Compound Planetary Gear Train for 8-Speed Automatic Transmission
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Solution Overview
Problem
Existing planetary gear trains in automatic transmissions face challenges in achieving a high number of shift speeds while minimizing components, which can lead to deteriorated mountability, cost, weight, and power delivery efficiency, especially in front wheel drive vehicles.
Innovation Solution
A planetary gear train design that includes a compound planetary gear set on the output shaft connected to the input shaft through externally-meshed gears, utilizing a combination of clutches and brakes to achieve eight forward speeds and two reverse speeds, allowing for optimal gear ratio setting and improved power delivery and fuel economy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the number of shift speeds is increased, then speed ratios can be more optimally designed and fuel economy is improved, but the number of components increases leading to deteriorated mountability, cost, weight and power delivery efficiency
Solution Approach 1:
The patent combines multiple planetary gear sets into a compound planetary gear set where rotation elements are shared. Specifically, the first planetary gear set and second planetary gear set share a common ring gear and planet carrier, merging what would traditionally be separate components into a unified structure. This allows achieving 8 forward speeds and 2 reverse speeds with fewer total components, resolving the contradiction between increased shift speeds and component quantity.
Solution Approach 2:
The compound planetary gear set design enables rotation elements to serve multiple functions across different gear ratios and operating modes. The shared ring gear and planet carrier participate in multiple gear train configurations, allowing a single component to contribute to multiple speed ratios. This multi-functionality reduces the total component count while maintaining the capability for 8 forward speeds and 2 reverse speeds.
2Adaptability or versatility
If the number of shift speeds is increased, then speed ratios can be more optimally designed, but mountability is deteriorated especially in front wheel drive vehicles
Solution Approach 1:
By merging multiple planetary gear sets into a compound structure with shared rotation elements, the patent reduces the overall size and component count of the transmission system. This compact configuration improves mountability in front wheel drive vehicles while maintaining the versatility of 8 forward speeds and 2 reverse speeds through the integrated gear train design.
3Adaptability or versatility
If the number of shift speeds is increased, then speed ratios can be more optimally designed, but power delivery efficiency is deteriorated
Solution Approach 1:
The compound planetary gear set with shared rotation elements reduces the number of gear meshing interfaces and friction elements required. By consolidating the gear train structure, the patent minimizes energy losses at each transmission stage, improving overall power delivery efficiency while maintaining 8 forward speeds and 2 reverse speeds.
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 design enhances mountability, power delivery performance, and fuel economy by reducing the number of components and enabling easier gear ratio changes, while also improving reverse speed performance.
Implementation Method 1
connecting rotation elements of the compound planetary gear set to an input shaft through a plurality of externally-meshed gears
Implementation Method 2
friction elements including clutches selectively connecting the first, second, and fourth rotation elements to the input shaft, and brakes selectively connecting the first and second rotation elements to a transmission housing
Data Source
AI summary
A planetary gear train of an automatic transmission may include an input shaft, an output shaft, a compound planetary gear set disposed on the output shaft, and including a first rotation element selectively connected to the input shaft through two paths respectively having an externally-meshed gear and operated as a selective fixed element, a second rotation element selectively connected to the input shaft through one path having an externally-meshed gear and operated as a selective fixed element, a third rotation element connected to the output shaft, and a fourth rotation element selectively connected to the input shaft through one path having an externally-meshed gear, three transfer gears forming the externally-meshed gears, and friction elements provided with clutches selectively connecting the first, second, and fourth rotation elements to the input shaft and brakes selectively connecting the first and second rotation elements to a transmission housing.