EGR CONTROL [SKYACTIV-D 1.8]
id0140s1161400
Outline
• To recirculate an optimum amount of exhaust gas to the combustion chamber according to engine operation conditions, the PCM performs duty control on the HP-EGR control valve and LP-EGR control valve to open and close the valves.
• During EGR control, the temperature of the intake gas is increased by the recirculated exhaust gas which affects the combustion temperature. To maintain the intake gas at the appropriate temperature, the opening angle of the HP-EGR control valve and LP-EGR control valve is controlled according to the driving environment/engine conditions.
• During diesel particulate filter regeneration control, the HP-EGR control valve is controlled so that it does not operate to prevent the post-injected fuel from circulating to the intake side.
• During DENOx/DESOx control, the exhaust gas is recirculated and the intake air is controlled to create a rich combustion condition (λ<1).
Block Diagram
Operation
• Based on the input signal, the PCM calculates the EGR amount to achieve the intake air amount and oxygen concentration.
• The HP-EGR control valve and the LP-EGR control valve are duty-controlled to open/close so that the EGR amount follows the targeted amount.
Target oxygen concentration
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― Calculated by adding corrections to the basic target oxygen concentration which is calculated based on the engine speed and fuel injection amount.
Target EGR amount
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― Calculated from target intake air oxygen concentration, exhaust gas oxygen concentration, and charging efficiency.
Actual EGR amount
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― Calculated from the MAF sensor/HP-EGR control valve/charging efficiency.
Valve open/close operation overview during vehicle travel
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• The PCM controls each valve as follows while the vehicle is driven under normal ambient temperature and stable driving conditions with engine warmed up completely*1.
*1 :The valve open/close condition varies depending on the engine operation conditions.
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• If the ambient and engine coolant temperatures are low, an increase correction in the EGR amount of the HP-EGR system (HP-EGR control valve and intake shutter valve) is made, and a decrease correction in the EGR amount of the LP-EGR system (LP-EGR control valve and exhaust shutter valve) is made to increase the intake manifold intake air temperature (IAT sensor No.2).
Operation during DPF regeneration
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• The PCM controls the LP-EGR control valve and intake shutter valve duty ratios according to the DPF regeneration conditions.
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― Intake shutter valve: Duty control
― HP-EGR control valve: Maintained at fully closed
― LP-EGR control valve: Duty control
― Exhaust shutter valve: Maintained at fully open
Operation during DENOx/DESOx control [European specs.]
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• The PCM controls the EGR amount by performing duty control for each valve according to the combustion condition to create a rich combustion condition (λ<1).
