Electric Motor Insulating Body for Electro-Pitting Prevention
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Electric motors with permanent magnets face issues of electro-pitting in ball bearings due to eddy currents from the rotor main body to the shaft, leading to electrical discharges and potential connection failure.
Innovation Solution
An insulating body made of a ceramic and synthetic material compound is used to create a rotationally-fixed, electrically insulating connection between the rotor main body and the shaft, preventing eddy currents and enhancing mechanical strength, while guiding magnetic flux efficiently.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a press-fit connection is used between the shaft and rotor main body, then a rotationally-fixed connection is achieved, but electrical insulation cannot be provided and electro-pitting occurs
Solution Approach 1:
An insulating body is introduced as an intermediary element between the shaft and rotor main body. This insulating body serves dual functions: it provides electrical insulation to prevent eddy currents from reaching the ball bearings (avoiding electro-pitting), and it establishes a rotationally-fixed connection through engagement features such as keys or splines. The intermediary element resolves the contradiction by enabling both electrical isolation and mechanical coupling without requiring a direct press-fit connection.
Solution Approach 2:
The insulating body is constructed from composite materials, typically combining a ceramic core (such as aluminum oxide or silicon nitride) with a synthetic material jacket (such as epoxy resin or polyimide). The ceramic portion provides high mechanical strength and rigidity to transmit torque, while the synthetic material provides electrical insulation and flexibility. This composite structure enables the insulating body to simultaneously achieve mechanical strength for torque transmission and electrical insulation for preventing electro-pitting.
2Reliability
If only synthetic material is used for the insulating body, then electrical insulation is provided, but mechanical strength decreases and serviceable life is reduced
Solution Approach 1:
The insulating body employs a composite structure with a ceramic core surrounded by a synthetic material jacket. The ceramic core (aluminum oxide, silicon nitride, or silicon carbide) provides high mechanical strength, hardness, and thermal stability to withstand the mechanical loads and torque transmission requirements. The synthetic material jacket (epoxy resin, polyimide, or PTFE) provides electrical insulation, flexibility, and bonding capability. This composite configuration synergistically combines the advantages of both materials to achieve both high mechanical strength and adequate electrical insulation, thereby extending the serviceable life of the connection.
Solution Approach 2:
Different regions of the insulating body are assigned different material properties to fulfill different functional requirements. The central core region uses ceramic material optimized for mechanical strength and torque transmission, while the outer jacket region uses synthetic material optimized for electrical insulation and environmental protection. This local differentiation of material quality allows each region to perform its specific function optimally, resolving the contradiction between mechanical strength and electrical insulation requirements.
3Reliability
If the insulating body engages into grooves in both shaft and rotor main body, then a rotationally-fixed connection is achieved, but manufacturing complexity increases
Solution Approach 1:
The insulating body acts as a mediator that incorporates engagement features (such as keys, splines, or protrusions) designed to fit into corresponding grooves or keyways in both the shaft and rotor main body. These engagement features are integrated into the insulating body's structure during its manufacturing process (such as molding or machining), allowing the grooves to be formed in the shaft and rotor main body using standard machining operations. The mediator absorbs the complexity of the connection geometry, enabling the use of conventional manufacturing methods for the shaft and rotor main body while achieving a reliable rotationally-fixed connection.
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 prevents electro-pitting, increases the serviceable life of the shaft-hub connection, and optimizes magnetic flux guidance within the rotor main body, ensuring reliable torque transmission and improved motor efficiency.
Implementation Method 1
So-called electro-pitting that may occur in ball bearings that are provided for mounting the shaft is avoided by way of the electric motor in accordance with the invention. Said electro-pitting occurs if eddy currents are directed out of the rotor main body via the shaft to the ball bearings and cause electrical discharges there.
Implementation Method 2
The ceramic core is particularly advantageously designed as a press ring. This means that the ceramic core has an annular shape and is connected to the shaft via an interference fit assembly. Consequently, it is possible in particular in addition to the previously described positive-locking connection to also establish an at least in part functioning non-positive locking connection.
Data Source
AI summary
The present invention relates to an electric motor (1) comprising a rotor main body (2), to which a plurality of permanent magnets (3) or a rotor winding can be attached, and a shaft (4) for receiving the rotor main body (2), characterized in that an isolation body (5) is arranged between the shaft (4) and the rotor main body (2) to electrically isolate the rotor main body (2) from the shaft (4), in that the isolation body (5) engages at least partially into the shaft (4) and into the rotor main body (2) in order to connect the shaft (4) and rotor main body (2) for conjoint rotation, and in that the isolation body (5) is made from a composite of ceramic and plastic.