E-Bike Powertrain Layout for Low Unsprung Mass and Protected Gearing
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Solution Overview
Problem
Electric bicycles face challenges with powertrains that are either heavy due to hub motors at the rear wheel, increasing unsprung mass and affecting rear suspension performance, or require maintenance-prone derailleur systems that are exposed to the elements.
Innovation Solution
A powertrain design for electric bicycles featuring an electric motor, motor gear, crankshaft, input shaft, gears, countershaft, and shift assemblies, with a torque sensor for motor control, and a cycloidal drive for efficient power transmission, housed in a protective structure to minimize weight and maintenance needs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a hub motor is provided at the rear wheel to propel the bicycle, then motorized propulsion is achieved, but the mass of the rear wheel assembly increases and unsprung mass increases which is not desirable for rear suspension performance
Solution Approach 1:
The motor is extracted from the rear wheel hub and relocated to a separate mounting position on the bicycle frame. This separation removes the heavy motor components from the rear wheel assembly, reducing unsprung mass and improving suspension performance while maintaining the ability to provide motorized propulsion assistance.
2Productivity
If a derailleur system is used to provide variable-ratio gearing, then the system is efficient and lightweight, but the system is exposed to the elements which affects durability and requires regular maintenance
Solution Approach 1:
The derailleur system is merged with the rear suspension assembly, integrating the gearing components into a protected enclosure. This integration shields the derailleur from direct exposure to environmental elements such as water and dirt, improving durability and reducing maintenance requirements while maintaining gearing efficiency.
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 powertrain provides efficient, lightweight, and low-maintenance propulsion assistance while minimizing the impact on rear suspension systems and reducing exposure to environmental elements, enhancing the overall performance and durability of electric bicycles.
Implementation Method 1
an electric motor; a motor gear operatively connected to and driven by the electric motor
Implementation Method 2
a cycloidal drive for efficient power transmission
Data Source
AI summary
A powertrain for an electric bicycle has: an electric motor; a motor gear driven by the electric motor; a crankshaft adapted for connecting to crank arms; an input shaft having first and second end portions, the second end portion driven by the crankshaft; an input gear connected to the first end portion and being driven by the motor gear, the input gear driving the input shaft; at least one first gear mounted to the input shaft; an output shaft; at least one second gear mounted to the output shaft and being driven by the at least one first gear; a drive sprocket driven by the output shaft; and a torque sensor disposed between the second end portion and the at least one first gear for sensing torque applied to the input shaft. The electric motor is controlled based at least in part on torque sensed by the torque sensor.