Lambda sensor

LAMBDA SENSOR

This is of the "planar" type and is fitted on the front section of the exhaust pipe. It informs the injection-ignition control unit about combustion (stoichiometric ratio).

The electronic control unit identifies the composition of the mixture (lean or fat) from the lambda sensor output voltage.

It adapts the amount of fuel injected to ensure an optimum composition of the mixture (λ = 1), to create the ideal conditions for treating the exhaust gases in the catalytic converter.

If the mixture is too fat (λ < 1), the amount of fuel must be reduced and if the mixture is too lean (λ > 1), the amount of fuel must be increased.

1. Connection cable
2. Protective sleeve
3. Planar sensor element
4. Ceramic support pipe
5. Sensor housing
6. Ceramic seal
7. Protection pipe

The lambda sensor works on the principle of an oxygen concentration cell with solid electrolyte. The measuring cell surfaces are coated with micro-porous layers of precious material.

1. Exhaust gas
2. Reference air passage
3. Heater
4. Lambda sensor voltage

The lambda sensor, placed in contact with the exhaust gas, generates an electric signal, the voltage of which depends on the concentration of oxygen in the gas.

This voltage is characterised by an abrupt change when the composition of the mixture departs from λ = 1.

Lambda sensor heating is controlled by the injection control unit proportionally with the temperature of the exhaust gas. This prevents thermal shocks to the ceramic body due to contact with the condensed water contained in the exhaust gas when the engine is cold

The measurement cell and the heater are integrated in the "planar" (stratified) ceramic element with the advantage of obtaining quick heating of the cell, so that closed loop control (λ = 1) is enabled within 10 seconds from starting the engine.

a. Fat mixture (lack of air)

b. Lean mixture (excess air)