Vehicle Shaft Assembly Layout for Fewer Bearings and Axis Alignment
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Solution Overview
Problem
Existing power transmission devices for vehicles have a high number of bearings, leading to increased weight and energy loss, which can be mitigated by reducing the number of bearings while maintaining axis alignment and reducing weight.
Innovation Solution
A power transmission device with a shaft assembly comprising an electric-motor rotor shaft and a gear shaft, connected through a spline engagement portion, a fitting portion, and a damper portion, with a bearing positioned to overlap with the connection portion in the radial direction, reducing the diameter of the rotor shaft and thereby minimizing weight and energy loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the number of bearings is reduced from four to three, then energy loss is reduced, but axis alignment between rotor shaft and gear shaft deteriorates
Solution Approach 1:
A fitting portion is introduced as an intermediary element between the spline engagement portion and the damper portion. This fitting portion acts as a mediator that maintains axis alignment between the rotor shaft and gear shaft while allowing the reduction of bearing count from four to three, thereby resolving the contradiction between energy loss reduction and manufacturing precision maintenance
Solution Approach 2:
The connection portion is segmented into three distinct functional sections: spline engagement portion (for torque transmission), fitting portion (for axis alignment), and damper portion (for vibration isolation). This segmentation allows each section to perform its specific function independently, enabling the reduction of bearing count while maintaining overall system precision
2Manufacturing precision
If the outside diameter of the gear shaft in the fitting portion is increased to maintain axis alignment, then axis alignment is improved, but the outside diameter of the rotor shaft must be increased, leading to increased weight
Solution Approach 1:
The fitting portion merges the functions of alignment and support into a single integrated structure. By combining the alignment function with the existing shaft structure rather than adding separate alignment components, the design achieves precise axis alignment without increasing the rotor shaft diameter, thereby avoiding weight increase
Solution Approach 2:
The fitting portion provides localized quality enhancement at the specific location where axis alignment is needed. Instead of uniformly increasing the diameter of the entire rotor shaft, the design applies the fitting portion only at the critical connection region, maintaining local precision without global weight increase
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 proposed configuration reduces the number of bearings from four to three, minimizing energy loss and weight increase, while maintaining effective axis alignment and reducing the overall length of the drive unit.
Implementation Method 1
a damper portion in which an elastic member is disposed between the outer circumferential surface of the gear shaft and the inner circumferential surface of the rotor shaft
Data Source
AI summary
A vehicle power transmission device includes a shaft assembly constituted by an electric-motor rotor shaft and a gear shaft. The shaft assembly includes a connection portion in an end portion of the gear shaft is introduced in an end portion of the rotor shaft. The connection portion includes a spline engagement portion, a fitting portion and a damper portion in which an elastic member is disposed between an outer circumferential surface of the gear shaft and an inner circumferential surface of the rotor shaft. The spline engagement portion, the fitting portion and the damper portion are arranged in this order as viewed in a direction away from another end portion of the rotor shaft toward another end portion of the gear shaft. A bearing supporting the shaft assembly is located in a position that overlaps with the connection portion as viewed in a radial direction of the shaft assembly.