Torque Converter Lockup Control via Feedforward Feedback Switching
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Solution Overview
Problem
The existing control methods for torque converters with lockup clutches face challenges in precision control of slip rotation speed during the transition from converter mode to lockup mode, leading to potential engine stalling and control performance issues due to the nonlinear capacity characteristics of the torque converter.
Innovation Solution
A lockup control device and method that employs a programmable controller to perform feedforward control, calculating a target engine rotation speed based on the engine's running state and torque converter capacity characteristics, and switches to feedback control when the engine rotation speed falls below a reference value or when specific conditions are met, ensuring precise control of the slip rotation speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If feedback control is performed in the nonlinear region of the torque converter capacity characteristic, then the slip rotation speed can be controlled, but control performance deteriorates and engine stalling may occur
Solution Approach 1:
The control range of the torque converter is segmented into a nonlinear region and a linear region based on the capacity characteristic. Feedback control is applied only in the linear region where control performance is stable, while the nonlinear region uses a different control strategy, thus avoiding engine stalling while maintaining control precision where applicable.
Solution Approach 2:
The control system dynamically switches between feedforward control and feedback control based on the operating conditions and the position within the capacity characteristic curve. This dynamic adjustment allows the system to maintain optimal control performance across different operating regions without causing engine stalling.
2Reliability
If the lockup clutch is immediately released to avoid engine stalling, then engine stalling is prevented, but a shock occurs
Solution Approach 1:
The control system anticipates potential engine stalling conditions by monitoring operating parameters and prepares compensatory actions in advance. When approaching critical conditions, the system gradually adjusts the lockup clutch engagement rather than immediate release, cushioning the transition to prevent both stalling and shock.
Solution Approach 2:
The system uses feedback control to continuously monitor engine operation and slip rotation speed, adjusting the lockup clutch control in real-time. This feedback mechanism allows the system to prevent engine stalling while smoothly modulating the clutch engagement to avoid shocks during control adjustments.
3Productivity
If feedforward control is used to increase lockup differential pressure, then the change-over to lockup mode is facilitated, but control precision deteriorates in the nonlinear region
Solution Approach 1:
The control process is segmented into two phases: an initial feedforward control phase that rapidly increases lockup differential pressure to facilitate quick transition to lockup mode, followed by a feedback control phase that takes over in the linear region to ensure precise slip rotation speed control, thus combining the advantages of both control strategies.
Solution Approach 2:
Feedforward control is used as a preliminary action to quickly establish the lockup differential pressure and initiate the transition to lockup mode. This preliminary action is followed by feedback control that refines and precisely controls the slip rotation speed, ensuring both rapid response and high precision.
Data Source
AI summary
A controller (5) controls the engaging force between a pump impeller (1a) connected to an engine (2) and a turbine runner (1b) connected to an automatic transmission (23). The controller (5) first performs feedforward control of the engaging force. The controller (5) determines a reference value and a target rotation speed based on the capacity characteristics of the torque converter (1), and if the rotation speed of the engine (2) becomes less than the reference value, performs feedback control of the engaging force so that the deviation between the target rotation speed and the rotation speed decreases. When a predetermined condition is satisfied, the controller (5) changes over from feedforward control to feedback control, even if the rotation speed of the engine (21) is not less than the reference value. As a result, the control precision of feedback control when performing a slip lock-up, is increased.