Triangular Driving Unit for Electric Assist Bicycle Axial Size Reduction
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Solution Overview
Problem
Existing electric assist bicycle driving units are difficult to miniaturize in the axial direction of the crankshaft due to the linear arrangement of the motor, rotating member, and gear reducer, limiting size reduction.
Innovation Solution
The driving unit incorporates a housing with a crankshaft, motor, and transmission shaft, where the motor, first and second transmission gears, and driven gear are arranged to form a triangular configuration with overlapping components, allowing the smallest component to be positioned closer to the others, thereby reducing the unit's size in the axial direction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the motor, rotating member, and gear reducer are arranged in a linear configuration along the crankshaft axis, then the structural simplicity and ease of assembly are improved, but the axial size of the driving unit increases
Solution Approach 1:
The patent transitions from a linear one-dimensional arrangement to a two-dimensional planar configuration. The motor, first transmission gear, second transmission gear, and driven gear are arranged in a triangular layout with overlapping projections, utilizing the radial dimension around the crankshaft axis to reduce axial length while maintaining functional relationships.
Solution Approach 2:
The patent implements nesting by positioning components such that their projections overlap when viewed from the axial direction. The first transmission gear overlaps with the motor, the second transmission gear overlaps with both the motor and first transmission gear, creating a compact nested arrangement that minimizes axial footprint.
2Length of moving object
If the components are arranged in a compact overlapping configuration, then the axial size is reduced, but the structural complexity increases
Solution Approach 1:
The patent employs asymmetric triangular arrangement of components rather than symmetric linear placement. The motor, first transmission gear, and driven gear form a specific triangular configuration with defined overlap relationships, optimizing space utilization while maintaining manufacturability through clear asymmetric positioning guidelines.
Data Source
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AI summary
A driving unit for use in an electric assist bicycle with reduced size as viewed in an axial direction of the crankshaft is provided. Out of a motor, first transmission gear and driven gear, a first component is the component with the largest diameter as viewed in an axial direction of the crankshaft, a second component is the component with the second largest diameter, and a third component is the component with the smallest diameter. One of the first and second components is the driven gear. As viewed in an axial direction of the crankshaft, at least part of the first component overlaps the second component. At least part of the third component overlaps the area where the first and second components overlap. A first line segment connecting the rotational center of the first component with the rotational center of the second component, a second line segment connecting the rotational center of the second component with the rotational center of the third component, and a third line segment connecting the rotational center of the third component with the rotational center of the first component form a triangle. The first line segment is longer than the second line segment and longer than the third line segment.