2888232 - 1080B exhaust emission control system

LAMBDA SENSOR

Specifications

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 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 is characterized by a sudden change when the composition of the mixture moves away from Lambda = 1.

Composition

The sensitive part of the sensor consists of a ceramic casing (1), with a zirconium dioxide base, covered in a layer of platinum, closed at one end, inserted in a protective pipe (2) and housed in a metal casing (3).The outer part (b) of the ceramic casing is exposed to the current of exhaust gases, whilst the inner part (a) is in contact with the ambient air.The operation of the sensor is based on the fact that, at temperatures above 300°C, the ceramic material becomes a conductor of oxygen ions. As a result, according to the percentage difference in the quantity of oxygen at the sides (a, b) of the ceramic casing, a tension is produced between the two edges which is an indication of the difference in oxygen between the two environments. When the sensor provides a low voltage level (below 200 mV), the control unit recognizes that the mixture istrength is lean (Lambda > 1) and increases the quantity of fuel injected. When the sensor provides a high voltage level (above 800 mV), the control unit recognizes that the mixture is rich (Lambda < 1) and decreases the quantity of fuel injected. The Lambda sensor varies the injection times so that the engine is operating with a Lambda coefficient continuously oscillating between around 0.980 and 1.020.The Lambda sensor is operational at when the temperature of the ceramic casing is 300°C; at lower temperatures the signal is not reliable and the injection control unit does not carry out the adjustment in closed-loop until the sensor warms up.To ensure that the operating temperature is reached rapidly, the sensor is fitted with an internal heating resistance supplied by a special relay.a, Electrode (+) in contact with the outside air b, Electrode (-) in contact with the exhaust gases 1, Ceramic body 2, Protective tube 3, Metal body 4, Electrical resistorElectrical specifications:Heater supply: 12 VHeating resistance: 43 - 4.7 ohm.

CATAYTLIC 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 petrol containing lead should be avoided or else the converter will be rapidly and irreversably damaged. Never use petrol containing lead, not even in an emergency or for a very short time.