CVT Reverse Rollback Control via Skew Angle Inversion
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Solution Overview
Problem
Continuously variable transmissions (CVTs) face instability and potential damage when operating in reverse direction due to positive feedback from angled guide slots, leading to extreme underdrive or overdrive conditions, which can result in transmission torque loss exceeding available drive torque and potential damage to rolling contacts.
Innovation Solution
A system and method for controlling rollback in CVTs, involving a processor communicatively coupled to an actuator, which executes a set of instructions to adjust the skew angle of planet axles, counteracting positive feedback by rotating carriers in a direction opposite to the initial skew, and using a timing plate with offset radial slots to limit skew and ratio errors, ensuring each planet remains within a controlled ratio angle and limited skew angle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the CVT operates in reverse direction using angled guide slots, then the transmission can achieve reverse motion, but positive feedback causes instability and extreme ratio conditions
Solution Approach 1:
The patent applies reverse skew angle commands during reverse operation to counteract the positive feedback effect of angled guide slots. By inverting the skew angle control strategy (applying negative skew angles instead of positive), the system stabilizes the transmission ratio and prevents runaway conditions while maintaining reverse motion capability
Solution Approach 2:
The control module continuously monitors transmission operation and dynamically adjusts skew angle commands based on detected conditions. During reverse operation, the system uses feedback control to detect ratio extremes and applies corrective skew angle adjustments to maintain stable operation, preventing the positive feedback loop that would otherwise cause instability
2Ease of operation
If skew angle commands are applied during reverse operation, then ratio control is achieved, but machining errors and load droop cause inaccuracies
Solution Approach 1:
The control module applies preliminary skew angle offset commands before reverse operation begins and maintains these offset commands throughout reverse operation. This preliminary action compensates for anticipated machining errors and load-induced droop in skew angle, improving the accuracy of ratio control during reverse operation
Solution Approach 2:
The system dynamically changes skew angle parameters based on operating conditions. During reverse operation, the control module adjusts skew angle magnitude and direction to compensate for machining tolerances and load variations, maintaining accurate ratio control despite physical imperfections in the mechanical components
3Stability of the object's composition
If rollback control is implemented with multiple commands, then stability is improved, but system complexity increases
Solution Approach 1:
The control module uses the existing actuator and control infrastructure to implement rollback control, making the system self-sufficient. By utilizing the same hardware components already present in the CVT system and implementing control logic within the existing control module, the patent achieves enhanced stability without proportionally increasing overall system complexity
Data Source
AI summary
A continuously variable transmission capable of operating in a forward direction or reverse direction may be controlled in the reverse direction by providing an initial skew angle in a first skew direction, followed by a set or sequence of skew angle adjustments in an opposite direction to prevent runaway or other unintended consequences. A continuously variable transmission may include a timing plate to maintain all planets at an angle or within a range of an angle in forward and reverse operations.