E-Bike Drive Unit Bearing Restraint for Thrust Rattle Control
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Solution Overview
Problem
Electrically assisted bicycles with drive units mounted at the lower end of the body frame experience rattling issues due to thrust loads, which can be perceived as abnormal movement by users accustomed to generic bicycles, as existing solutions fail to adequately address the axial play needed for mechanical parts.
Innovation Solution
A drive unit design that includes a housing with an electric motor, a pedal crank shaft supported by bearings, and a movement restrictor comprising an abutting portion, a groove, and an elastic member, where the elastic member deforms to prevent movement along the thrust direction under normal loads and allows movement when loads exceed the compression force, dispersing the load across additional abutting portions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If bearings are used to support the pedal crank shaft, then the pedal crank shaft can rotate smoothly, but thrust loads cause axial movement and rattling along the thrust direction
Solution Approach 1:
The patent introduces a bearing as an intermediary component between the pedal crank shaft and the housing. The bearing's inner ring is press-fitted to the pedal crank shaft while the outer ring is free-fitted in the housing, allowing the bearing to mediate between rotational support and axial movement restriction. This intermediary component enables smooth rotation while the elastic member and abutting portion provide axial position stability.
Solution Approach 2:
The patent changes the fitting parameters of the bearing: the inner ring uses a press-fit connection (interference fit) to prevent radial movement relative to the pedal crank shaft, while the outer ring uses a free-fit connection (clearance fit) to allow radial movement. This parameter change enables the bearing to accommodate both rotational smoothness and axial position control requirements.
2Stability of the object's composition
If an elastic member is added to restrict bearing movement, then rattling is reduced, but the device complexity increases
Solution Approach 1:
The patent merges multiple functions into the elastic member: it acts as both a movement restrictor for the bearing and a load dispersal mechanism. The elastic member is integrated into the housing structure, combining the functions of axial positioning and load absorption into a single component, thereby reducing overall device complexity despite adding functionality.
Solution Approach 2:
The elastic member serves multiple purposes: it restricts bearing movement along the thrust direction to prevent rattling, absorbs thrust loads, and provides a compliant connection that accommodates normal operational variations. This multi-functionality reduces the need for separate components for each function.
3Strength
If the elastic member is made more compliant to allow movement, then load dispersal is improved, but rattling increases
Solution Approach 1:
The patent creates a dynamic system where the elastic member's compliance is optimized to provide just enough movement to disperse loads while maintaining sufficient stiffness to prevent rattling. The elastic member's properties are designed to be dynamically responsive to applied loads, providing rigidity under normal conditions and compliance under excessive loads.
Solution Approach 2:
The patent carefully selects and adjusts the elastic member's material properties and geometric parameters (such as wire diameter, mean diameter, and number of active coils for spring elements) to achieve the optimal balance between compliance for load dispersal and stiffness for preventing rattling. These parameter changes enable the elastic member to fulfill both contradictory requirements.
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
Significantly reduces or prevents rattling of the pedal crank shaft along the thrust direction, ensuring smooth operation and user satisfaction by effectively managing thrust loads and maintaining the integrity of the mechanical components.
Implementation Method 1
an elastic member fitted in the groove... the elastic member urges the outer wheel from the second end surface side toward the first end surface side
Data Source
AI summary
A drive unit of an electrically assisted bicycle includes a movement restrictor to restrict the movement of a first bearing relative to a housing along a thrust direction. A first end surface of the first bearing is farther outward than a second end surface along the right-left direction. The housing includes an abutting portion that abuts the first end surface of the first bearing, and a groove that is farther inward than the abutting portion along the right-left direction. The movement restrictor includes the abutting portion, the groove of the housing, and an elastic member fitted in the groove.