Hybrid Engine Stop Control for NOx Trap Saturation Avoidance
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Solution Overview
Problem
In hybrid vehicles, the frequent shifting of air-fuel ratios to manage NOx absorption in NOx trap catalysts leads to deteriorated fuel economy and exhaust performance, particularly after engine restarts when the NOx adsorption ratio exceeds the adsorption limit.
Innovation Solution
The internal combustion engine is controlled to stop when the NOx adsorption ratio is high, allowing for NOx removal during restart, thereby reducing the need for air-fuel ratio shifting and maintaining optimal lean operation, which suppresses fuel economy and exhaust performance deterioration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the internal combustion engine is stopped based on operation necessary determination when the NOx adsorption amount is close to the adsorption limit, then the engine can be stopped to save fuel, but the NOx adsorption amount exceeds the adsorption limit soon after restart, requiring immediate air-fuel ratio shifting to rich condition
Solution Approach 1:
The control device stops the internal combustion engine in advance when the NOx adsorption amount reaches a predetermined threshold before the adsorption limit. This preliminary action prevents the NOx trap catalyst from becoming saturated, thereby avoiding the need for immediate air-fuel ratio shifting to rich condition after engine restart, which would otherwise be required to desorb excess NOx.
Solution Approach 2:
The control device continuously monitors the NOx adsorption amount of the NOx trap catalyst and uses this feedback information to make real-time decisions about engine operation. When the adsorption amount reaches the predetermined threshold, the control device proactively stops the engine to prevent saturation, creating a closed-loop control system that maintains optimal exhaust performance while improving fuel economy.
2Reliability
If the exhaust air-fuel ratio is made rich to carry out desorption-reduction purification of absorbed NOx, then the NOx can be removed from the catalyst, but fuel economy deteriorates due to the rich operation
Solution Approach 1:
The control device performs preliminary engine shutdown before the NOx trap catalyst becomes saturated with NOx. By stopping the engine when the adsorption amount reaches a predetermined threshold, the system prevents the need for subsequent rich operation that would be required to desorb excess NOx, thereby avoiding fuel economy deterioration while still maintaining exhaust performance.
Solution Approach 2:
The control device converts the potential harm of NOx saturation into a benefit by using the NOx adsorption state as a trigger for engine shutdown. Instead of allowing the catalyst to become saturated and then requiring fuel-consuming rich operation to clean it, the system proactively shuts down the engine to prevent saturation, turning the NOx accumulation process into a useful indicator for fuel-efficient operation.
3Reliability
If air-fuel shifting is carried out frequently to manage NOx absorption and desorption, then the NOx can be controlled in the catalyst, but both fuel economy and exhaust performance deteriorate
Solution Approach 1:
The control device implements preliminary engine shutdown when the NOx adsorption amount reaches a predetermined threshold. This proactive measure prevents the need for frequent air-fuel ratio shifting cycles, as the engine is stopped before saturation occurs, thereby reducing the frequency of transitions between lean and rich operations and improving both fuel economy and exhaust performance consistency.
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
This approach prevents NOx adsorption ratio from reaching the limit, reducing the frequency of air-fuel ratio shifts, thus enhancing fuel economy and exhaust performance by allowing NOx removal during engine operation at a lean air-fuel ratio without shifting to a richer ratio.
Implementation Method 1
a NOx trap catalyst which absorbs NOx in exhaust gas when an exhaust air-fuel ratio is lean
Implementation Method 2
carries out the desorption-reduction purification of the absorbed NOx
Data Source
AI summary
A vehicle (1) is a hybrid vehicle including a traveling mode to travel only with the driving force of a drive motor (5). Vehicle (1) is mounted with an internal combustion engine (10) capable of being operated at an air-fuel ratio leaner than the theoretical air-fuel ratio. The operation of internal combustion engine (10) is controlled by a control unit (41). Control unit (41) is configured to determine whether to stop internal combustion engine (10) in an operation state, in consideration of the NOx adsorption ratio of a downstream-side exhaust purification catalyst (33) provided in an exhaust passage (31) of internal combustion engine (10).