Intermediate Gear Downshift for CAC Condensate Purging
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Solution Overview
Problem
Turbocharged engines face engine misfires due to condensate accumulation in the Charge Air Cooler (CAC), which can lead to corrosion and leaks, especially during downshifting, as existing methods to prevent condensate build-up are incomplete and may still result in misfires during rapid air mass flow increases.
Innovation Solution
Implementing a method for multiple gear downshifting in stages, where the transmission temporarily operates in an intermediate gear to control air mass flow and condensate purging from the CAC, thereby reducing the risk of engine misfire by slowing the condensate introduction into the engine.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If a direct multiple gear downshift is performed from higher gear to lower gear, then the vehicle response time is improved, but condensate accumulates in the CAC and is drawn into the engine at once, increasing the chance of engine misfire
Solution Approach 1:
The downshift process is segmented into multiple stages: first downshifting to an intermediate gear to allow condensate purging at moderate air mass flow, then downshifting to the final lower gear. This segmentation prevents sudden condensate ingestion while maintaining acceptable vehicle response time.
Solution Approach 2:
The intermediate gear downshift serves as a preliminary action that purges condensate from the CAC before the final downshift to the lower gear. This preliminary condensate removal prevents misfire during the subsequent full downshift.
2Reliability
If the transmission gear is held at an intermediate gear for a duration to purge condensate, then engine misfire is reduced, but the vehicle response time increases
Solution Approach 1:
The system performs a partial downshift to an intermediate gear rather than the full downshift to the target lower gear. This partial action is sufficient to purge condensate at moderate air mass flow, and the transmission is then quickly downshifted to the final gear, minimizing the time penalty while achieving misfire prevention.
3Quantity of substance
If condensate build-up is prevented by maintaining high air mass flow, then condensate accumulation is reduced, but the engine operates at higher air mass flow levels continuously, increasing fuel consumption
Solution Approach 1:
Instead of maintaining continuously high air mass flow, the system uses periodic high air mass flow during intermediate gear downshifts to purge condensate. During normal operation, the engine can operate at lower, more fuel-efficient air mass flow levels, reducing overall fuel consumption while still preventing condensate accumulation through periodic purging.
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 reduces engine misfires by purging condensate at a slower rate, ensuring that the CAC is cleansed before shifting to a lower gear, thus preventing the sudden increase in air mass flow that could cause engine misfires.
Implementation Method 1
Condensate may form in the CAC when the ambient air temperature decreases, or during humid or rainy weather conditions, where the intake air is cooled below the water dew point
Implementation Method 2
a transmission gear may be downshifted from a higher gear to an intermediate gear, and then to the requested lower gear. By holding the transmission gear at the intermediate gear for a duration, condensate may be blown off the CAC and into the engine at a slower rate
Data Source
AI summary
Methods and systems are provided for performing a multiple gear downshift of a transmission gear by transiently operating in an intermediate gear. In response to air mass flow not reaching a threshold for CAC self-cleansing for a set duration, the transmission gear may be downshifted from a higher gear to an intermediate gear, and then to a requested lower gear. Downshifting through an intermediate gear may also be controlled based on the gear shift request and maximum air mass flow levels for engine misfire.