Wheel Hub Motor Potential Equalization via Spring Contact
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Solution Overview
Problem
In electrically driven vehicles, electromagnetic fields induce voltages in the rotor, causing bearing currents and potential dielectric breakdown in the lubricant of rolling element bearings, leading to premature aging and electromagnetic interference, which is not compliant with EMC regulations.
Innovation Solution
A wheel hub motor design with a spring-loaded contact element creating an electrically conductive connection between the bearing rings, supported against the hub, which includes a potential equalization element to prevent bearing currents and electromagnetic interference, using a simple and cost-effective manufacturing approach.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a contact element is provided to create an electrically conductive connection between bearing rings, then bearing currents are prevented and lubricant degradation is minimized, but device complexity increases
Solution Approach 1:
A contact element is introduced as an intermediary component to create an electrically conductive path between the inner and outer bearing rings. This mediator prevents bearing currents from flowing through the lubricant, thereby protecting the lubricant from electrochemical degradation and extending bearing lifespan.
Solution Approach 2:
The electrical connection path is segmented into distinct components: the contact element and the potential equalization element. This segmentation allows each component to be optimized independently - the contact element for electrical conductivity and the potential equalization element for mechanical stability and manufacturability.
2Reliability
If a spring is used to support the contact element against the hub, then reliable electrical contact is maintained, but manufacturing complexity increases
Solution Approach 1:
The contact element is made dynamically adjustable through the spring mechanism. The spring allows the contact element to automatically adapt its position to maintain reliable electrical contact despite variations in assembly tolerances, thermal expansion, or wear over time, without requiring complex adjustment mechanisms.
Solution Approach 2:
The spring mechanism enables the contact element to change its positional parameter dynamically. By allowing controlled movement within a range defined by the spring's elastic properties, the system maintains optimal contact pressure and electrical conductivity under varying operating conditions.
3Ease of manufacture
If the potential equalization element is configured as a covering cap, then manufacturing cost is reduced through deep drawing, but contact surface area is limited
Solution Approach 1:
The potential equalization element is designed as a simple covering cap that can be mass-produced through deep drawing, a cost-effective manufacturing process. This simplified design prioritizes manufacturing economy while still fulfilling its essential function of providing a counter-face for pressure contact.
Solution Approach 2:
The covering cap design concentrates the electrical contact function at the specific location where it is most needed - at the interface with the contact element. The rest of the cap structure can be minimized, allowing the majority of the surface area to be reduced without compromising the critical contact function.
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 effectively minimizes the aging of rolling element bearings, prevents electromagnetic wave emission, and enhances manufacturing efficiency and visual appeal while maintaining electromagnetic compatibility.
Implementation Method 1
the contact element being supported against the hub via a spring
Implementation Method 2
creating an electrically conductive connection between said bearing rings
Implementation Method 3
the electromagnetic fields generated by the stator may induce voltages in the rotor
Implementation Method 4
the rolling elements are spaced by a lubricant film from at least one of the bearing rings
Implementation Method 5
the electrically insulating lubricant is of limited dielectric strength
Data Source
AI summary
A wheel hub motor for driving a motor vehicle is provided. Aging of the rolling element bearings used to support the rotor is prevented, while at the same time minimizing the emission of electromagnetic waves, in that the wheel hub motor includes a—rotor,—a hub (1), —a wheel bearing having a first bearing ring (2) which is non-rotatably and electrically conductively connected to the hub (1), and a second bearing ring (3) which is non-rotatably and electrically conductively connected to the rotor, and—a contact element (4) for creating an electrically conductive connection between said bearing rings (2, 3), the contact element (4) being supported against the hub (1) via a spring (6) and has a pressure contact with a potential equalization element (5) that is non-rotatably and electrically conductively connected to the second bearing ring (3).