312000538 - INTRODUCTION - EXHAUST EMISSION CONTROL SYSTEM - FOR VERSIONS WITH DPF

DESCRIPTION OF COMPONENTS

Catalytic converter

SpecificationsThe catalytic converter is a post-treatment device for oxidizing the CO, HC and particulate, converting 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.
OperationThe exhaust gases passing through the cells heat the catalyzer, 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.

Dpf system (diesel particulate filter)

This is a mechanical filter that "traps" the carbon particles (particulate) and the engine oil ashes in the exhaust gases in diesel engines.The action of the DPF makes it possible to keep carbon particle levels down by around 90% in line with Euro 4 and 5 regulations.
The operation of the DPF system is managed by the engine injection control unit by means of suitable strategies. In addition to the actual filter the DPF system comprises an exhaust gas temperature sensor and a differential pressure sensor.The differential pressure sensor measures the pressure of the exhaust gases downstream of the filter, by means of a special pipe, signalling the gradual accumulation of particulate to the control unit. The particulate accumulation process and the relative increase in the pressure of the exhaust gases inside the filter depends on the engine load, the weight of the vehicle and the engine capacity and power. Therefore the particulate needs to be removed on a regular basis, regenerating the filter following a procedure that makes use of multiple injections to increase the temperature of the exhaust gases (about 600°C) and burn the particulate. The regeneration procedure is controlled by the injection control unit which acts: on fuel metering (up to five fuel injections in the same engine cycle per cylinder) and on air control (E.G.R. and turbo pressure).The regeneration phase takes place over a few minutes and does not affect the continuity of the torque supplied by the engine in terms of normal operation.
1. Particulate filter (DPF)2. Exhaust gas pressure intake3. Exhaust gas temperature sensor4. Differential pressure sensor5. Exhaust pipe with flexible section

Relative pressure sensor

The exhaust gas relative pressure sensor fitted on diesel versions with particle filters (DPF) is installed in the engine compartment and connected to the pressure intake upstream of the particle filter by means of a pipe resistant to high temperatures.It continuously provides information for the engine management control unit on the pressure value upstream of the filter (a value closely connected to the filling state).The pressure information, compared with atmospheric pressure, is communicated to the engine management control unit which, by means of a specific algorhithm, recalculates it subtracting the fall in pressure at the silencer thereby obtaining the difference in pressure at the sides of the filter.The purified signal is used, together with the estimate of the volumetric flow rate of the gases at the filter intake, to calculate the filter blockage status index.This index is constantly compared with a safety level (value for the blocked filter) which, if exceeded, activates the diagnosis and the switching on of the injection warning light.The operation of the sensor is based on the variation in the resistance value of a piezoceramic element which, by means of an electronic amplification circuit and signal compensation, translates the pressure value operating on the sensitive element into a voltage value (0-5V).The relative pressure sensor measures the relative pressure (p4) before the particle filter and the ambient pressure (p amb).The sensor calculates the difference in pressure betwen the two values measured: pe = p4 - p amb .The pressure sensor piezoresistive element and the circuits adopted for the amplification of the signal and the compensation of the temperature are incorporated in a silicon chip.The pressure p4 acts on the rear of the silicon diaphragm which is resistant to corrosive agents.The reference pressure p amb operates on the active side of the silicon diaphragm.

The maximum permitted values for the correct operation of the sensor are given below:

  • maximum supply voltage: 16V
  • maximum relative pressure (p4max): 500 KPa
  • maximum difference in pressure (pemax): 400 KPa
  • temperature interval: between -40 and +130°C
1. 5V power supply2. earth3. signal

Exhaust gas temperature sensor

SpecificationsPull-up power supply: 5 V +/- 0.1%Pull-up resistance: 1000 Ohm +/- 0.1%Rated resistance at 0ºC: 200 OhmOperating range: between -30°C and +120°COperationThe exhaust gas temperature sensor on diesel versions with a particulate filter (DPF) is fitted immediately before the particulate filter. The sensor continuously provides timely temperature information to the engine management control unit and carries out the task of checking that the filter regeneration temperature is within the safety limits and such as to guarantee the complete combustion of the particulate.
1. Terminal protection2. Protective pipe3. Flange4. Thermocouple5. Rigid cable6. Securing ring nut7. Flexible cable8. Teflon pipeThe electrical opration of the sensor is always monitored/diagnosed whilst a diagnostic check on the consistency of the value measured compared with the other temperature sensors in the engine management system is only carried out during starting.The operation of the sensor is based on the variation of the value of a platinum resistance with thin film technology depending on the temperature (a variation with an almost linear law, curve A).Curve B illustrates the variation in voltage sent directly to the engine management control unit which, by means of a conversion map, translates the voltage value into temperature
The table below show the resistance values of the exhaust ga temperature sensor
Temperature (°C)Resistance (ohm)
-40170,2
-20185,6
0201,0
25220,1
50239,0
100276,4
150313,2
200349,5
250385,1
300420,2
400488,6
500554,6
600618,3
700679,7
800738,7
900795,4
1000849,7