Brushless DC Motor Shielding via Capacitive Coupling
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Solution Overview
Problem
Conventional brushless DC motors with small capacity emit electromagnetic waves due to their design, and existing shielding solutions, such as metallic plates and rotor shielding, require complex and unreliable sliding contacts to ground, which are costly and prone to service life issues.
Innovation Solution
The DC motor employs capacitive coupling through sintered bearings to connect the rotor shielding to a defined electrical potential, eliminating the need for sliding contacts and enhancing high-frequency interference discharge by using a pot-shaped metallic rotor housing and additional sintered bearings for improved capacitive coupling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If sliding contacts are used to connect the rotor shielding to ground, then electrical connection is achieved, but service life is reduced and reliability is worsened
Solution Approach 1:
The patent replaces the mechanical sliding contact system with a capacitive coupling system. The rotor shielding is connected to ground potential through a capacitor formed by the bearing assembly, eliminating mechanical wear and improving reliability. The capacitor consists of the rotor shielding as one electrode and the stator ground as the other, with the bearing grease and air gap forming the dielectric.
Solution Approach 2:
The patent introduces a capacitor as an intermediary element between the rotor shielding and ground. This capacitor allows AC coupling of the shielding potential without requiring direct galvanic connection, thereby eliminating the need for sliding contacts while maintaining effective electromagnetic shielding.
2Object-affected harmful factors
If metallic shielding plates are added to reduce electromagnetic waves, then shielding effectiveness is improved, but device complexity and cost increase
Solution Approach 1:
The patent makes the rotor housing serve dual functions: it acts as both the structural containment for rotor components and as the electromagnetic shielding element. By forming the rotor housing from conductive material and capacitively coupling it to ground, the same component provides both mechanical and electromagnetic functions, eliminating the need for separate shielding plates.
Solution Approach 2:
The patent merges the rotor housing structure with the electromagnetic shielding function. The conductive rotor housing is integrated with the capacitive coupling system, combining what would traditionally be separate components (structural housing and shielding plate) into a single unified element.
3Reliability
If galvanic coupling through sintered bearing is used, then electrical connection is achieved, but high-frequency interference discharge is insufficient
Solution Approach 1:
The patent changes the electrical connection parameter from galvanic (direct conductive) coupling to capacitive coupling. This parameter change allows the system to effectively discharge high-frequency interference while maintaining the mechanical functionality of the sintered bearing. The capacitive impedance decreases with increasing frequency, making it effective for high-frequency noise suppression.
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 provides effective and cost-efficient shielding by capacitive coupling, reducing electromagnetic interference and extending the motor's service life by eliminating the need for sliding contacts.
Implementation Method 1
a connection which is particularly electrically conductive in the high-frequency range, namely a capacitive electrical coupling, is used by means of the sintered bearing to connect the rotating shaft to a stationary bearing bushing
Implementation Method 2
the at least partially electrically insulating, oil-filled bearing gap which is arranged between the shaft and the sintered bearing
Implementation Method 3
the high-frequency interferences which are generated by the motor and couple into the rotor shielding can be better discharged via the capacitive coupling to the mass potential
Data Source
AI summary
In an electronically commutated DC motor having a stator unit (5) and a rotor unit (1) which is in the form of an external rotor, and having stationary sintered bearings (8, 9), the invention proposes that the rotor unit (1) is conductively connected to the shaft (3) in order to connect a conductive shielding, which is formed on the rotor unit (1), to a defined electrical potential, and that the sintered bearing (8, 9) is conductively connected to the potential, so that the shielding of the rotor unit (1) is capacitively coupled to the potential by means of the electrically insulating, oil-filled bearing gap which is arranged between the shaft (3) and the sintered bearing (8, 9). Therefore, a sliding contact is not required.