Press Release Summary = For many years manufacturers sought a method to extend the range of exhaust gas sensors to cover the entire range of engine operations. In the early 1990\'s NTK patented the pump-cell sensor now known as WBO2 or UEGO sensor.
Press Release Body = For many years manufacturers sought a method to extend the range of exhaust gas sensors to cover the entire range of engine operations. In the early 1990\'s NTK patented the pump-cell sensor now known as WBO2 or UEGO sensor. The first ones (NTK L1H1) were used on lean-burn Honda engines because engine operation could not be controlled by a NBO2 signal on the lean side of 14.7 (see curve). It was quickly discovered that these sensors also work in a rich gas environment. Many modern turbo engines require tight control over the air/fuel ratio to keep emissions at minimum but nevertheless produce enough power. These applications keep the engines just shy of the onset of knock. The Bosch LSU4 series sensors were designed with that application in mind and are widely used by OEM\'s in turbo engines.
WBO2 sensors combine a regular NBO2 sensor and what\'s called a pump cell in one package. The pump cell is kind of the opposite of a NBO2 sensor. It can pump oxygen ions in or out of the sensor cavity. An electrical current through the pump cell transports the oxygen ions. If the current flows in one direction, oxygen ions are transported from the outside air into the sensor, in the other direction oxygen ions are transported out of the sensor to the outside air. The magnitude of the current determines how many oxygen ions/second are transported, just like the electrical current through a fuel pump determines the fuel transport rate.
Both, the NBO2 part and the pump cell, are mounted in a very small measurement chamber open with an orifice to the exhaust gas. The pumping rate of the pump cell is very temperature dependent. Therefore the sensor head temperature must be tightly regulated through a built in heater. A WBO2 controller (like the LM-1) monitors and regulates the heater to keep it at a constant temperature. In a rich condition the WBO2 controller regulates the pump cell current such that just enough oxygen ions are pumped into the chamber to consume all oxidizable combustion products. This basically produces a stochiometric condition in the measurement chamber. In that condition the NBO2 sensor part produces 0.45V. In a lean condition the controller reverses the pump current so that all oxygen ions are pumped out of the measurement chamber and a stochiometric condition again exists there. The pump cell is strong enough to pump all oxygen out of the measurement chamber even if it was filled with free air.
The task of the WB controller is then to regulate the pump current such that there is never any oxygen nor oxidizable combustion products in the measurement chamber. The required pump current is then a measure for the Air/Fuel ratio.
This is how analog WB meters work. They are called analog because the input/output signals of the controller are smoothly varying voltages/currents. The PID controller can be implemented in a microprocessor or as analog electronic circuit using amplifiers, transistors and so on. Implementing it in a microcontroller does not make it a digital system. The LM-1 operates the WBO2 sensor differently. Its (pat. pend.) working principle will be explained in a future release.
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2022
