EV Gear Shaft and Rotor Shaft Layout for Helical Gear NV Reduction
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Solution Overview
Problem
In electric vehicles with helical gears, the thrust force generated by gear meshing reactions can cause noise and vibration (NV) issues due to the transmission of this force to the rotor shaft and subsequently to the casing members.
Innovation Solution
The electric vehicle design includes a gear shaft with a large diameter portion and a rotor shaft with a stepped portion, where the large diameter portion of the gear shaft contacts the inner race of the second bearing, and the stepped portion of the rotor shaft has a clearance larger than the internal clearance of the second bearing with respect to the third bearing. This configuration reduces the transmission of thrust force to the third casing member, thereby minimizing NV.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the rotor shaft is rotatably held by the third casing member through a third bearing, then the rotor shaft is supported at both ends, but the thrust force is transmitted to the third casing member causing noise and vibration
Solution Approach 1:
The harmful thrust force transmission path to the third casing member is extracted and eliminated by designing the stepped portion to contact the gear shaft's large diameter portion, isolating the third bearing from thrust force
Solution Approach 2:
The large diameter portion of the gear shaft acts as an intermediary element that absorbs and redirects the thrust force to the second bearing, preventing it from reaching the third casing member through the third bearing
2Object-generated harmful factors
If the internal clearance of the second bearing is reduced to suppress thrust force transmission, then noise and vibration are reduced, but the manufacturing precision and assembly difficulty increase
Solution Approach 1:
The thrust force transmission path through the second bearing's internal clearance is extracted and replaced by the direct contact path through the stepped portion and large diameter portion
Solution Approach 2:
The design changes the clearance parameter from a tight tolerance requirement to a larger, more manufacturable clearance by redirecting the thrust force through the stepped portion contact
Data Source
AI summary
An electric vehicle in which a gear shaft provided with a helical gear is held by a first casing member through a first bearing. The gear shaft has a splined outer circumferential surface fitted in a splined inner circumferential surface of a rotor shaft that is held by a second casing member through a second bearing and is held by a third casing member through a third bearing. The gear shaft includes a large diameter portion which has a diameter larger than a diameter of the splined outer circumferential surface, and the large diameter portion is in contact, at its end surface, with an end surface of an inner race of the second bearing. The rotor shaft includes a stepped portion that is spaced apart from the third bearing by a clearance that is larger than an internal clearance of the second bearing.