Coaxial Bicycle Drive Unit With Nested Freewheel Clutches
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Solution Overview
Problem
Existing drive units for manually powered vehicles, such as bicycles and EPACs, have complex structures with numerous individual components, leading to inefficiencies in space utilization and design optimization.
Innovation Solution
A drive unit with a coaxial arrangement of the pedal crankshaft and output shaft, incorporating one-way clutches, an electric auxiliary drive with a strain wave gear, and a compact design that allows for central placement of components like an electronics unit and electric motor, utilizing an external rotor motor and a stator carrier for efficient power transmission and torque measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a complex structure with numerous individual components is used (as in prior art), then the drive unit can accommodate all necessary functions, but the space utilization is inefficient and the design is not optimized
Solution Approach 1:
The patent merges the pedal crankshaft and output shaft into a single coaxial structure, and integrates the one-way clutches directly onto the output shaft. This consolidation reduces the number of separate components and improves space utilization while maintaining all necessary functions.
Solution Approach 2:
The output shaft is designed as a hollow shaft that surrounds the pedal crankshaft axially. The one-way clutches are nested within the hollow cross-section of the output shaft, with control elements positioned between the inner and outer rings. This nested arrangement maximizes space efficiency within the compact drive unit structure.
2Volume of moving object
If components are arranged centrally around the crankshaft, then the design becomes more compact, but the mechanical coupling and torque transmission become more complex
Solution Approach 1:
The output shaft serves multiple functions: it acts as the output member for power transmission, provides the mounting structure for both one-way clutches, and forms the hollow structural element that enables compact central arrangement. This multi-functionality reduces the need for additional separate components.
Solution Approach 2:
The drive unit is segmented into functional zones along the axial direction, with the pedal crankshaft in the center, one-way clutches at different axial positions, and the electric auxiliary drive surrounding these components. This segmentation allows for systematic mechanical coupling while maintaining compact overall dimensions.
3Volume of moving object
If one-way clutches are arranged radially between the pedal crankshaft and output shaft, then space is optimized, but the assembly and manufacturing become more difficult
Solution Approach 1:
The one-way clutches are pre-assembled with their control elements and then integrated into the hollow output shaft structure. The pedal crankshaft is pre-mounted in the center position before the final assembly of the complete drive unit. This preliminary assembly approach simplifies the overall manufacturing process.
Solution Approach 2:
The hollow output shaft acts as an intermediary structure that holds and positions the one-way clutches radially between the pedal crankshaft and the outer housing. This intermediary structure simplifies the mechanical coupling by providing a unified mounting platform for multiple components.
4Power
If an electric auxiliary drive with strain wave gear is incorporated, then power transmission efficiency is improved, but the device complexity increases
Solution Approach 1:
The electric auxiliary drive with strain wave gear is integrated into the existing coaxial structure, sharing the same central axis as the pedal crankshaft and output shaft. The strain wave gear's flexspline is coupled to the output shaft, merging the electric and manual drive paths into a unified mechanical structure.
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 solution achieves a compact and efficient design that optimizes space utilization, facilitates easy assembly, and enables reliable torque measurement while reducing the risk of electronic damage, thus enhancing the performance and durability of the drive unit.
Implementation Method 1
a strain wave gear (20), wherein the flexspline (32) is coupled to the second one-way clutch (26)
Implementation Method 2
a first one-way clutch (24) and a second one-way clutch (26), which are axially adjacent to one another and act on the output shaft (22)
Data Source
Figure 1
Figure 2
Figure 3
AI summary
The invention relates to a drive unit (10) for a manually driven vehicle, in particular a bicycle or an EPAC, comprising a housing (12), a bottom bracket shaft (14), an electric auxiliary drive (16), and an output shaft (22) designed as a hollow shaft, wherein the bottom bracket shaft (14) and the output shaft (22) are coaxial to each other, and the output shaft (22) surrounds the bottom bracket shaft (14) radially outwards at least in some sections axially. A first freewheel clutch (24) and a second freewheel clutch (26) are arranged radially between the bottom bracket shaft (14) and the output shaft (22), said freewheel clutches being axially adjacent to each other and acting on the output shaft (22).