Automatic Transmission Downshift Control via Upshift Threshold Inversion
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Solution Overview
Problem
Existing automatic manual transmission systems, particularly during braking, experience complex control methods leading to 'pendulum shifts' that reduce driving comfort and increase control effort, as they often result in immediate upshifts during acceleration phases after braking.
Innovation Solution
The method involves detecting a braking process and using the zero accelerator pedal limit value of existing upshift thresholds as downshift thresholds, allowing for early engagement of the next lower gear during braking, thereby avoiding complex adaptations and pendulum shifts by 'virtually' converting upshift thresholds into downshift thresholds only for specific conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If complex adaptation methods are used to implement brake downshifts, then downshift control can be achieved, but control complexity and device complexity increase significantly
Solution Approach 1:
The patent inverts the conventional approach by using upshift threshold curves (defined for accelerator pedal positions) to determine downshift points during braking. Instead of creating separate complex downshift adaptation logic, the system reuses existing upshift threshold data structures by evaluating them at zero accelerator pedal position, thereby eliminating the need for separate downshift threshold definitions and reducing control complexity
Solution Approach 2:
The patent makes the upshift threshold characteristic curves serve multiple functions: they define both normal upshift points during acceleration and downshift points during braking. By evaluating the same upshift threshold curves at different accelerator pedal positions (including zero position during braking), the system achieves multi-functionality without requiring separate downshift control logic
2Reliability
If complex adaptation methods are used for downshift control, then downshift functionality is achieved, but control effort and computational requirements increase
Solution Approach 1:
The system uses its existing upshift threshold determination logic to serve the downshift function as well. The control unit already has the capability to evaluate upshift thresholds based on accelerator pedal position and vehicle speed; during braking, this same capability is applied by evaluating thresholds at zero accelerator pedal position, eliminating the need for separate downshift adaptation computations
Solution Approach 2:
The patent merges the upshift and downshift control logic into a single unified process. Both gear changes are determined by evaluating the same upshift threshold characteristic curves, with the distinction being the accelerator pedal position context. This consolidation eliminates redundant control algorithms and reduces overall control effort
3Productivity
If traditional downshift methods are used during braking, then gear changes occur, but pendulum shifts occur reducing driving comfort
Solution Approach 1:
The patent applies preliminary anti-action by detecting the braking state (zero accelerator pedal position) before executing the downshift. By evaluating upshift thresholds specifically at this condition and comparing current speed against these thresholds, the system proactively prevents the conditions that would lead to immediate post-braking upshifts, thereby avoiding pendulum shifts before they can occur
Solution Approach 2:
The patent applies local quality by treating the zero accelerator pedal position condition as a special case with specific evaluation rules. The upshift threshold curves are evaluated at this specific accelerator pedal position to determine downshift points, creating a localized control strategy for braking conditions that differs from normal acceleration conditions, thereby optimizing driving comfort during braking transitions
Data Source
Figure 1
AI summary
Method for implementing the gear changes of an automatic transmission of a vehicle, in particular of a dual clutch transmission, wherein for each possible sequential gear change, depending on the accelerator pedal position, an upshift threshold (HS) and/or a downshift threshold (RS) are each defined, specifically, the limiting value applicable to the respective up- or downshift being stored in a control device as a corresponding vehicle speed value, the changing vehicle speed and the changing accelerator pedal position during the vehicle's journey being measured and in a braking phase of the vehicle a downshift, in particular a braking downshift, being implemented. The driving comfort is increased by the fact that a braking process of the vehicle is first detected, namely an activation of the brake pedal is sensed, that a check takes place of whether the accelerator pedal is inactivated and that for the case where the brake pedal is activated and the accelerator pedal inactivated, the current vehicle speed (V3) is determined and compared with the respective lower limit value of the next lower upshift threshold (HS), namely with the zero-accelerator-pedal limit value (NF) of this upshift threshold (HS), and that then, if this zero-accelerator-pedal limit value (NF) or a specific difference value (DNF), calculated in relation to this zero accelerator-pedal limit value (NF), has not been reached, then the lower gear in the transmission defined by the thereby unattained upshift threshold (HS) is engaged.