Automatic Transmission Controller Slip Ratio Adjustment
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Solution Overview
Problem
Existing automatic transmission systems with lockup clutches experience instability in feedback control due to varying automatic transmission fluid temperatures, leading to engine hunting and vehicle vibrations, as the friction modifier's activation affects the clutch's friction characteristics.
Innovation Solution
A controller that detects automatic transmission fluid temperature and adjusts target slip ratios for the lockup clutch, selecting from multiple pre-defined ratios based on temperature thresholds to maintain stable feedback control and optimize clutch engagement, thereby preventing abrupt changes in transmission torque.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the working range of the lockup clutch is expanded by setting a lower ATF temperature, then fuel economy is improved, but the friction modifier is less activated causing deteriorated friction characteristic and unstable feedback control
Solution Approach 1:
The patent applies parameter changes by switching the feedback gain according to ATF temperature. When temperature is low, a larger feedback gain is used to compensate for the deteriorated friction characteristic and ensure stable control. When temperature is high, a smaller feedback gain is sufficient. This dynamic adjustment of the feedback gain parameter resolves the contradiction between expanding the working range to low temperatures and maintaining control stability.
2Reliability
If feedback gain is switched according to ATF temperature, then control stability is improved, but the followability to target value is still insufficient
Solution Approach 1:
The patent applies dynamics by making the target slip ratio variable according to ATF temperature. Instead of using a fixed target slip ratio, the system selects different target values based on temperature conditions. This allows the control system to adapt to the changing friction characteristics at different temperatures, improving both stability and followability to the target value simultaneously.
3Ease of operation
If hydraulic pressure is applied to the lockup clutch at low ATF temperature, then clutch engagement is achieved, but abrupt change in transmission torque occurs due to inactive friction modifier
Solution Approach 1:
The patent applies preliminary action by pre-selecting an appropriate target slip ratio based on ATF temperature before engagement occurs. When temperature is low, the system预先 sets a larger target slip ratio to account for the inactive friction modifier. This preliminary adjustment prevents abrupt torque changes during engagement by anticipating the deteriorated friction characteristic and compensating for it in advance.
Data Source
AI summary
A controller for automatic transmission that performs feedback control on a slip ratio of a lockup clutch is adapted to select one target slip ratio from a plurality of target slip ratios based on a detected automatic transmission fluid temperature of a torque converter. Thus, the controller can ensure good followability to a target value of the feedback control even when the automatic transmission fluid temperature is low. The controller can effectively prevent engine hunting and the associated vibrations of vehicle body. Therefore, the controller can accomplish a favorable slip control of the lockup clutch even if an operating range of the lockup clutch is expanded to a range where the automatic transmission fluid temperature is low.