Bicycle Assist Unit Planetary Gear Shifting Mechanism
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Solution Overview
Problem
Conventional bicycle assist units face difficulties in shifting performance due to high torque applied to the ring gear, making it challenging to apply brakes and impacting shifting efficiency.
Innovation Solution
A bicycle assist unit with a planetary gear mechanism and a rotation restricting mechanism that selectively restricts the rotation of ring gears, combined with a gear reduction mechanism and a sensor to detect manual drive force, allowing for improved shifting performance by reducing the load on the pawl portions and enhancing the detachment process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If torque from the assist motor is applied before gear ratio change in the transmission, then the motor can provide assistance force, but the shifting performance deteriorates due to difficulty in applying brakes to the ring gear
Solution Approach 1:
The power transmission path is segmented into two separate paths: one path transmits motor torque from the assist motor to the output shaft, and another path transmits manual torque from the crankshaft to the output shaft through the planetary gear mechanism. This segmentation allows independent control of torque application timing, enabling the ring gear brake to effectively restrict ring gear rotation during shifting while the assist motor provides torque through a different route that does not interfere with the shifting mechanism.
2Force
If high torque is applied to the ring gear during motor assistance, then the assist force is sufficient, but the braking of ring gear becomes difficult and shifting efficiency decreases
Solution Approach 1:
The transmission system is divided into separate torque transmission paths where motor torque and manual torque are transmitted independently. The motor torque path bypasses the ring gear, allowing the ring gear brake to apply sufficient braking force during shifting without competing against high motor torque. This resolves the conflict between providing sufficient assist force and maintaining high shifting efficiency.
Solution Approach 2:
A separate transmission path acts as an intermediary between the assist motor and the output shaft, allowing motor torque to be transmitted without passing through the ring gear. This intermediary path enables the ring gear brake to function effectively during shifting while the assist motor continues to provide necessary torque through the alternative route.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution improves shifting performance by reducing the time required for shifting and preventing shifting failures, while also reducing the size of the assist unit and allowing for more precise control of the assist motor, thus enhancing the overall riding experience.
Implementation Method 1
The transmission includes a planetary gear mechanism for transmitting the drive force from the motor to propel the bicycle
Implementation Method 2
a rotation restricting mechanism that selectively restricts rotation of the ring gears
Data Source
AI summary
A bicycle assist unit is basically provided with a transmission and an assist motor. The transmission is configured to receive rotation of a crankshaft. The transmission includes a planetary gear mechanism. The planetary gear mechanism includes an output unit, a plurality of ring gears and a rotation restricting mechanism that selectively restricts rotation of the ring gears. The assist motor is configured to output a second drive force that is added to a first drive force that is outputted from the transmission on a power transmission path between the output unit and a front sprocket that is attached to the crankshaft.