Breakthrough for the catalytic converter
Catalytic converters have existed in North America since the mid-1970s. To begin with, they filtered up to 50% of emissions. But Bosch engineers were not satisfied with the level of efficiency. They realized that improvements were only possible if the composition of the fuel-air mixture in the fuel injectors was precisely adapted to the filtering ability of the catalytic converter. One good indicator for an ideal fuel-air mixture is the proportion of residual oxygen in exhaust emissions. And that is precisely what Lambda probes measure.

It is also why they are sometimes called "Oxygen sensors", or simply "O2 sensors". The more commonly used "Lambda probe" comes from the Greek letter Lambda, which technicians use to describe the volume of air in the fuel-air mixture. In 1976, the invention and use of Lambda probes transformed uncontrolled catalytic converters into controlled three-way catalytic converters with a filtering efficiency of over 90%. The new technology was an overnight success, first in the USA and then in Europe.

The probe is perfected
The first probes had a relatively simple structure and were unheated. The exhaust gases had to heat up the probes before they could deliver exact data. That could take a few minutes. But Bosch technicians wanted more. In the 1980s, they began equipping some of their Lambda probes with electronic heating, reducing their warm-up phase to about half a minute. The result was a further significant reduction in the toxic emissions produced by the cold engine.

The latest generation of planar probes needs only ten seconds to deliver reliable signals to the engine electronics. Bosch engineers are currently working on halving this extremely short time.

Almost 75% of probes produced today use planar technology. Bosch still also produces unheated probes. Spare parts remain available for every vehicle originally equipped with Bosch probes. In addition to the original parts, most cars can be equipped with the award-winning universal probe.

Top quality from the inventors
Today, many modern cars have several Lambda probes. They are no longer just fitted directly in front of the catalytic converter, but also behind it to control filtering efficiency. Lambda probes are now even fitted in diesel engines. Their constant further development is a mark of our commitment to reduce exhaust emissions. Lambda probes make filtering rates of around 98% possible.

All car manufacturers rely on the inventors from Bosch for this essential element of exhaust emissions filtering, both for original equipment and spare parts. Since 1976, Bosch has produced more than 400 million Lambda probes. Its worldwide production has now reached 30 million a year, which is another reason to celebrate.