Engine Control Device Managing SCR Temperature During Mode Switching
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Solution Overview
Problem
The NOx purifying performance of a selective catalytic reduction-type catalyst (SCR) declines due to ammonia (NH3) oxidation at high temperatures, which occurs when switching from stoichiometric to lean operation modes in internal combustion engines, leading to inadequate NH3 adsorption restoration.
Innovation Solution
A control device for internal combustion engines that includes a selective catalytic reduction-type catalyst, a NOx storage-reduction catalyst, and an EGR apparatus, which executes a rich spike and transient control to manage the EGR rate and air-fuel ratio, suppressing NH3 oxidation by increasing the EGR rate and making the air-fuel ratio richer in fuel during high SCR temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a rich spike is executed to restore NH3 adsorption amount of SCR during switching from stoichiometric operation to lean operation, then the NH3 adsorption amount can be restored, but NH3 oxidizes under high temperature environment exceeding upper limit temperature, leading to decline in NOx purifying performance
Solution Approach 1:
The control device detects SCR temperature in advance and determines whether to execute rich spike before NH3 oxidation occurs. When SCR temperature exceeds upper limit temperature, the control device suppresses rich spike execution to prevent NH3 oxidation, thereby maintaining NOx purifying performance while still allowing NH3 adsorption restoration when temperatures are appropriate.
Solution Approach 2:
The control device changes the operational parameters (air-fuel ratio, injection timing) based on SCR temperature conditions. When SCR temperature is within appropriate range, rich spike is executed to restore NH3 adsorption; when temperature exceeds upper limit, rich spike is suppressed to prevent oxidation, thus dynamically adjusting parameters to resolve the contradiction between NH3 adsorption restoration and NOx purifying performance maintenance.
2Quantity of substance
If rich spike is executed to supply reducing agent to NSR for NH3 generation, then NH3 can be generated and adsorbed by SCR, but during stoichiometric operation NH3 oxidizes at high temperature, causing inadequate NH3 adsorption restoration
Solution Approach 1:
The control device uses feedback from SCR temperature detection to determine whether to execute rich spike. The detected SCR temperature feeds back to the control logic, which decides whether the conditions are appropriate for rich spike execution. This feedback mechanism prevents NH3 oxidation loss by suppressing rich spike when SCR temperature exceeds upper limit, while still enabling NH3 generation and adsorption when temperatures are appropriate.
3Reliability
If EGR rate is increased during transient control to suppress NH3 oxidation, then NH3 adsorption is restored and NOx purifying performance is maintained, but fuel consumption may deteriorate
Solution Approach 1:
The control device executes transient control with increased EGR rate as a preliminary measure to suppress NH3 oxidation when SCR temperature exceeds upper limit temperature. By proactively increasing EGR rate before significant NH3 oxidation occurs, the system maintains NOx purifying performance and avoids the need for more fuel-intensive corrective actions later, thus resolving the contradiction between maintaining performance and managing fuel consumption.
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 effectively restores NH3 adsorption in the SCR, maintains NOx purifying performance, and prevents fuel consumption deterioration by controlling the EGR rate and air-fuel ratio during mode switching.
Implementation Method 1
An SCR has a function that adsorbs ammonia (NH3), and can selectively reduce NOx contained in exhaust gas by means of NH3
Implementation Method 2
The NSR stores NOx contained in exhaust gas under a lean atmosphere, and when a reducing agent such as HC or CO is supplied from upstream, the NSR releases the stored NOx to cause the NOx to react with the reducing agent
Implementation Method 3
the NSR releases the stored NOx to cause the NOx to react with the reducing agent to thereby reduce the NOx to NH3 and N2
Implementation Method 4
the NSR releases the stored NOx to cause the NOx to react with the reducing agent to thereby reduce the NOx to NH3 and N2
Implementation Method 5
an EGR (Exhaust Gas Recirculation) apparatus that causes EGR gas to recirculate from the exhaust passage to an intake passage
Implementation Method 6
An SCR has a function that adsorbs ammonia (NH3), and can selectively reduce NOx contained in exhaust gas by means of NH3
Data Source
AI summary
When switching an operation mode from a stoichiometric mode to a lean mode, a rich spike that supplies excessive fuel relative to a theoretical air-fuel ratio is executed. If the temperature of the SCR is greater than or equal to an upper limit temperature at a time of the switching, after execution of the rich spike, the switching to the lean mode is executed after executing transient control that makes the EGR rate higher than EGR rate in the lean mode and makes the in-cylinder air-fuel ratio an air-fuel ratio between the theoretical air-fuel ratio and the air-fuel ratio in the lean mode.