Bicycle CVT and Motor Control for Automatic Ratio Adjustment
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Solution Overview
Problem
Existing bicycles often require manual operation of transmissions, and electric motors struggle to provide constant power at variable speeds without increasing size, cost, or complexity, while existing CVT systems do not effectively integrate with bicycle crankshafts.
Innovation Solution
A bicycle with a continuously variable transmission (CVT) system that includes traction planets, sun members, and carrier members, integrated with an electric motor, and controlled by an electronic controller to automatically adjust transmission ratios based on user input and speed sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If manual operation of transmission is used in bicycles, then device complexity is reduced, but ease of operation deteriorates due to requiring manual actuation of levers and cables
Solution Approach 1:
The transmission system automatically adjusts gear ratios based on sensor inputs (cadence, speed, torque) without requiring manual intervention. The control system processes user inputs and autonomously actuates the transmission mechanism, allowing the system to serve itself rather than requiring continuous manual operation.
Solution Approach 2:
The patent replaces manual mechanical cable actuation with an electronic control system that uses sensors and actuators. The control system electronically processes input data and automatically controls transmission ratios, substituting the traditional mechanical cable-pull shifting mechanism with an automated electro-mechanical system.
2Force
If electric motor size is increased to provide sufficient low speed torque, then torque increases, but weight and volume increase
Solution Approach 1:
The CVT dynamically adjusts the transmission ratio in real-time based on operating conditions (speed, torque requirements, cadence). This allows a smaller motor to deliver high torque at low speeds by using the transmission system to multiply the motor's output, rather than requiring the motor itself to be oversized for all conditions.
Solution Approach 2:
The continuously variable transmission acts as an intermediary between the electric motor and the wheel. It transforms the motor's output characteristics, providing torque multiplication at low speeds without requiring the motor to be physically larger. The CVT mediates the power transmission to achieve the desired torque output from a compact motor.
3Power
If CVT is integrated with electric motor, then constant power at variable speeds is achieved, but device complexity increases
Solution Approach 1:
The control system performs multiple functions: it processes sensor data (cadence, speed, torque), determines optimal transmission ratios, controls the CVT actuator, and manages motor output. This multi-functional control architecture achieves constant power delivery across variable speeds while consolidating control logic into a single integrated system rather than separate control mechanisms.
4Ease of operation
If automatic transmission control is implemented, then ease of operation improves, but device complexity increases due to electronic controllers and sensors
Solution Approach 1:
The system uses feedback from sensors (cadence sensor, speed sensor, torque sensor) to continuously monitor operating conditions and automatically adjust transmission ratios. This closed-loop feedback control enables automatic operation without manual intervention, with the control system processing sensor inputs and making real-time adjustments to maintain optimal performance.
Data Source
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AI summary
A continuously variable transmission (CVT) can be used in concert with an electric motor to facilitate power assistance to a rider in a bicycle. In some embodiments, the CVT and motor is mounted on the frame of the bicycle at a location forward of the rear wheel hub of the bicycle. In some embodiments, the CVT is mounted on and supported by members of the bicycle frame such that the CVT is coaxial with the crankshaft of the bicycle. The crankshaft is configured to drive elements of the CVT, which are configured to operationally drive the traction rings and the traction planets. In some embodiments, the motor is configured to drive elements of the CVT. In other embodiments, the motor is configured to drive the crankshaft. Inventive component and subassemblies for such a CVT are disclosed.