Automatic Transmission Control for Urban Speed Limits
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Solution Overview
Problem
Vehicles with non-powershift-capable transmissions, such as the BMW i8, face tractive power interruptions and reduced electric driving performance due to gear shifting limitations, leading to a poorer driving experience and decreased acceleration capabilities, especially in urban environments where lower gears provide better torque and faster acceleration.
Innovation Solution
A control method and device that utilize driving-speed-related data from navigation systems and other digital sources to forecast speed limit regions, allowing the transmission to maintain or shift into lower gears when approaching urban speed limits, ensuring optimal gear usage based on driver power requests and speed thresholds, thereby enhancing comfort and acceleration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the vehicle starts driving in second gear to avoid frequent combustion engine startup, then the combustion engine startup frequency is reduced, but the wheel torque and acceleration capability are decreased
Solution Approach 1:
The control device receives data about upcoming speed limit regions in advance and proactively maintains the vehicle in first gear before entering the region, ensuring optimal torque availability is preserved while avoiding unnecessary combustion engine startups. This preliminary action allows the system to prepare for upcoming conditions rather than reacting to them.
Solution Approach 2:
The transmission gear selection is made dynamic and adaptive based on real-time conditions including upcoming speed limit regions, current vehicle speed, and driver power requests. The system continuously adjusts gear selection between first and second gear based on forecasted driving conditions, optimizing both energy efficiency and torque availability.
2Speed
If the vehicle shifts to second gear at higher speeds, then the vehicle can achieve higher speeds, but the acceleration capability from standing position is reduced
Solution Approach 1:
The system receives advance data about upcoming speed limit regions and proactively maintains first gear selection before the vehicle needs to accelerate, ensuring full power and acceleration capability are available when needed. This preliminary gear selection strategy prevents power loss that would occur if the vehicle were already in second gear.
Solution Approach 2:
The control device dynamically changes the transmission gear parameter based on multiple factors including current speed, upcoming speed limit regions, and driver power requests. The system optimizes the gear selection parameter to balance speed achievement and acceleration capability by selecting first gear when acceleration is needed and second gear when speed maintenance is sufficient.
3Force
If the vehicle maintains first gear in urban environments with speed limits, then the wheel torque and acceleration are improved, but the transmission must be non-powershift-capable which causes tractive power interruptions during shifting
Solution Approach 1:
The control device receives advance data about upcoming speed limit regions and proactively maintains first gear selection before the vehicle needs to shift, avoiding unnecessary gear changes that would cause tractive power interruptions. This preliminary action eliminates the harmful effect of power interruptions by preventing unnecessary shifting events.
Solution Approach 2:
The system continuously monitors vehicle speed, driver power requests, and upcoming speed limit regions to provide feedback for optimal gear selection. This feedback mechanism ensures gear changes only occur when necessary and appropriate, minimizing tractive power interruptions while maintaining optimal wheel torque in urban environments.
Data Source
AI summary
In a control method and a control device for shifting an automatic and, in particular, non-powershift-capable transmission having at least two gears, data of a driving-speed-related data source are received by at least one electronic control unit for a defined forecast range. The data are such that the control unit can determine therefrom a region at least lying in the forecast range and having a limit speed below the maximum speed of the lower gear. If such a region was actually detected in the forecast range, either the lower gear is maintained or shifting is performed from the higher gear to the lower gear. Shifting back to the lower gear is preferably performed only if a driver power request value lies below a defined threshold and the driving speed lies below the maximum speed of the lower gear.