Gear System Noise Suppression via Resistive Grounding
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Solution Overview
Problem
Existing solutions for reducing high-frequency noise radiation in electric vehicles, such as grounding the output shaft via a brush, are ineffective due to insufficient electric resistance at the brush contact, allowing noise to propagate through the power transmission system and suspensions.
Innovation Solution
A power transmission device with a gear set that includes electrically resistive elements interposed between the rotor shaft and the grounding path, effectively increasing the resistance and reducing noise radiation by grounding a part of the gear set, thereby suppressing noise propagation from the inverter to the drive shafts and suspensions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a brush is used to ground the output shaft, then noise propagation is expected to be prevented, but the electric resistance at the brush is not sufficiently low and noise can flow beyond the brush contact point
Solution Approach 1:
The patent introduces electrically resistive elements (such as carbon brushes with specific resistance values, resistors, or gear meshing interfaces) as intermediary components between the rotor shaft and the grounding path. These intermediaries increase the electrical resistance in the noise propagation path, effectively blocking high-frequency noise from traveling through the power transmission system while still providing a grounding path for lower frequency interference.
Solution Approach 2:
The patent modifies the electrical resistance parameter along the noise propagation path by incorporating components with specific resistance values. For example, carbon brushes are selected with resistance values between 0.1 to 10 ohms, or resistors are added to create intentional high-resistance zones that block noise propagation while maintaining grounding functionality.
2Object-affected harmful factors
If the brush contact resistance is reduced to prevent noise flow, then noise propagation is suppressed, but achieving sufficiently low resistance is not readily accomplished
Solution Approach 1:
Rather than attempting to create a low-resistance brush contact (which is manufacturingally difficult), the patent uses high-resistance intermediary elements to block noise. The resistive elements serve as mediators that intentionally create high resistance to prevent noise propagation, turning the manufacturing difficulty into a design feature.
Solution Approach 2:
The patent converts the naturally occurring electrical resistance in brush contacts (which was previously seen as a harmful limitation) into a beneficial noise-blocking feature. By selecting brushes or adding resistors with specific resistance values, the natural resistance becomes an effective noise suppression mechanism rather than a problem to be overcome.
3Object-affected harmful factors
If the grounding path is established at the output shaft, then noise propagation is intended to be blocked, but noise leaks out of the output shaft toward the power transmission system and suspensions
Solution Approach 1:
The patent segments the grounding path into multiple sections with different resistance characteristics. By placing resistive elements at specific locations (such as at the rotor shaft or input shaft rather than the output shaft), the noise propagation path is divided into zones with different electrical properties, effectively blocking noise at strategic points while maintaining grounding elsewhere.
Solution Approach 2:
Instead of grounding the output shaft as previously attempted, the patent inverts the approach by establishing the grounding path with resistive elements at the rotor shaft or input shaft. This reverse approach blocks noise at its source before it can propagate through the power transmission system, achieving better noise suppression than grounding at the output shaft.
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 significantly reduces noise radiation to the exterior by increasing the resistance in the noise propagation path, as demonstrated by reduced noise intensities measured in decibels, effectively mitigating the issue of high-frequency noise interference.
Implementation Method 1
an electric resistance at the brush is not sufficiently low and therefore the noise can flow beyond a part with which the brush contacts. To reduce noise propagation, it is promising to reduce the resistance at the brush.
Data Source
AI summary
A power transmission device for a vehicle is comprised of a motor including a rotor shaft and a stator having an electromagnetic coil; an inverter configured to generate an alternating current, the inverter being connected with the coil to controllably rotate the rotor shaft relative to the stator; a gear set including an input shaft coupled with and rotated by the rotor shaft, an output shaft and gears so meshed as to transmit torque of the input shaft to the output shaft; and a grounding path electrically connecting a part of the gear set with a body of the vehicle, the part being so disposed as to have the input shaft electrically interposed between the part and the rotor shaft.