3308472 - 1080B exhaust emission control system (Automatic transmission)
LAMBDA SENSOR
Of the "planar" type, it is mounted
on the front section of the exhaust pipe, and it informs the control
unit about the combustion trend (stoichiometric ratio).The electronic control unit identifies the
composition of the mixture (rich or lean) from the Lambda sensor
output voltage.It adjusts the quantity of fuel injected
to ensure the optimum composition of the mixture (l = 1) to create
the ideal conditions for the treatment of the exhaust gases in the
catalytic converter.If the mixture is too rich (l < 1), then
the quantity of fuel injected should be reduced and, if the mixture
is too lean (l > 1), then the quantity of fuel should be increased.a, Rich mixture (too little air)b, Weak mixture (too much air)The Lambda sensor, placed in contact with
the exhaust gases, generates an electrical signal whose voltage
depends on the concentration of oxygen present in the gases.This voltage undergoes a sudden change when
the composition of the mixture moves away from l = 1.The heating of the Lambda sensor is managed
by the fuel injection control unit in relation to the exhaust gas
temperature.This avoids thermal shocks on the ceramic
casing due to the contact with condensed water, present in the exhaust
gases when the engine is cold.The measuring cell and heater are built
into the "planar" (stratified) ceramic element, with the
advantage of obtaining quick heating of the cell, thus permitting
a closed loop" check (Lambda = 1) within 10 seconds of engine
start-up.
1, Connecting cable
2, Protective sleeve
3, Planar sensor element
4, Ceramic tube casing
5, Sensor housing
6, Ceramic seal
7, Protective tube
The operation of the Lambda sensor is based
on the principle of an oxygen concentration cell with solid electrolyte.The surfaces of the measuring cell are coated
with microporous layers of noble material.
1, Exhaust gases
2, Passage of reference air
3, Heater
4, Lambda sensor voltage
Specifications
Supply: 12 VInternal resistance: 0.5-1 kOhmCATALYTIC CONVERTER
The three-way catalytic converter
simultaneously reduces the three polluting gases present in the
exhaust gases:
- unburnt hydrocarbons (HC);
- carbon monoxide (CO);
- nitrogen oxides (NOx).
Two types of chemical reactions take
place in the converter:
- oxidation of the CO and HC, converted into carbon dioxide
(CO2) and water (H2O)
- reduction of the NOx converted into nitrogen (N2).
The converter consists of a monolith, a
metal mesh support for damping impacts and vibrations and an outer
stainless steel housing resistent to high temperatures and atmospheric
agents.The monolith consists of a honeycomb structure
comprising a ceramic material coated with a very thin layer of catalytically active
substances, platinum or rodium. These accelerate the chemical decomposition
of the harmful substances contained in the exhaust gases which,
passing through the core cells at temperatures of over 300°-350° C,
activate the catalyzers, thus starting the oxidoreduction reactions.To optimze the efficiency and duration of
the catalyzer, a perforated plate metal cone improves the diffusion
of the exhaust gases in the cells of the ceramic core.
1, Ceramic monolith
2, Metal support
3, Outer casing
4, Perforated plate metal cone
 | The noble metals contained in
the catalytic converter, because of the high temperature, are chemically
attacked if lead is present. |
For this reason the use of petrols containing
lead should be avoided, otherwise the converter will be quickly
and irreversibly damaged.Never use petrol containing lead, not even
in an emergency or for a very short time.
