Ball-Planetary CVT Control for Stable Forward and Reverse Ratios
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Solution Overview
Problem
Existing continuously variable transmissions (CVTs) face challenges in efficiently switching between forward and reverse directions while maintaining stable speed ratios and torque control, particularly in scenarios involving rollback or changing load conditions.
Innovation Solution
The implementation of a control system that adjusts the offset angle (psi) and skew angle (zeta) of trunnions relative to the pitch circle, allowing for independent control of tilt angles (gamma) and speed ratios, enabling the CVT to operate in both forward and reverse directions with enhanced stability and sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a CVT operates in forward direction, then speed ratio control is maintained, but switching to reverse direction causes instability and rollback
Solution Approach 1:
The patent implements dynamic adjustment of the offset angle (psi) of trunnions based on operating conditions. The control system continuously monitors direction of rotation and adjusts the offset angle to have opposite signs for forward and reverse directions, enabling the CVT to adapt its geometric configuration dynamically. This dynamic reconfiguration maintains stability during direction switching while enabling versatile bidirectional operation.
Solution Approach 2:
The patent changes geometric parameters (offset angle psi and skew angle zeta) based on operating conditions. By adjusting the offset angle to opposite signs for forward and reverse rotation, and independently controlling tilt angles and speed ratios, the system resolves the contradiction between maintaining stability and enabling direction switching. These parameter changes allow the CVT to optimize performance for each direction while transitioning smoothly between them.
2Adaptability or versatility
If the offset angle (psi) is adjusted for direction switching, then reverse operation is enabled, but control sensitivity may be reduced
Solution Approach 1:
The control system dynamically adjusts the offset angle (psi) based on the detected direction of rotation. When reverse operation is required, the system changes the offset angle to have the opposite sign compared to forward operation. This dynamic adjustment enables reverse direction operation while the control system compensates for any sensitivity changes through active feedback control, maintaining precise speed ratio and torque control throughout the transition.
Solution Approach 2:
The patent employs a control system that monitors operating conditions including direction of rotation and actively adjusts geometric parameters (offset angle psi, skew angle zeta) and speed ratios in response. This feedback mechanism compensates for potential sensitivity reductions during direction switching, maintaining control precision by continuously optimizing parameters based on real-time operational state.
3Productivity
If tilt angles (gamma) are independently controlled, then speed ratio adjustment is improved, but device complexity increases
Solution Approach 1:
The patent makes the offset angle (psi) serve multiple functions: it enables direction switching (by changing sign between forward and reverse) and simultaneously facilitates speed ratio adjustment (by magnitude variation). This multi-functionality allows independent control of tilt angles and speed ratios without proportionally increasing device complexity, as the same geometric parameter adjustment mechanism achieves both objectives.
Solution Approach 2:
The patent combines the functions of direction control and speed ratio control into a unified geometric configuration system. By adjusting the offset angle (psi) and skew angle (zeta) of trunnions, the system simultaneously controls both the direction of rotation and the speed ratio. This merging of control functions into a single integrated mechanism improves productivity while minimizing the increase in device complexity compared to separate control systems.
Data Source
AI summary
A ball-planetary continuously variable transmission (CVT) capable of stable control in forward and reverse rotation over a range of speed ratios including underdrive and overdrive is provided. Imparting a skew angle (zeta) causes unbalanced forces that change the tilt angle (gamma), resulting in a change in speed ratio of the CVT. Angularly orientating a control system of the CVT with a positive offset angle (psi) configures the CVT for operation in a first direction of rotation or angularly orientating the control system with a negative offset angle (psi) configures the CVT for operation in a reverse direction of rotation. A control system for configuring the offset angle (psi) may lead or trail the planets. The control system may configure a larger offset angle for more stable control or may configure a smaller offset angle for higher sensitivity in potential rollback scenarios.