=D R A F T (in progress - incomplete!) - Wideband zirconia sensor= edit
A variation on the zirconia sensor, called a "wideband" sensor, was introduced by Robert Bosch in 1994 (citation needed - what about NKG/Honda's development?), and has been used[1] to meet the ever-increasing demands for better fuel economy, lower emissions and better engine performance. It is based on a planar zirconia element which incorporates three electricalmechanical components in close physical proximity:
- Oxygen ion pump cell controlled by pump current (Ip).
- Narrowband like sense cell producing a Nernst voltage (Vs)
- Heating element to create a molten ion carrying environment.
A wideband sensor does not produce a simple voltage that can be measured and interpreted in the same way a narrowband sensor is used. Rather, circuitry and firmware within an external controller containing a feedback loop controls the ion pump current. The controller's strategy is to vary the pump current in order to keep the Nernst cell constant (typically at 450 mV). For lean mixtures the pump current transports oxygen away from the monitoring chamber. For rich mixtures oxygen is pumped into the chamber where it combines catalytically with unburnt hydrocarbons.
Other logic precisely controls the sensor's internal temperature by measuring the impedance of either the pump cell, the Nernst cell, or even the heater. The pump current is a measure of how many oxygen ions must be pumped into or out of the measuring chamber, and is thus an indication of the oxygen content of the exhaust gas that can be expressed in lambda units (where Lambda = 1.0 represent a stoichiometric mixture).
When a wideband controller is part of an ECU, the pump current measurement is often used directly as a digital signal with perhaps just some time averaging filtering. Aftermarket controllers will often incorporate a display and/or provide a voltage output that is linearised against Lambda (or perhaps percent oxygen) depending on the application.
The connector for a wideband sensor typically has six or seven active wires:
- Nernst cell output - (Vs)
- pump cell - (Ip)
- common for Vs & Ip circuits - (Vs/Ip)
- resistive heating element (two wires) - H+, H-
- calibration resistor (one if commoned with Ip, or two)
This sensor eliminates (of course it doesn't - the ECU does this) the lean-rich cycling inherent in narrow-band sensors, allowing the control unit to adjust the fuel delivery and ignition timing of the engine much more rapidly. In the automotive industry this sensor is also called a UEGO (for Universal Exhaust Gas Oxygen) sensor. UEGO sensors are also commonly used in aftermarket dyno tuning and high-performance driver air-fuel display equipment. The wideband zirconia sensor is used in stratified fuel injection systems, and can now also be used in diesel engines to satisfy the upcoming EURO and ULEV emission limits.