CVT Shift Speed Control via Surplus Oil Calculation
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Solution Overview
Problem
Continuous variable transmissions (CVTs) face issues with oil insufficiency during tip-in situations, leading to excessive shift speeds and subsequent damper pressure decrease, making it impossible to maintain target line pressure.
Innovation Solution
A method to control shift speed by calculating surplus oil pump RPM and amount, determining allowable shift speed based on these calculations, and adjusting shift speed to prevent oil insufficiency, incorporating driving mode considerations to optimize shift speed limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If down shift is performed by supplying oil to driven pulley in tip-in situation, then shift speed increases, but surplus oil amount decreases causing inability to follow target line pressure
Solution Approach 1:
The controller calculates the allowable shift speed in advance based on current transmission state (engine RPM, turbine torque, oil temperature) before executing the down shift. This preliminary calculation ensures that the shift speed is predetermined to not exceed limits that would deplete surplus oil amount, thus preventing line pressure control failure.
Solution Approach 2:
The controller continuously monitors transmission state parameters (engine RPM, turbine torque, oil temperature) and uses this feedback to dynamically adjust the allowable shift speed. This feedback mechanism ensures that shift speed control adapts to changing conditions while maintaining sufficient surplus oil amount for line pressure control.
2Speed
If shift speed exceeds allowable limit, then down shift performance improves, but damper pressure decreases causing damper release
Solution Approach 1:
The controller calculates the allowable shift speed in advance considering the relationship between shift speed and damper pressure. By predetermined the maximum allowable shift speed based on current transmission state, the system prevents excessive shift speed that would cause damper pressure decrease and damper release.
Solution Approach 2:
The controller monitors transmission state and dynamically adjusts the allowable shift speed to maintain appropriate damper pressure. This feedback-based adjustment ensures that shift operations do not compromise damper pressure while achieving desired shift performance.
Data Source
AI summary
A method for controlling a shift speed of a continuous variable transmission includes: a first calculating step for calculating a surplus oil pump RPM based on a transmission oil temperature, an engine RPM, and a turbine torque; a second calculating step to calculate a surplus oil amount based on the surplus oil pump RPM, the transmission oil temperature, the engine RPM, and a line pressure; a third calculating step to calculate an allowable shift speed based on the surplus oil amount and a current gear ratio; a shift speed comparing step to compare the shift speed of a vehicle with the allowable shift speed; and a shift speed controlling step in which the controller varies the shift speed or the allowable shift speed to control the shift speed to be equal to or less than the allowable shift speed when the shift speed exceeds the allowable shift speed.