323000519 - INTRODUCTION - EXHAUST EMISSION CONTROL SYSTEM

DESCRIPTION OF COMPONENTS

Catalytic converter

The catalytic converter is a post-treatment device for oxidising the CO, HC and particulate by transforming them into carbon dioxide (CO2) and water vapour (H20).The catalytic converter consists of a ceramic, honeycomb structure (1) with cells impregnated with platinum (2), which catalyzes the oxidation reactions.The exhaust gases passing through the cells heat the catalyser, triggering the conversion of pollutants into inert compounds.The oxidising chemical reaction of the CO, HC and particulate is effective at temperatures of between 200 and 350°C.Actually, above 350°C the sulphur contained in the diesel fuel starts to oxidise, producing sulphur dioxide and sulphur trioxide.

LAMBDA SENSOR

The linear UEGO planar Lambda sensor is fitted on the catalytic converter and informs the engine management control unit of the combustion progress.The sensor is an oxygen sensor containing two comparative cells that make it possible to measure values of λ (ratio between the quantity of intake air and the theoretical quantity of air required for the complete combustion of the fuel injected) within a wide range from λ = 0.7 (rich mixture) to the proportion of air (λ= (lean mixture).It is used to compare the reading of the air flow meter with the one mapped in the control unit and, if necessary, to correct the fuel injection so as to be within the emission limits.The sensor works by comparing the concentration of oxygen in the reference cell, housed inside the sensor, with the combustion gas flowing inside the comparison cell next to the reference cell. Depending on the resulting imbalance, the engine management control unit regulates a current signal (lp) that rebalances the oxygen content in the comparison cell through an electrochemical action. The value of lp is proportional to the λ value measured according to the graph illustrated below.
In order to activate the operation of the sensor quickly, the sensor contains a heater operated in duty cycle by the engine management control unit according to a calibrated strategy.The two comparison cells and the heater are incorporated in the same planar ceramic element (layers of several ceramic elements) in order to keep the structure compact and to guarantee high response and heating speeds for the actual element.
1. Connection lead2. Protective sleeve3. Flat sensor element4. Ceramic support pipe5. Sensor seat6. Ceramic seal7, Protective pipe

ELECTRICAL SPECIFICATIONS:

  • Max 7.5 V heater power supply from control unit
  • Heater resistance 3.2 ± 0.8 Ω
Pin out1. Pumping current (lp)2. Virtual mass3. Heater (-)4. Heater (+)5. Calibration current6. Nerst voltage