Nested Planetary Gear CVT Axial Length Reduction
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Solution Overview
Problem
Existing continuously variable transmissions (CVTs) with planetary gear mechanisms have a large axial length due to the separation of pinions along the axial direction, leading to increased bearing load, reduced precision, and shorter bearing life, which complicates the arrangement and reliability of the transmission.
Innovation Solution
A CVT design incorporating a dual planetary gear mechanism in the reversing gear system, featuring a 2-train/4-element planetary gear configuration, which allows for a shorter axial arrangement, larger bearing diameter, reduced pinion weight, and improved support precision by reducing flexing and load fluctuations, enabling a more compact and reliable transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If pinions are separated along the axial direction in the planetary gear mechanism, then the transmission can achieve multiple gear ratios, but the axial length of the transmission increases
Solution Approach 1:
The patent employs a nested planetary gear structure where multiple pinions (P1, P2, P3) are arranged concentrically around a shared sun gear (S1) rather than being separated axially. The pinions engage with different sun gears (S1, S2, S3) in a nested configuration, allowing multiple gear ratios to be achieved within a compact radial space, thereby reducing the axial length while maintaining adaptability.
Solution Approach 2:
The invention transitions from an axial arrangement of pinions to a radial arrangement. By organizing the planetary gears in the radial dimension rather than the axial dimension, the patent achieves multiple gear ratios without increasing the axial length, effectively using another spatial dimension to resolve the contradiction.
2Adaptability or versatility
If pinions are separated along the axial direction, then gear ratio changes are possible, but bearing diameter must be reduced and precision deteriorates
Solution Approach 1:
The nested configuration allows all pinions to share a common bearing support structure at the center of the planetary mechanism. This centralized support enables the use of a larger diameter bearing that can accommodate all pinions, thereby maintaining high support precision while still achieving gear ratio variability through the nested engagement of pinions with different sun gears.
3Adaptability or versatility
If pinions are separated axially, then multiple gear ratios are achieved, but bearing load increases and life decreases
Solution Approach 1:
The nested planetary gear arrangement concentrates the load paths through a centralized bearing support structure. This allows for a larger bearing diameter that can handle the combined loads from all pinions more effectively, distributing the load more evenly and reducing stress concentrations, thereby extending bearing life while maintaining gear ratio versatility.
4Reliability
If a conventional planetary gear mechanism with three pinions is used, then the transmission functions properly, but the axial length becomes large
Solution Approach 1:
The patent implements a nested planetary gear mechanism where three pinions (P1, P2, P3) are arranged concentrically around a shared sun gear (S1) and engage with different sun gears (S1, S2, S3) in a nested fashion. This nested configuration maintains the transmission's functionality and reliability by providing multiple gear ratios, while simultaneously reducing the axial length by eliminating the need for axial separation of pinions.
Data Source
AI summary
In a continuously variable transmission (“CVT”) using a toroidal-race continuously variable ratio device and a planetary gear mechanism, the rotation of the input shaft (12) is directly transmitted to the carrier C of the planetary gear mechanism (61), and rotation resulting from gearing and reversal by the variator (5) is transmitted to the sun gear (S1). When the low clutch L is engaged, the rotation of the ring gear (R3) is transmitted via the reversing gear mechanism (71) to the output shaft (13), and when the high clutch H is engaged, the rotation of the sun gear (S2) is transmitted to the output shaft (13).