Bicycle Auxiliary Drive with Nested Planetary Gear
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Solution Overview
Problem
Conventional electric auxiliary drives for bicycles are bulky, heavy, and recognizable due to their large drive system, making them difficult to use for sporty cycling, especially when riders need assistance or are temporarily injured, and they are not inconspicuous.
Innovation Solution
An electric auxiliary drive system with a compact design that fits within a bicycle frame's seat tube or down tube, utilizing a planetary gear with a stepped tooth configuration and an electric motor, allowing for coaxial or parallel geometric axes of rotation, reducing weight and visibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a conventional electric auxiliary drive system is installed around the crank axle, then the bicycle can be propelled by electric motor assistance, but the system weight becomes high and the bicycle is easily recognizable as an e-bike
Solution Approach 1:
The drive unit is nested within the bicycle frame's seat tube or down tube. The drive housing is inserted into the tube, and the motor and planetary gear unit are arranged coaxially within this housing, creating a compact integrated assembly that fits inside the frame structure rather than adding external bulk
Solution Approach 2:
The drive axis is oriented parallel to the longitudinal axis of the seat tube or down tube, utilizing the vertical dimension of the frame rather than horizontal space around the crank axle. This reorientation allows the drive system to be concealed within the frame's structural tubes
2Power
If a conventional electric auxiliary drive system is installed around the crank axle, then the bicycle can be propelled by electric motor assistance, but the bicycle becomes easily recognizable as an e-bike from the outside
Solution Approach 1:
The drive housing is inserted into the seat tube or down tube of the bicycle frame, concealing the motor and planetary gear unit within the frame's existing structure. This nesting approach hides the drive system components from external view, making the bicycle appear conventional
Solution Approach 2:
By reorienting the drive axis to be parallel to the longitudinal axis of the frame tubes rather than perpendicular around the crank axle, the system utilizes the frame's internal volume and maintains the traditional bicycle silhouette from all external viewing angles
3Power
If a conventional electric auxiliary drive system is installed around the crank axle, then the bicycle can be propelled by electric motor assistance, but the drag torque of the drivetrain in unassisted riding mode becomes high
Solution Approach 1:
The planetary gear unit is designed with a freewheel mechanism that allows it to be disengaged from the drivetrain. When the electric motor is not providing assistance, the freewheel permits the planetary gear unit to decouple from the crankshaft, eliminating the drag torque that would otherwise be generated by the gearbox during unassisted pedaling
Solution Approach 2:
The drivetrain incorporates a freewheel mechanism that dynamically engages or disengages the planetary gear unit based on whether electric motor assistance is active. This dynamic coupling allows the system to transition between assisted and unassisted modes without constant mechanical connection, reducing parasitic losses
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 provides a lightweight, efficient, and quiet auxiliary drive with reduced vibrations and higher efficiency, enabling sporty cycling without the bulkiness of conventional systems, while being discreetly integrated into the bicycle frame.
Implementation Method 1
The planetary gear unit (18) is operatively connected to the motor shaft (19) on the drive side. On the output side, the planetary gear unit (18) can be operatively connected to a bicycle crankshaft (11)... The planetary gear set comprises a first central gear (20), a second central gear (21), and a carrier (22). At least one planet gear (23) is rotatably mounted on the carrier (22)... The planet gear (23) is stepped and has a first toothed section zp1 and a second toothed section zp2
Data Source
Figure 1
Figure 2~3
Figure 4~5
AI summary
An electric auxiliary drive for a bicycle is proposed, comprising a drive housing (16) that fits into a seat tube or down tube of a conventional bicycle frame, an electric motor (17) arranged in the drive housing (16) which drives a motor shaft (19) to rotate about a geometric drive axis (14), a planetary gear (18) housed in the drive housing (16) which is operatively connected to the motor shaft (19) on the drive side and can be operatively connected to a pedal crank shaft (11) of a bicycle on the output side such that the drive axis (14) and the geometric axis (12) of the pedal crank shaft (11) intersect at right angles, the planetary gear (18) being equipped with a first central gear (20), a second central gear (21), a bridge (22) and at least one stepped planet gear (23, 33).The planet gear (23, 33) meshes with the first central gear (20) via a first toothed section (23a, 33a). The planet gear (23, 33) meshes with the second central gear (21) via a second toothed section (23b, 33b) that differs from the first toothed section.