Broad-band Lambda Oxygen
    Sensor

A probe technology which focuses exclusively on one ideal point is outdated. You may think of petrol direct fuel injection engines featuring a stratified charge operation or diesel engines for which the control unit should regulate a meagre combustion. In these cases a broad-band lambda oxygen sensor is necessary. By the way, other industrial branches make use of this technology, too.

The planar technology is a prerequisite for the development of the broadband probe. Another chamber is added with an opening to the exhaust gas pipe. This chamber also receives two conductive foils. With it the broadband probe has 5 connections, sometimes 4. Two for the heating and one (together with ground) for the lambda oxygen sensor current.There are two additional connections: they regulate the admission of rest oxygen from the exhaust gas via a small opening to the so-called pumping cell. Both conducting foils are positioned in such a way that via a certain current flow the attractiveness for the negatively charged oxygen ions can be controlled. It is again aimed at a lambda of 1 in the pump cell; as much rest oxygen should stay in the pump cell, as is necessary for a Lambda value of 1.

The diagramme shows it clearly. If a Lambda value of 1 is determined between the layer borders of the pumping cell and the measuring space, nothing at all happens. If values of more than 1 are observed, oxygen is "pumped" (meagre) outwards, with values less than 1, new oxygen from the exhaust gas is attracted. The pumping electricity is a measure of the Lambda in the combustion. The control unit calculates the actual Lambda according to the current used for pumping. See the figure above. Continuous co-operation between the sensor and the control unit is necessary, to determine the Lambda value of a combustion mixture. There are, in the meantime, lambda oxygen sensors with access times of few milliseconds. They are able to determine the mixture ratios in the single cylinders.