CVT Control Device Same-Pressure Upshift Strategy
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Solution Overview
Problem
The existing control systems for belt-type continuously variable transmissions experience shift shocks during upshifts due to fluctuations in line and secondary pressures, leading to inefficiencies in fuel economy and drivability.
Innovation Solution
A control device that includes a secondary-pressure control mechanism using feedback control with integral action to maintain a same-pressure state between line and secondary pressures, and a restriction mechanism to limit integral term accumulation, ensuring the line pressure is reduced to its minimum necessary level during upshifts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If feedback control is used to maintain same-pressure state between line and secondary pressures, then fuel economy is improved by minimizing line pressure, but shift shocks occur during upshifts due to pressure fluctuations
Solution Approach 1:
The control device predicts the secondary pressure during upshift based on the relationship between line pressure and secondary pressure, and adjusts the secondary pressure in advance before the actual upshift occurs. This preliminary adjustment prevents pressure fluctuations and shift shocks while maintaining minimal line pressure for fuel economy.
Solution Approach 2:
The control device uses feedback control to maintain the same-pressure state between line and secondary pressures during normal operation, improving fuel economy. During upshift, it switches to predictive control that uses the established pressure relationship to anticipate and counteract pressure fluctuations, eliminating shift shocks.
2Use of energy by moving object
If line pressure is reduced to minimum necessary level, then fuel economy is improved, but belt clamping force may become insufficient
Solution Approach 1:
The control device dynamically adjusts the secondary pressure based on the predicted upshift conditions and the established relationship between line and secondary pressures. This maintains adequate belt clamping force during critical operations while allowing line pressure to remain at minimum levels for fuel economy improvement.
3Reliability
If integral term accumulation is restricted during same-pressure control, then shift shocks are reduced, but pressure control precision may deteriorate
Solution Approach 1:
The control device dynamically adjusts the integral term accumulation restriction based on the operational phase. During upshift prediction and execution, it restricts integral accumulation to prevent shift shocks. During normal steady-state operation, it relaxes the restriction to maintain precise pressure control, thus achieving both goals.
Data Source
AI summary
A CVTECU includes a secondary-pressure control section and a line-pressure control section that performs a same-pressure control to equalize a line pressure and a secondary pressure with each other if a predetermined start condition is satisfied. The line-pressure control section realizes a same-pressure state between the line pressure and the secondary pressure by lowering the line pressure below a target secondary pressure, and then controls the line pressure such that an actual secondary pressure is brought to the target secondary pressure by hydraulic feedback control while maintaining the same-pressure state. The secondary-pressure control section includes a restriction section that restricts an accumulation of integral term of an integral action for a duration between a time point at which the actual secondary pressure starts to be pushed down and a time point at which the same-pressure state between the line pressure and the secondary pressure is realized.