Coasting Downshift Control for Automatic Transmission
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Solution Overview
Problem
Conventional reengagement downshift control in automatic transmissions leads to excessive engagement hydraulic pressure of speed-change friction elements when the torque converter lockup state is released, causing torque drawing-in and pop-up phenomena during reengagement-downshifting, which deteriorates shift quality.
Innovation Solution
A coasting downshift control device that predicts the release of the torque converter lockup state during reengagement downshift and reduces the engagement hydraulic pressure of the first speed-change friction element to below the lockup-ON hydraulic pressure, maintaining it at a lower hydraulic pressure to match the transmitted torque, thereby preventing excessive pressure and improving shift quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the engagement hydraulic pressure of the first speed-change friction element is set to lockup-ON hydraulic pressure during reengagement downshift in coast lockup state, then the downshift can be executed with sufficient torque transmission capability, but when the lockup state is released, the engagement hydraulic pressure becomes excessively high compared to the transmitted torque, causing torque drawing-in and pop-up phenomena that deteriorate shift quality
Solution Approach 1:
The patent applies dynamics by making the engagement hydraulic pressure adaptive rather than fixed. The control device dynamically adjusts the engagement hydraulic pressure based on the actual lockup state (lockup-ON or lockup-OFF) detected during reengagement downshift. When lockup-OFF is detected, the system transitions from high lockup-ON pressure to lower lockup-OFF pressure, allowing the pressure to evolve with changing operating conditions and preventing excessive pressure after lockup release
Solution Approach 2:
The patent changes the parameter of engagement hydraulic pressure based on the lockup state. By detecting whether the lockup state is maintained or released during reengagement downshift, the system switches between two distinct pressure levels (lockup-ON hydraulic pressure and lockup-OFF hydraulic pressure). This parameter change ensures that the engagement pressure matches the actual torque transmission capability, preventing torque drawing-in and pop-up phenomena
2Use of energy by moving object
If the lockup state of the torque converter is maintained during reengagement downshift to improve fuel economy, then the engine speed can be held higher and fuel-cutoff time prolonged, but the lockup state may be released during the downshift process, causing transmitted torque to decrease and engagement hydraulic pressure to become excessively high
Solution Approach 1:
The patent employs feedback by continuously detecting the actual lockup state during reengagement downshift and using this information to control the engagement hydraulic pressure. The lockup state detection provides feedback to the control device, which then adjusts the pressure accordingly. This closed-loop feedback mechanism ensures that the system responds to actual operating conditions, maintaining fuel economy benefits when lockup is sustained while preventing shift quality deterioration when lockup is released
Solution Approach 2:
The patent applies preliminary action by preparing the engagement hydraulic pressure control in advance based on predicted lockup state changes. The system proactively adjusts pressure before torque transmission issues can occur, ensuring smooth transition when lockup release is anticipated during reengagement downshift
Data Source
AI summary
Under a specified condition where a torque converter is kept in a lockup state to prolong the fuel-cutoff time, because of vehicle coasting with an accelerator opening APO=0, a downshift command is generated and then an automatic transmission causes a reengagement downshift by a drop in a release-side clutch hydraulic pressure Poff and a rise in an engagement-side clutch hydraulic pressure Pon. During the reengagement downshift, the engagement-side clutch hydraulic pressure Pon is reduced from a high lockup-ON hydraulic pressure to a low lockup-OFF hydraulic pressure after the time when the lockup is predicted to be released, thus preventing a torque drawing-in tendency of transmission output torque, which may occur at the time of the beginning of the inertia phase, from increasing, and also reducing in the width of a subsequent change in vehicle deceleration G, and consequently enhancing the shift quality.