Rolling-Element Shaft Coupling for Misalignment Without Axial Thrust
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Solution Overview
Problem
Existing powertrains with axial flux electric machines face performance and lifespan issues due to misalignment and axial forces between the output shaft and primary shaft, leading to variations in air gaps and increased stress on bearings, which are exacerbated by gearbox-induced axial thrusts.
Innovation Solution
A coupling device with a support base and rolling elements is introduced to maintain relative positions, allowing for the transmission of high torques while compensating for misalignment and preventing the transmission of axial forces, using a mechanism similar to a 'ball slide' to accommodate shaft misalignments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If splines are used to couple the output shaft and primary shaft, then the shafts can slide relative to each other to accommodate misalignment, but axial forces are transmitted causing component displacement and increased bearing stress
Solution Approach 1:
The patent introduces rolling elements (balls) as an intermediary between the output shaft and primary shaft. These rolling elements engage with grooves in both shafts and are contained within a support base, creating a ball slide mechanism that transmits torque while preventing axial force transmission. The rolling elements act as a mediator that allows relative movement without direct axial force coupling between the shafts.
2Reliability
If the rotor support bearings are sized to handle increased stress from axial forces, then bearing reliability is improved, but the electric machine weight increases significantly
Solution Approach 1:
The rolling elements serve as an intermediary mechanism that prevents axial forces from being transmitted to the rotor support bearings. By introducing this ball slide coupling between the output shaft and primary shaft, the bearings only need to support the actual rotor weight and normal operational loads, not the excessive axial thrust forces, thereby maintaining reliability without requiring oversized bearings.
3Power
If deeper grooves and more rolling elements are used in the coupling device, then torque transmission capability is improved, but the device complexity increases
Solution Approach 1:
The coupling device is segmented into distinct functional components: the support base with multiple arms, the rolling elements, and the grooves in the shafts. The support base is divided into several parallel arms (at least three, preferably at least six, and even more preferably eight), with each arm carrying retaining means for rolling elements. This segmentation allows for systematic increase in torque capacity by adding more arms and rolling elements without creating a monolithic complex structure.
Solution Approach 2:
The patent extends the coupling device in the radial dimension by adding multiple parallel arms extending from the junction part. This dimensional approach allows torque transmission capacity to be increased by distributing rolling elements across multiple arms rather than concentrating them in a single location, thereby scaling power capacity while maintaining a organized, manageable 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
This solution maintains the geometric integrity of the air gaps and extends the lifespan of bearings by preventing power loss and reducing stress on the electric machine components, ensuring consistent performance.
Implementation Method 1
rolling elements adapted to be engaged in grooves provided in the shafts, and a support base adapted to hold the rolling elements engaged in the grooves in relative position
Data Source
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AI summary
The invention relates to a shaft coupling device (300) comprising: - rolling elements (310) to be engaged in grooves provided in shafts to be coupled; and - a holding base (320) enabling the rolling elements to be held in position in the grooves. According to the invention, the holding base comprises a joining portion from which a plurality of parallel arms extend, wherein each of the parallel arms bears at least one means for retaining one of the rolling elements.