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 varying input speeds and torques, and are prone to rollback issues due to limited control over tilt and skew angles.
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 seamless switching between forward and reverse directions and maintaining stability and sensitivity through axial and radial translations of trunnion extensions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If traditional CVT designs are used, then the structure is simple, but the ability to switch between forward and reverse directions while maintaining stable speed ratios is poor
Solution Approach 1:
The patent implements dynamic control of tilt and skew angles through independently controllable actuators that adjust the planet carrier assembly's orientation in real-time. This allows the CVT to adapt its kinematic parameters dynamically during operation, enabling seamless transition between forward and reverse directions while maintaining stable speed ratios, thereby resolving the contradiction between enhanced adaptability and increased system complexity.
Solution Approach 2:
The patent changes key kinematic parameters (tilt angle and skew angle) of the planet carrier assembly to achieve different operational modes. By independently controlling these parameters through dedicated actuators, the system can switch between forward and reverse directions and adjust speed ratios without fundamental structural changes, thus improving direction switching capability while managing complexity through parameter-based control.
2Reliability
If tilt and skew angles are not independently controlled, then the control system is simple, but rollback issues occur and speed ratio stability is poor
Solution Approach 1:
The patent incorporates feedback control mechanisms that continuously monitor the actual tilt and skew angles of the planet carrier assembly and adjust the actuator positions accordingly. This closed-loop control ensures precise maintenance of desired kinematic parameters, preventing rollback issues and ensuring speed ratio stability, while the feedback system manages complexity by using standard control algorithms rather than overly complex mechanical designs.
Solution Approach 2:
The patent introduces intermediary components (actuators and linkages) that mediate between the control system and the planet carrier assembly. These intermediaries provide precise control over tilt and skew angles, enabling independent adjustment of each parameter to prevent rollback and maintain stability, while the modular nature of these intermediaries helps manage overall system complexity.
3Measurement precision
If independent control of tilt and skew angles is implemented, then speed ratio adjustment precision is improved, but device complexity increases
Solution Approach 1:
The patent segments the control function into two independent subsystems: one dedicated to controlling tilt angle and another for skew angle. Each subsystem has its own actuator, allowing precise independent control of each kinematic parameter. This segmentation improves speed ratio control precision by eliminating cross-coupling effects, while the modular segmented architecture helps manage complexity by dividing the control task into manageable independent units.
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.