Compact Differential Device with Variable Thickness Cover
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Solution Overview
Problem
Conventional differential devices are structurally wide in the axial direction, making them difficult to incorporate into transmission systems with layout restrictions, and reducing their thickness to alleviate this issue compromises meshing accuracy and stability.
Innovation Solution
The differential device features side gears with annular toothing and a cover portion with a plate-shaped side wall that supports the side gears, allowing for a larger diameter and more teeth on the side gears while maintaining structural rigidity, and the use of washers to enhance support strength without increasing axial dimension.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the thickness of the cover portions is reduced to flatten the differential device in the axial direction, then the axial width is reduced, but the cover portions become structurally weak and prone to tilting which deteriorates meshing accuracy
Solution Approach 1:
The cover portion is designed with non-uniform thickness: the first region (peripheral area) has a first thickness while the second region (central area) has a greater second thickness. This local quality variation allows the cover to maintain sufficient structural rigidity and support the side gear without tilting, while still achieving an overall reduced axial width. The thicker central region specifically prevents the cover from tilting under load, thereby maintaining meshing accuracy.
2Strength
If the diameter of side gears is increased to have more teeth than pinions, then the torque transmission capability is improved, but the axial width of the differential device increases
Solution Approach 1:
Instead of increasing the axial width to accommodate larger side gear diameter, the invention utilizes the radial dimension by positioning the side gear to extend radially from the input shaft. The cover portion is configured to cover the side gear from the axial direction, allowing the side gear to have sufficient diameter for adequate tooth count and torque transmission while keeping the axial width compact through the variable thickness design.
3Stability of the object's composition
If the cover portions are made thick to prevent tilting and maintain meshing accuracy, then the structural stability is improved, but the axial width of the differential device increases
Solution Approach 1:
The cover portion employs local quality variation with different thicknesses in different regions. The second region (central area) has greater thickness to provide the necessary structural stability and prevent tilting under load, while the first region (peripheral area) has reduced thickness to minimize the overall axial width. This localized thickening only where structurally necessary achieves both stability and compactness.
4Length of moving object
If the intermediate wall portions are made thin to reduce axial width, then the compactness is improved, but the support strength for the toothing portions is reduced
Solution Approach 1:
The cover portion and intermediate wall portion are designed to work together as an integrated support structure. The cover portion's variable thickness design compensates for the reduced thickness of the intermediate wall portions. The thicker second region of the cover provides additional support to the thin intermediate wall portions, maintaining adequate support strength for the toothing portions while achieving compact axial width through the combined structure.
Data Source
AI summary
In a differential device, side gears include: shaft portions; and intermediate wall portions each formed in a flat ring plate shape orthogonal to an axis of output shafts and integrally connecting between the shaft portions and toothing portions separated outward from the shaft portions in a radial direction of an input member, respectively. At least part of each intermediate wall portion is formed as a thin portion having an outside surface retreating axially inward from a backside of the tooting portion. A side wall portion of a cover portion integrally includes an outer-periphery-side side wall portion having an inside surface facing the backside of the toothing portion, and an inner-periphery-side side wall portion having an inside surface facing a backside of the intermediate wall portion. At least part of the inner-periphery-side side wall portion is formed thicker than the outer-periphery-side side wall portion and protrudes toward the thin portion.