optimum composition of the fuel-air mixture is regulated by the engine control. The oxygen sensors deliver essential information on the composition of the exhaust gas.