LSU Wideband Lambda Probes in Front of the Catalytic Converters

2469 - LSU Wideband Lambda Probes in Front of the Catalytic Converters

In order to ensure compliance with exhaust emission standards EU4 and TIER 2 (FED), the Boxster and Boxster S are equipped with an LSU wideband Lambda probe in front of the pre-catalytic converters for each cylinder bank. In contrast to the step Lambda probe, which merely indicates whether the engine mixture is lean or rich, the continuously measuring wideband Lambda probe assesses precisely how lean or rich the mixture is. This additional information enables the mixture to be adjusted such as to ensure that the catalytic converter operates effectively. This is also possible when highly dynamic load changes apply. Vehicles equipped with this wideband Lambda probe run with Lambda control shortly after cold starting, from idling up to full throttle. The LSU wideband Lambda probe represents a further development of the LSF Lambda probe.

Advantages of the LSU Wideband Lambda probe:
- Exact measurements from Lambda > 0.7 (rich mixture) to Lambda < 4 (pure air) are possible
- The LSU probe supplies a continuous signal, which is evaluated in the Motronic control unit
- Controlled operation with Lambda control is possible under all conditions
- The wideband Lambda probe is ready for use very quickly
- The Lambda control circuit responds faster to a change in the mixture
- Improved regulating action with increased dynamism

Design of the LSU broadband Lambda probe:
- The LSU consists of different planar functional layers
- The actual sensor element of the broadband Lambda probe consists of a combination of a Nernst concentration cell (1) and a pump cell (2) transporting oxygen ions
- The broadband Lambda probe requires a special operating electronics system (6) in the form of an evaluation circuit in the Motronic control unit.
- The evaluation circuit contains the control electronics for the pump cell and the sensor cell to generate the sensor signal
- The control current of the electronic pump cell always generates Lambda 1 in the measuring cell (3)
- This is continuously monitored via the voltage of the sensor cell (450 mV).
- The evaluation circuit calculates the precise Lambda value of the exhaust gas on the basis of the deviation of the pump cell current (0 mA ± 1 mA).
- LSU temperature control is also integrated in the evaluation circuit.