E-Bike Multispeed Drive Unit With Cam-Assisted Smooth Shifting
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Solution Overview
Problem
Existing electric bicycles lack efficient multispeed drive units that provide smooth and reliable gear shifting, especially under varying riding conditions, leading to suboptimal pedaling cadence and motor assistance.
Innovation Solution
A multispeed drive unit with a torque transmission device featuring a camshaft assembly, shift motor, and gear reducer system, which includes alignment features and a spring mechanism to facilitate smooth gear shifting and reduce shifting forces, allowing for a compact and cost-effective design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a traditional gear shifting mechanism is used, then the structure is simple, but the shifting forces are high and transitions are jerky
Solution Approach 1:
The patent applies dynamics by making the lever movably attached to the hollow shaft, allowing it to move dynamically during gear shifting operations. This mobility enables the lever to adapt its position during shifting, reducing the force required and smoothing the transition between gears, while maintaining structural simplicity.
Solution Approach 2:
The cam profile acts as an intermediary element between the lever and the gear shifting mechanism. The cam's specially designed profile mediates the force transmission, distributing the shifting forces over a longer period and reducing peak forces, while enabling smooth gear transitions through controlled mechanical interaction.
2Volume of moving object
If a compact drive unit design is pursued, then the overall size is reduced, but the gear shifting mechanism becomes more complex
Solution Approach 1:
The patent implements nesting by placing the cam inside the hollow shaft, and the lever within the cam assembly. This nested arrangement allows multiple components to occupy overlapping spatial volumes, significantly reducing the overall drive unit size while containing the gear shifting mechanism within a compact footprint.
Solution Approach 2:
The invention utilizes the hollow shaft's internal space by placing the cam and lever mechanism within it, effectively using the third dimension (internal volume) to accommodate complex shifting components without increasing the external dimensions of the drive unit, thus achieving compactness without excessive complexity.
3Productivity
If multiple gears are integrated into a single drive unit, then the transmission efficiency is improved, but the device complexity increases
Solution Approach 1:
The patent merges multiple gear ratios and the motor assembly into a single integrated drive unit. The hollow shaft contains multiple cams for different gears, and the motor is integrated within the same housing, creating a unified transmission system that improves efficiency by eliminating intermediate connections while managing complexity through modular internal arrangement.
Solution Approach 2:
The hollow shaft serves multiple functions simultaneously: it acts as a structural support, a housing for the cam mechanism, a mounting structure for gears, and a rotational element for power transmission. This multi-functionality reduces the need for separate components, improving transmission efficiency while containing the overall device complexity.
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 multispeed drive unit provides improved shifting performance with reduced shifting forces, smoother transitions, and efficient motor assistance, enhancing the overall riding experience by adapting to different riding conditions.
Implementation Method 1
The torque transmission device further includes a spring disposed within the groove. The spring has a first end and a second end opposite the first end. The first end of the spring is attached to the first shaft at a position along the groove, and the second end of the spring is attached to the lever, such that the lever is biased away from the outer circumferential surface of the first shaft.
Implementation Method 2
The torque transmission device includes a cam attached to and extending away from the outer circumferential surface of the second shaft, and a gear rotatably attached to the first shaft over the opening, the gear comprising internal teeth.
Implementation Method 3
The tooth of the lever is engageable with the internal teeth of the gear, and the foot of the lever is configured to contact the cam extending away from the outer circumferential surface of the second shaft.
Data Source
AI summary
A torque transmission device for a drive unit of a bicycle includes a shaft having an opening extending through the shaft. The torque transmission device includes a lever having a seat, a foot, and a tooth. The lever is movably attached to the shaft, such that the seat of the lever is rotatable on a surface of the shaft at least partially defining the opening. The tooth of the lever is engageable with internal teeth of a gear disposable about the shaft, and the foot of the lever is engageable with a cam disposable within the shaft. The lever is movably attached to the shaft, such that the foot of the lever is biased away from the outer circumferential surface of the shaft. A distance between the seat and the foot is greater than a distance between the tooth and the seat.