Automatic Transmission Downshift Thresholds for Stability
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional automatic manual transmissions face challenges in avoiding double downshifts and achieving precise gear selection via the accelerator pedal, leading to inefficient engine power utilization, increased consumption, and reduced comfort due to frequent gear changes and sensitivity requirements.
Innovation Solution
Designing downshift thresholds to run horizontally in a first range and have stepped sections in a second range of the accelerator pedal position, maintaining a constant accelerator pedal hysteresis, allowing for reproducible and precise gear selection and optimal engine power utilization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If conventional downshift maps with continuously increasing thresholds are used, then the transmission can respond to driver input, but the accelerator pedal hysteresis becomes too small requiring excessive driver sensitivity and causing frequent double downshifts
Solution Approach 1:
The downshift threshold map is segmented into multiple discrete threshold curves (e.g., T1, T2, T3, T4) corresponding to different gear transitions. Each threshold curve is defined by specific vehicle speed values at different accelerator pedal positions, creating distinct switching points rather than continuous thresholds. This segmentation provides stable, reproducible gear selection points that reduce double downshifts while maintaining driver controllability.
2Use of energy by moving object
If downshift thresholds are set to allow later downshifts for better engine power utilization, then consumption and comfort improve, but the driver must have very sensitive accelerator pedal metering which is difficult to achieve
Solution Approach 1:
The downshift thresholds are defined using specific vehicle speed values (parameters) that are optimized for each gear transition. By carefully selecting these speed thresholds at different accelerator pedal positions, the system achieves later downshifts that maximize engine power utilization in higher gears, improving consumption and comfort. The discrete parameter values provide clear switching points that do not require excessive driver sensitivity.
3Speed
If the accelerator pedal hysteresis is reduced for more responsive gear changes, then shift responsiveness improves, but double downshifts occur more frequently and driver sensitivity requirements increase
Solution Approach 1:
The control unit pre-calculates and stores multiple downshift threshold curves with optimized hysteresis characteristics before operation. These thresholds are determined in advance to provide appropriate hysteresis buffers that prevent double downshifts while maintaining responsive gear changes. The system does not need to dynamically adjust hysteresis during operation, as the preliminary threshold definitions already account for stable switching behavior.
Data Source
Figure 1
Figure 2
AI summary
The method involves defining upshifting and downshifting thresholds based on a function accelerator pedal position for each sequential gear change, and storing a limiting value valid for the respective upshifting and/or downshifting as vehicle speed value in a controller. Two of the downshifting thresholds are formed in an area of the accelerator pedal position in a horizontally running manner, and are formed in another area of the accelerator pedal position in a partial cascaded manner.