Lean NOx Trap Regeneration Torque Control
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Solution Overview
Problem
Lean NOx traps in internal combustion engines require periodic rich exhaust gas regeneration, which causes torque disturbances during rich operation, and existing systems increase hydrocarbon emissions while reducing NOx levels.
Innovation Solution
A control system and method that adjusts airflow and fuel output based on actual and desired air-fuel ratios, using an air control module and fuel control module to manage airflow and fuel delivery, including feedforward and feedback loops to minimize torque disturbances and optimize NOx trap regeneration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If periodic rich exhaust gas regeneration is performed to reduce NOx levels, then NOx emissions are reduced, but torque disturbances occur during rich operation
Solution Approach 1:
The control system performs preliminary actions by adjusting the air-fuel ratio trajectory before regeneration is needed, and by pre-positioning the lambda trajectory (λtraj) to prepare for smooth transition. The delay module retains λtraj for an initial period to compensate for time lags, ensuring the system is ready for regeneration without sudden torque disturbances.
Solution Approach 2:
The system dynamically adjusts the air-fuel ratio by implementing a trajectory-based control approach. The lambda trajectory (λtraj) is continuously updated based on current lambda (λ) and desired lambda (λdes), allowing smooth transitions between lean and rich operations. The air control module dynamically modifies airflow using feedforward and feedback mechanisms to maintain torque stability during dynamic regeneration cycles.
2Ease of operation
If air-fuel ratio is controlled to enable smooth transitions between lean and rich operations, then torque disturbances are minimized, but system complexity increases
Solution Approach 1:
The controller integrates multiple functions into a single control unit that handles air-fuel ratio management, lambda trajectory generation, delay compensation, and regeneration control. The air control module combines feedforward and feedback mechanisms in one system, reducing the need for separate dedicated components while achieving smooth transitions and torque stability.
Solution Approach 2:
The control system implements feedback loops where the actual air-fuel ratio (λ) is continuously monitored and compared with the desired trajectory (λtraj). The fuel feedback module determines delta fuel quantity based on the difference between λ and λtraj, and the air feedback module adjusts EGR and throttle based on airflow errors. This feedback mechanism enables smooth transitions without requiring overly complex open-loop control systems.
3Ease of operation
If lambda trajectory is adjusted in real-time with delay compensation, then transition smoothness is improved, but computational requirements increase
Solution Approach 1:
The delay module pre-compensates for computational lags by retaining λtraj for an initial period of time. This preliminary action accounts for the time required to supply fuel feedforward to the engine and communicate with the lambda sensor, ensuring that the trajectory adjustments are already prepared when needed, reducing real-time computational burden.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system effectively controls torque output and reduces NOx emissions by smoothly transitioning between lean and rich air-fuel operations, minimizing torque disturbances and hydrocarbon emissions during regeneration.
Implementation Method 1
The NOx storage catalysts absorb and decompose the NOx with combustible gases such as carbon monoxide (CO) or hydrocarbon (HC)
Implementation Method 2
The NOx storage catalysts absorb and decompose the NOx with combustible gases
Implementation Method 3
The engine controls the air-fuel mixture to achieve an ideal air-fuel mixture ratio (stoichiometric ratio). At the optimum stoichiometric ratio, all of the fuel is burned using all of the oxygen in the air
Data Source
AI summary
A control system and method for controlling torque output of an engine include an air control module that receives an actual airflow and a desired airflow and outputs an adjusted actual airflow based on the actual airflow and the desired airflow. A fuel control module receives the adjusted actual airflow and controls fuel output based on the adjusted actual airflow, a ratio (λ) of an operating air-fuel mixture to an ideal air-fuel mixture, and an operating curve (λtraj).