CVT Ratio Control via Gradient Constraints
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Solution Overview
Problem
Conventional continuously variable transmissions (CVTs) fail to meet driver and passenger expectations, leading to perceptions of engine slippage or malfunction due to their inability to maintain engine speed in direct proportion with vehicle speed, and compromise between optimal fuel economy and predefined ratio maps that cater to discrete gear ratio expectations.
Innovation Solution
A system and method that determines the current gear ratio, calculates a projected ratio from a predetermined map, and adjusts the CVT ratio in real-time to satisfy a gradient constraint, allowing switching between optimal ratio paths while maintaining compliance with predefined expectations, using a processor to control the CVT ratio based on driver input and vehicle conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a predefined ratio map is used to optimize fuel economy, then fuel efficiency is improved, but driver expectations are not met causing perception of slippage or malfunction
Solution Approach 1:
The system dynamically adjusts the CVT ratio by calculating gradients between current and projected ratios, and modifying control ratios in real-time based on gradient constraints. This dynamic adjustment allows the system to balance fuel economy optimization with maintaining engine speed behavior that meets driver expectations, resolving the contradiction between fuel efficiency and driver perception of proper operation.
2Productivity
If the CVT continuously varies the gear ratio to optimize performance, then efficiency is improved, but engine speed does not increase in direct proportion with vehicle speed
Solution Approach 1:
The system implements feedback by continuously monitoring the gradient between current CVT ratio and projected ratio from the ratio map, and adjusting the control ratio based on gradient constraints. This feedback mechanism ensures that the CVT maintains optimal efficiency while preventing engine speed from decreasing or remaining flat during vehicle acceleration, thereby maintaining the expected proportional relationship between engine speed and vehicle speed.
3Reliability
If a predefined ratio map with constrained gradient is used, then driver expectations are met, but fuel economy optimization is compromised
Solution Approach 1:
The system changes parameters by calculating the gradient between current and projected ratios, and dynamically adjusting the control ratio based on gradient constraints. This parameter adjustment allows the system to follow fuel-economy-optimized ratio paths while ensuring that the gradient remains within constraints that satisfy driver expectations, thereby resolving the contradiction between fuel economy optimization and compliance with driver expectations.
Data Source
AI summary
A method and system for controlling a ratio of a continuously variable transmission coupling a prime mover to a driven member in a vehicle. The method includes determining a current ratio of the continuously variable transmission, determining a projected ratio from a first ratio path of a predetermined ratio map, calculating a gradient between the current ratio and the projected ratio, determining whether the calculated gradient satisfies a gradient constraint, setting a control ratio to the projected ratio if the calculated gradient satisfies the gradient constraint, setting a control ratio to a modified ratio if the calculated gradient does not satisfy the gradient constraint, the modified ratio being based upon a ratio that satisfies the gradient constraint, and controlling the ratio of the continuously variable transmission to the control ratio.