Bicycle Drive Unit Segmentation for Retrofitting
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Solution Overview
Problem
Existing wheel hub drives for vehicles, particularly bicycles, are heavy, difficult to retrofit, and interfere with free wheel rotation when not energized, making them unsuitable for sport-oriented bikes and retrofitting.
Innovation Solution
A drive unit comprising a wheel unit with a gear ring and guide profiles, and a motor unit with a motor carrier that is movably supported and circumferentially fixed, allowing for easy installation and engagement with the wheel, enabling accurate gear engagement and reducing unsprung mass at the rear wheel axis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a wheel hub drive is used, then the electric motor can be integrated into the wheel, but the weight increases and retrofitting becomes difficult
Solution Approach 1:
The drive unit is divided into separate components: a motor unit that can be independently mounted to the frame, and a wheel unit with gear ring and guide profile that attaches to the wheel. This segmentation allows the motor to be positioned separately from the wheel hub, enabling retrofitting without replacing the entire wheel assembly and reducing the effective unsprung mass at the wheel axis.
Solution Approach 2:
A motor carrier serves as an intermediary component between the frame and the wheel unit. The motor carrier is movably supported by guide wheels running on the guide profile, allowing it to accommodate wheel deformations while maintaining proper gear engagement. This intermediary structure enables easy installation and removal for retrofitting applications.
2Ease of operation
If a wheel hub drive is used, then the motor is integrated into the wheel, but the wheel cannot rotate freely when the motor is not energized
Solution Approach 1:
The motor carrier is designed to be movable rather than fixed, allowing it to dynamically adjust its position as the wheel rotates and deforms. The guide wheels enable the motor carrier to follow the guide profile path, maintaining proper engagement conditions between the drive pinion and gear ring throughout the wheel rotation cycle, including during free rotation when the motor is not energized.
Solution Approach 2:
The system allows the engagement parameters between the drive pinion and gear ring to change dynamically as the wheel deforms under load. The motor carrier's movable support enables it to accommodate these parameter changes without preventing free wheel rotation, maintaining reliable engagement only when needed while allowing free rotation when the motor is disengaged.
3Reliability
If the motor carrier is rigidly fixed to the frame, then the structure is stable, but it cannot accommodate wheel deformation and eccentricity errors
Solution Approach 1:
The motor carrier transitions from a rigid fixed connection to a dynamically movable support system. The guide wheels enable the motor carrier to move along the guide profile, allowing it to accommodate wheel eccentricity errors and dynamic deformations while maintaining accurate gear engagement between the drive pinion and gear ring throughout operation.
4Reliability
If the motor unit is heavily constructed for stability, then the engagement is reliable, but the weight increases and sport applications are compromised
Solution Approach 1:
The drive system is segmented into a relatively lightweight motor unit mounted to the frame and a wheel unit with the gear mechanism. This segmentation allows the use of lighter materials and construction in the motor unit while maintaining engagement reliability through the precision guide profile and movable carrier design, making the system suitable for sport-oriented bicycle applications where weight is critical.
Data Source
AI summary
The drive unit (19) according to the invention for light vehicles, in particular bicycles, comprises a wheel unit (20) and a motor unit (21). The wheel unit (20) includes a gear ring (27) and at least one, preferably two support tracks (31, 35) on which the motor unit (21), which is movably supported but circumferentially fixed to the frame (11), runs. In this way, a wheel-support arrangement for the motor unit (21) is provided. As a result, also with extreme light-weight designs as used in connection with bicycles even in sport applications, a correct engagement between the wheel mounted gear ring (27) and drive pinion (45) is achieved.