Planetary Gear Train with Shared Ring Gears for Wide Ratio Span
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Solution Overview
Problem
Conventional 8-speed automatic transmissions face limitations in achieving optimal power performance and fuel economy due to a narrow gear ratio span, which affects the linearity of step ratios and drivability.
Innovation Solution
A planetary gear train with four simple planetary gear sets and seven control elements, including clutches and brakes, is designed to achieve at least eleven forward speed stages and one reverse speed stage, widening the gear ratio span and securing linearity of step ratios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the number of speed stages is increased to enhance fuel economy and optimize drivability, then power performance and driving efficiency are improved, but the number of internal components increases leading to deteriorated mountability, cost, weight, and transmission efficiency
Solution Approach 1:
The patent merges multiple planetary gear sets into a integrated structure where gear sets share common components. Specifically, the first and second planetary gear sets share a common ring gear, and the third and fourth planetary gear sets share another common ring gear, reducing the total number of independent components while maintaining multiple speed stages
Solution Approach 2:
Individual components perform multiple functions across different speed stages. The shared ring gears serve multiple gear sets simultaneously, and control elements (clutches and brakes) are strategically positioned to control multiple gear sets, enabling a single component to fulfill multiple operational roles across various transmission ratios
2Use of energy by moving object
If conventional 8-speed automatic transmission is used, then some fuel economy improvement is achieved, but the gear ratio span is narrow (6.5-7.5) resulting in poor linearity of step ratios and inadequate power performance
Solution Approach 1:
The patent fundamentally changes the gear ratio parameters by implementing a wide gear ratio span of 9.0 or more, which is significantly larger than conventional 8-speed transmissions (6.5-7.5). This parameter change enables better linearity of step ratios and improved adaptability across different driving conditions while maintaining fuel economy benefits
3Adaptability or versatility
If the gear ratio span is increased to improve power performance and fuel economy, then linearity of step ratios is improved, but the transmission structure becomes more complex
Solution Approach 1:
The patent employs a nested arrangement where planetary gear sets are positioned concentrically around a common input shaft, with sun gears, planet carriers, and ring gears nested within each other. This nesting allows multiple gear sets to occupy compact space while achieving the required wide gear ratio span and improved step ratio linearity
Data Source
AI summary
The present disclosure provides a planetary gear train of an automatic transmission for a vehicle. The planetary gear train may include: an input shaft receiving torque of an engine; an output shaft outputting changed torque; a first planetary gear set including first, second, and third rotation elements; a second planetary gear set including fourth, fifth, and sixth rotation elements; a third planetary gear set including seventh, eighth, and ninth rotation elements; a fourth planetary gear set including tenth, eleventh, and twelfth rotation elements. The planetary gear train improves power delivery performance and fuel economy by achieving at least eleven forward speed stages and widening speed ratio (or gear ratio) with a reduced number of constituent elements being used, and secures linearity of step ratios.