Automatic Transmission Lock-Up Control During Forced Downshift
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Solution Overview
Problem
Conventional automatic transmission control devices fail to suppress the unnatural feeling experienced by drivers when the accelerator foot is released during auto-upshift in a lock-up engaged state, leading to engine rotation blow-up and inadequate vehicle acceleration response.
Innovation Solution
Implementing a forced downshift control mechanism that starts before the engine rotation speed reaches the lock-up release rotation speed during auto-upshift, maintaining the lock-up clutch engaged to prevent unnatural driver feedback.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If lock-up clutch is released when engine rotation speed goes below lockup release rotation speed during auto-upshift, then shift control is achieved, but engine rotation blow-up occurs and vehicle acceleration response becomes inadequate
Solution Approach 1:
The control device performs preliminary detection of accelerator operation amount before the lock-up release rotation speed is reached. When a kick-down operation with relatively large accelerator return amount is detected, the control device executes shift delay processing in advance, preventing the lock-up clutch from being released and avoiding engine rotation blow-up before it occurs.
Solution Approach 2:
The control device applies preliminary anti-action by detecting the driver's acceleration intention through accelerator operation amount before the harmful effect (engine rotation blow-up) occurs. When kick-down operation is detected, the system preemptively delays the shift, counteracting the potential engine rotation instability before it can manifest.
2Speed
If shift delay processing is executed when kick down operation with large accelerator return amount is detected, then engine rotation blow-up is prevented, but shift response becomes delayed
Solution Approach 1:
The control device applies partial action by not delaying all shifts uniformly, but only those shifts that would occur during kick-down operations with relatively large accelerator return amount. This selective approach prevents engine rotation blow-up in critical cases while maintaining normal shift response in other situations.
Solution Approach 2:
The control device changes the shift control parameter dynamically based on accelerator operation amount. When kick-down operation is detected, the shift timing parameter is adjusted to delay the shift; otherwise, normal shift timing is maintained, optimizing both engine rotation stability and shift response time under different operating conditions.
3Reliability
If lock-up clutch is released during coast state by accelerator return operation, then shift control is achieved, but driver experiences unnatural feeling and acceleration response is inadequate
Solution Approach 1:
The control device uses feedback from accelerator operation amount detection to determine whether to delay shift. By monitoring the accelerator return amount, the system receives feedback about driver intention and adjusts shift timing accordingly, preventing unnatural driver feedback when kick-down operation is detected during coast state.
Data Source
AI summary
A control device for an automatic transmission arranged between an engine and a drive wheel, the automatic transmission including a torque converter having a lock-up clutch, and a transmission mechanism. The control device includes a shift control unit configured to perform shift control of the transmission mechanism. The shift control unit includes a forced downshift control processing unit configured to implement forced downshift when an accelerator foot release operation is performed during auto-upshift in a power-on state with the lock-up clutch engaged. The forced downshift control processing unit is configured to start the forced downshift before an engine rotation speed that has decreased due to the auto-upshift reaches a lock-up release rotation speed.