Pedelec Drive Unit With Nested Wave Gear for Narrow Axial Width
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Solution Overview
Problem
Existing drive units for pedelecs and similar vehicles face challenges in being narrow enough to accommodate human anatomy while maintaining functionality, as they require space for pivot bearings, gearboxes, and electric motors, leading to increased width and discomfort during long distances.
Innovation Solution
A drive unit design featuring an input drive shaft connected to a wave gear system with a flexspline and ring gear, allowing for compact arrangement of a drive electric motor within the wave gear's sleeve, and using a ring gear as a transmission output to minimize axial width, along with strategically placed pivot bearings and freewheels to optimize space usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If traditional drive units are positioned on the bottom bracket or wheel hub, then they can provide sufficient power transmission capability, but they increase the axial width and protrude beyond the wheel or crank arms
Solution Approach 1:
The electric motor is nested within the hollow cylindrical sleeve of the wave gear mechanism. The motor's stator is positioned inside the sleeve's interior space, allowing the motor to be housed within the existing gear structure rather than requiring separate mounting space. This nesting arrangement significantly reduces the overall axial width of the drive unit while maintaining both the motor's power transmission capability and the wave gear's speed reduction function.
2Length of stationary object
If the drive unit is made narrower to fit between crank arms, then riding comfort improves, but the space required for pivot bearings, gearboxes, and electric motors becomes insufficient
Solution Approach 1:
The invention transitions from a conventional side-by-side or stacked arrangement of components to a radial/dimensional arrangement where the electric motor is positioned in the radial direction within the wave gear's hollow sleeve. This dimensional reorganization allows pivot bearings, the wave gear mechanism, and the electric motor to coexist in a compact axial profile by utilizing the radial space within the sleeve, thereby accommodating all necessary components within a narrower axial envelope.
3Length of stationary object
If the electric motor is positioned outside the wave gear, then assembly is simpler, but the drive unit width increases beyond acceptable limits
Solution Approach 1:
The electric motor is nested within the hollow cylindrical sleeve of the wave gear mechanism. The motor's stator is positioned inside the sleeve's interior space, allowing the motor to be housed within the existing gear structure rather than requiring separate mounting space. This nesting arrangement significantly reduces the overall axial width of the drive unit while maintaining both the motor's power transmission capability and the wave gear's speed reduction function.
Solution Approach 2:
The hollow cylindrical sleeve of the wave gear mechanism serves multiple functions: it acts as the structural housing for the wave gear mechanism, provides the mounting structure for pivot bearings, and simultaneously serves as the housing for the electric motor. This multi-functionality eliminates the need for separate motor housing and mounting structures, simplifying the overall assembly while achieving compact dimensions.
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 results in a compact drive unit that is flexible and capable of covering the full range of functions, providing a comfortable pedaling experience by minimizing the axial width and maintaining efficient power transmission, while allowing for precise control and energy recuperation.
Implementation Method 1
a wave gear arranged around a rotational axis, including a wave generator, a flexspline, and a ring gear
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
The invention relates to a means of transport (F), in particular pedelec, which can be driven by means of drive energy produced electromotively and by human muscular power, comprising a drive unit (1) in which an electric drive motor (27) and a harmonic drive transmission (18) are nested one inside the other, thereby saving space.