E-Bike Powertrain Gearbox Layout for Lower Unsprung Rear Wheel Mass
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Solution Overview
Problem
Existing electric bicycles face challenges with powertrains that are either heavy due to hub motors at the rear wheel, affecting unsprung mass in rear suspension systems, or require maintenance-prone derailleur systems.
Innovation Solution
A powertrain design for electric bicycles featuring an electric motor, gear system, and shift assemblies with a torque sensor for motor control, housed in a protective configuration to reduce weight and maintenance needs, including a cycloidal drive and sprag clutches for efficient torque transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a hub motor is provided at the rear wheel, then the electric motor can propel the bicycle without pedaling, but the mass of the rear wheel assembly increases, affecting unsprung mass in rear suspension systems
Solution Approach 1:
The patent extracts the electric motor from the rear wheel hub location and relocates it to the frame near the crankshaft. This separation removes the heavy motor mass from the unsprung rear wheel assembly, reducing unsprung mass while maintaining the ability to provide motorized propulsion assistance through the gear system
Solution Approach 2:
The patent introduces a gear system as an intermediary mechanism between the electric motor and the rear wheel. The motor drives the rear wheel through a series of gears (input gear, intermediate gears, output gear) rather than direct hub motor connection, allowing torque transmission while keeping the motor separate from the wheel assembly
2Weight of moving object
If a derailleur is used to provide a variable-ratio gearing system, then the system is efficient and lightweight, but it is exposed to the elements which could affect its durability and requires regular maintenance
Solution Approach 1:
The patent merges the gear system with the electric motor housing, creating an integrated transmission assembly. The gears are enclosed within the motor housing rather than being exposed on the bicycle frame, protecting them from environmental elements and reducing maintenance requirements while maintaining variable-ratio gearing functionality
Solution Approach 2:
The patent uses an enclosed housing structure to protect the internal gear system from exposure to elements. The housing acts as a protective shell that shields the gears from water, dust, and other environmental factors that would otherwise require regular maintenance
3Reliability
If a gearbox transmission is associated with the pedelec's crank, then the system provides smooth transition between gears and is durable, but it is heavier than a derailleur system
Solution Approach 1:
The patent combines the gearbox transmission functions directly within the electric motor housing, merging two separate systems (motor and transmission) into one integrated unit. This consolidation provides smooth gear transitions and durable operation while minimizing the overall weight by eliminating separate transmission components
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
This design reduces weight by optimizing motor placement and gear system efficiency, while minimizing maintenance through the use of a torque sensor for motor control and a robust gear system, enhancing performance and durability.
Implementation Method 1
a robust gear system
Implementation Method 2
including a cycloidal drive and sprag clutches for efficient torque transfer
Data Source
AI summary
A powertrain (100) for an electric bicycle has: an electric motor (104); a motor gear (226) connected to the motor (104); a crankshaft (108) for connecting to crank arms (110); an input shaft (232) driven by the crankshaft (108); an input gear (234) connected to the input shaft (232) and driven by the motor gear (226); a plurality of first gears (236) mounted to the input shaft (232); a countershaft (242); a plurality of second gears (244) rotationally mounted to the countershaft (242), each second gear being driven by a corresponding first gear (236); a plurality of third gears (246) rotationally mounted to the countershaft (242); an output shaft (114); a plurality of fourth gears (260) mounted to the output shaft (114), each fourth gear (260) being selectively driven by a corresponding third gear (246); a first shift assembly (248) for selectively rotationally fixing any one second to the countershaft (242); a second shift assembly (250) for selectively rotationally fixing any one third gear (246) to the countershaft (242); and a drive sprocket (116) driven by the output shaft (114).