Motor Shaft Voltage Suppression via Capacitance Balancing
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Solution Overview
Problem
Inverters using PWM methods create shaft voltage differences in motor bearings, leading to electrolytic corrosion, which conventional methods struggle to effectively suppress due to issues with electrical continuity, insulation, and electrostatic capacitance balance.
Innovation Solution
A motor design with a stator, rotor, conductive brackets, and a lead wire conductive member that adjusts electrostatic capacitance between the shaft and stator core to maintain balanced electrical potentials, reducing shaft voltage and preventing electrolytic corrosion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If electrical insulation is maintained between inner ring and outer ring of bearing, then electrolytic corrosion is suppressed, but shaft voltage increases due to unbalanced electrostatic capacitance
Solution Approach 1:
The patent changes the electrical parameters (electrostatic capacitance) of the bearing system by introducing a conductive member or dielectric layer with specific capacitance values. This parameter adjustment balances the electrical potentials between inner and outer rings, reducing shaft voltage while maintaining electrical insulation to prevent electrolytic corrosion.
2Object-affected harmful factors
If shaft voltage is reduced by electrically shorting stator core to metal bracket, then electrolytic corrosion is suppressed, but electrostatic capacitance cannot be adjusted and shaft voltage rises with certain magnet materials and rotor structures
Solution Approach 1:
The patent introduces a dynamic adjustment mechanism for electrostatic capacitance through the conductive member or dielectric layer. Unlike fixed electrical shorting, this structure allows the capacitance to be adjusted according to different magnet materials and rotor structures, providing adaptability while suppressing shaft voltage and electrolytic corrosion.
3Reliability
If electrostatic capacitance is increased to suppress electrolytic corrosion, then bearing protection is improved, but balance of electrostatic capacitance is difficult to maintain under high electric potential and varying environmental conditions
Solution Approach 1:
The patent creates a feedback mechanism where the conductive member or dielectric layer with controlled capacitance responds to changes in electrical potential and environmental conditions. The structured capacitance design provides stability by maintaining balanced electrical potentials even under varying conditions, preventing electrolytic corrosion while ensuring reliable operation.
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 motor effectively suppresses electrolytic corrosion in bearings by maintaining balanced electrical potentials and reducing shaft voltage, preventing dielectric breakdown and noise issues, even under varying environmental conditions.
Implementation Method 1
electrostatic capacitance A formed between the shaft and an outermost surface to be the farthest outer periphery from the axial center of the rotary body; electrostatic capacitance B formed between the stator core and the conductive member
Implementation Method 2
maintain balanced electrical potentials, reducing shaft voltage
Implementation Method 3
If the shaft voltage reaches a breakdown voltage of an oil film present in the bearing, a micro electric current flows inside the bearing. This flow of the micro electric current causes electrolytic corrosion in the bearing
Data Source
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AI summary
A motor of the invention comprises a stator, a rotor, a pair of bearings, a pair of brackets and a conductive member. The stator has a winding, and a stator core on which the winding is wound. The rotor has a rotary body including a permanent magnet disposed in a circumferential direction and confronting the stator, and a shaft penetrating through an axial center of the rotary body and fixed to the rotary body. The pair of bearings supports the shaft. The pair of brackets has electrical conductivity, and fixes the bearings. The conductive member electrically connects the pair of brackets. There is a relation of 0.50A ≤ B ≤ 3.08A at a measuring frequency of 10 kHz, where A denotes an electrostatic capacitance formed between the shaft and an outermost surface of the rotary body at a farthest outer periphery from the axial center, and B denotes an electrostatic capacitance formed between the stator core and the conductive member.