Insulating Device for Electric Machine Collector
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Solution Overview
Problem
The existing insulating devices for electric machine collectors, particularly in motor vehicle alternators, face issues with micro-cracks in the overmolded plastic parts during force-fitting, leading to compromised electrical insulation due to the fragility of the insulating material at weld zones, allowing current to leak through to the rotor shaft.
Innovation Solution
An insulating device with a protection element and an indexing element is introduced, where the protection element is positioned between the shaft and the slip rings to prevent microcrack propagation, and the indexing element maintains an axial gap between the slip rings, ensuring effective insulation. The protection element includes guide zones and a rim for controlled positioning, and the device can be made from thermoplastic, thermosetting, or composite materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If force-fitting is used to mount the collector on the shaft, then secure mechanical attachment is achieved, but micro-cracks occur in the overmolded plastic part compromising electrical insulation
Solution Approach 1:
The insulating device is segmented into distinct functional zones: an indexing element with an annular flange for maintaining axial gap between slip rings, and a protection element with guiding zones for isolating connection zones. This segmentation allows each element to perform its specific function optimally without compromising the other during force-fitting.
Solution Approach 2:
The indexing element and protection element are pre-positioned on the shaft before the collector is force-fitted. The indexing element maintains the axial gap between slip rings in advance, and the protection element positions itself to isolate connection zones before micro-cracks can propagate, preventing insulation failures proactively.
2Reliability
If the overmolded plastic material is used for insulation, then electrical insulation is provided, but the material fragility at weld zones allows current leakage through micro-cracks
Solution Approach 1:
The protection element acts as an intermediary barrier between the shaft and the connection zones where traces are welded to slip rings. This intermediate structure prevents stress concentration at the fragile weld zones during force-fitting, eliminating the root cause of micro-crack formation in the overmolded plastic material.
Solution Approach 2:
The protection element provides localized reinforcement and stress distribution at the connection zones between traces and slip rings. Instead of requiring the entire overmolded plastic part to have high deformation capacity, the local quality enhancement at critical weld zones prevents micro-crack initiation while maintaining overall insulation reliability.
3Volume of moving object
If slip rings are positioned close together, then compact design is achieved, but electrical insulation between slip rings cannot be guaranteed
Solution Approach 1:
The indexing element with its annular flange is positioned beforehand to maintain a precise axial gap between the two slip rings. This pre-established spacing acts as a cushion that prevents electrical breakdown between slip rings while minimizing the overall volume occupied by the collector assembly.
Data Source
Figure 1a~1b
Figure 2a~2c
Figure 2d~2e
AI summary
The invention mainly concerns an insulating device for a collector (5) of an electric machine intended for being press-fit onto a rotor shaft (8) of an electric machine, said collector (5) comprising two slip rings (6a, 6b) each connected to a strip (7a, 7b), characterised by comprising a protection element (2) intended for being at least partially arranged between said shaft (8) and said slip rings (6a, 6b), said protection element (2) being configured to insulate at least one area for connecting one of the strips (7a, 7b) to the corresponding slip ring (6a, 6b) relative to said shaft (8), prior to overmoulding the assembly.