Two-Stage Planetary Gear Compact Transfer Case Design
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Solution Overview
Problem
Two-stage transfer cases in countershaft construction require significant installation space, making them unsuitable for applications with limited space, while planetary designs face high switching forces due to the mass of the planetary carrier and gears, leading to delayed shifting operations.
Innovation Solution
A two-stage planetary drive assembly where only a lightweight shift sleeve is axially displaced to change gears, eliminating the need to shift the planetary carrier and gears, allowing for a compact design and reduced switching forces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a two-stage transfer case is designed in countershaft construction, then it is inexpensive and technically simple, but it requires a comparatively large amount of installation space axially
Solution Approach 1:
The patent inverts the conventional planetary gear arrangement by making the planetary carrier the stationary element and the sun gear rotatable, rather than the typical configuration. This inversion allows for a more compact axial design while maintaining the benefits of planetary gear construction, resolving the contradiction between manufacturing simplicity and compact axial dimensions.
Solution Approach 2:
The transfer case employs a nested arrangement where the planetary gears are positioned within the sun gear structure, and the shift sleeve is integrated into the planetary carrier assembly. This nesting reduces the overall axial length while maintaining all necessary functional components, addressing the space constraint issue.
2Length of moving object
If a planetary transfer gear is designed with a planetary carrier and planetary gears, then it achieves compact axial design, but a comparatively large mass has to be shifted during shifting operations
Solution Approach 1:
The patent extracts the shifting function from the heavy planetary carrier and planetary gears, concentrating it instead in a lightweight shift sleeve. The shift sleeve selectively engages or disengages connections between the sun gear and planetary carrier, allowing gear changes without moving the massive planetary components. This extraction dramatically reduces the mass that must be accelerated during shifting while preserving the compact axial design.
3Adaptability or versatility
If the planetary carrier with planetary gears is shifted during gear changing, then gear ratios are changed, but high switching forces are required and switching processes are delayed
Solution Approach 1:
The shift sleeve acts as an intermediary element that mediates gear ratio changes without requiring direct movement of the planetary carrier. By engaging or disengaging the shift sleeve, the connection between the sun gear and planetary carrier is selectively established or broken, enabling gear ratio changes through low-force sleeve displacement rather than high-force carrier movement.
Data Source
Figure 1
AI summary
The invention relates to a two-stage planetary drive (2) for a transfer case (1) of a motor vehicle, comprising an input shaft (12), a planet carrier (5) with planet gears (8, 8'), a ring gear (6), a sun gear (7), and an axially displaceable shift sleeve (16), wherein the planetary drive (2) is arranged concentrically within a drive gear (5'). The planetary drive (2) according to the invention is characterized in that the shift sleeve (16) is rotationally fixed to the input shaft (12), wherein in a first end position the shift sleeve (16) is rotationally fixed to the sun gear (7), and in a second end position the input shaft (12) is rotationally fixed to the planet carrier (5). The invention further relates to a corresponding transfer case (1).