Bicycle Drive Unit Layout With Intersecting Motor and Crank Axes
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Solution Overview
Problem
In bicycle drive units, it is challenging to reduce the size of the propulsion assist motor portion parallel to the crankshaft's rotational axis due to the parallel alignment of the motor's rotational axis with the crankshaft's, which limits the compactness of the system.
Innovation Solution
The bicycle drive unit design incorporates a housing with a propulsion assist motor whose rotational axis intersects the crankshaft's axis, allowing for a smaller footprint in the direction parallel to the crankshaft, with specific dimensions and configurations to optimize space utilization and torque output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the rotational axis of the propulsion assist motor is aligned parallel to the rotational axis of the crankshaft, then the motor can be simply mounted, but the size of the drive unit in the direction parallel to the crankshaft axis cannot be reduced
Solution Approach 1:
The patent changes the orientation of the propulsion assist motor from parallel alignment with the crankshaft axis to intersecting alignment, where the motor's rotational axis intersects the crankshaft axis at a specific angle. This dimensional reorientation allows the motor to be positioned in a different spatial configuration, reducing the overall length of the drive unit in the direction parallel to the crankshaft axis while maintaining mounting feasibility.
2Volume of moving object
If the second portion of the housing is reduced in size to improve compactness, then the overall drive unit becomes more compact, but the space for accommodating the propulsion assist motor becomes insufficient
Solution Approach 1:
By changing the motor's rotational axis from parallel to intersecting with the crankshaft axis, the patent creates a more efficient three-dimensional spatial arrangement. This allows the second portion of the housing to be compact in the direction parallel to the crankshaft axis while maintaining adequate accommodation space for the motor through the intersecting orientation, effectively utilizing available volume without compromising motor housing requirements.
Solution Approach 2:
The patent employs asymmetric design in the housing structure, where the second portion has different dimensional constraints in different directions. Specifically, the dimension in the direction parallel to the crankshaft axis is limited to 75 mm or less, while the dimension in the direction orthogonal to the motor's rotational axis is maintained at 40 mm or more. This asymmetric dimensional allocation optimizes compactness in the critical direction while preserving motor accommodation capability.
3Length of moving object
If the dimension of the second portion in the direction orthogonal to the motor's rotational axis is reduced to 75 mm or less, then compactness is improved, but the motor arrangement space becomes too constrained
Solution Approach 1:
The patent applies asymmetric dimensional constraints to the second portion of the housing, setting the dimension in the direction orthogonal to the motor's rotational axis at 75 mm or less for compactness, while simultaneously ensuring the dimension in the direction parallel to the crankshaft axis remains 40 mm or more. This asymmetric approach achieves compactness in the critical direction without overly constraining the motor arrangement space in other directions.
Solution Approach 2:
The patent specifies a dynamic range for the rotational angle between the motor's rotational axis and the crankshaft axis, setting it between 0 degrees and 90 degrees. This dynamic parameter allows flexibility in optimizing the motor's position and orientation within the constrained space, enabling proper motor arrangement while maintaining the compact dimensional requirements.
Data Source
AI summary
A bicycle drive unit includes a housing, crankshaft and a propulsion assist motor. The housing is configured to be mounted on a frame of a bicycle. The housing includes a first portion and a second portion. The crankshaft is provided to the first portion of the housing. The propulsion assist motor is provided to the second portion of the housing and configured to assist propulsion of the bicycle. The propulsion assist motor includes a rotational axis extending in a direction intersecting a direction in which the crankshaft extends. The second portion has a maximum dimension of smaller than or equal to 75 mm in a direction orthogonal to the rotational axis of the propulsion assist motor.