Oxygen Sensor Target Value Control for Exhaust Regeneration
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Solution Overview
Problem
Existing methods for controlling oxygen concentration in internal combustion engine exhaust systems, particularly during transitions from lean to rich combustion phases, face challenges such as hydrocarbon peak formation and sensor degradation due to abrupt air/fuel ratio changes and deposits on oxygen sensors, which impede sensor performance and increase emissions.
Innovation Solution
A computer-implemented method and device that modulate the oxygen sensor target value based on exhaust gas flow speed and air/fuel ratio, lowering the target value in a stepped phase and filtering it during regeneration, ensuring the sensor's reaction speed is maintained and hydrocarbon peaks are reduced.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a standard step target value adjustment is used for the oxygen sensor during transitions from lean to rich combustion phases, then the AFR target value changes quickly (e.g., from 1.5 to 0.95), but this causes the AFR to fall below the target value (as low as 0.9), resulting in increased hydrocarbon quantity and sensor probe soiling
Solution Approach 1:
The patent applies dynamics by making the oxygen sensor target value adaptive rather than fixed. The target value is dynamically adjusted based on the measured air/fuel ratio and a filter coefficient that depends on exhaust gas flow speed. This allows the system to respond quickly to changes in combustion phase while preventing the AFR from falling below the target value, thereby reducing hydrocarbon peaks and sensor soiling without sacrificing reaction speed.
Solution Approach 2:
The patent changes the parameter of the oxygen sensor target value from a constant step adjustment to a dynamically modified value. The target value is adjusted using a filter coefficient that is a function of exhaust gas flow speed, which in turn depends on engine speed and load. This parameter change allows the system to maintain appropriate AFR control during transitions while preventing harmful effects.
2Reliability
If proportional-integral (PI) control is used to act on the post-injection quantity in conjunction with the AFR target value, then the oxygen concentration is controlled, but the AFR falls below the target value during rich combustion phases, causing increased hydrocarbon quantity and sensor degradation
Solution Approach 1:
The patent enhances the PI control by introducing an additional feedback mechanism. The oxygen sensor target value is continuously adjusted based on the difference between the measured AFR and the target AFR, combined with a filter coefficient that responds to exhaust gas flow speed. This dual feedback approach ensures the AFR remains at or above the target value while maintaining reliable oxygen concentration control, preventing the precision loss that occurs with standard PI control alone.
3Productivity
If the oxygen sensor target value is lowered abruptly during regeneration, then the transition from lean to rich combustion phase is achieved, but the sensor performance slows down due to deposits of hydrocarbons and soot on the probe
Solution Approach 1:
The patent applies preliminary action by pre-adjusting the oxygen sensor target value using a filter coefficient before the actual regeneration process begins. The filter coefficient is calculated based on exhaust gas flow speed, which anticipates the conditions during regeneration. This preliminary adjustment prevents excessive hydrocarbon formation that would otherwise deposit on the sensor probe, thereby maintaining sensor performance and reaction speed throughout the regeneration process while still achieving efficient NOx reduction.
Data Source
AI summary
A method is disclosed for controlling a concentration of oxygen that is measured by an oxygen sensor of an after-treatment system of an internal combustion engine when a regeneration of an after-treatment device is required. The method may be a computer-implement method. An oxygen sensor target value is lowered in a stepped phase as a function of an exhaust gas flow speed as the exhaust gas passes through the after-treatment system. The oxygen sensor target value is lowered evenly as a function of the exhaust gas flow speed and by a filter phase when a measured air/fuel ratio value is less than or equal to an AFR threshold value and until the oxygen sensor target value is equal to an oxygen sensor final target value. The oxygen concentration is controlled by applying the oxygen sensor target value.