Planetary Gear Train for Linear Step Ratios
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Solution Overview
Problem
Current automatic transmissions with 8-speeds have limited fuel efficiency due to increased internal components, manufacturing costs, and deteriorated power transmission efficiency, and fail to achieve linear step ratios and sufficient gear ratio spans for improved drivability and engine efficiency.
Innovation Solution
A planetary gear train for automatic transmissions that uses a minimum number of components to achieve at least nine forward speed stages and one reverse speed stage by combining four simple planetary gear sets with six friction elements, allowing for linear increase or decrease of step ratios and expanding gear ratio spans.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the number of gear shift stages is increased to improve fuel efficiency, then fuel efficiency is improved, but the number of internal components increases leading to difficult mounting, increased manufacturing cost and weight, and deteriorated power transmission efficiency
Solution Approach 1:
The patent combines multiple planetary gear sets (first, second, third, and fourth planetary gear sets) into a single integrated transmission system where rotation elements from different gear sets are connected together. This merging approach enables the system to achieve 9-speed operation with fewer independent components compared to traditional multi-gear transmissions, resolving the contradiction between increased gear stages and component complexity
Solution Approach 2:
Rotation elements serve multiple functions across different planetary gear sets. For example, the sixth rotation element is continuously connected to both the second planetary gear set and serves as a connection point for the third planetary gear set. This multi-functionality allows a single component to participate in multiple gear ratio formations, reducing the total number of components needed while maintaining 9-speed capability
2Use of energy by moving object
If the span of gear ratios is increased to improve fuel efficiency, then fuel efficiency is improved, but step ratios between speed stages cannot be increased or decreased linearly deteriorating engine driving efficiency and drivability
Solution Approach 1:
The patent achieves a gear ratio span of 9.5 or more while maintaining linear step ratios between speed stages by carefully selecting and configuring the tooth counts of gears within the planetary gear sets. The parameter optimization allows the transmission to provide both wide ratio spread for fuel efficiency and linear progression for smooth shifting and drivability
Solution Approach 2:
The transmission system dynamically adjusts through 9 different forward speed stages and 1 reverse speed stage, allowing the vehicle to operate optimally across a wide range of driving conditions. The ability to select from multiple gear ratios enables the system to maintain engine operating efficiency while providing smooth, linear transitions that preserve drivability
3Ease of manufacture
If a minimum number of components is used to achieve multiple speed stages, then manufacturing cost and weight are reduced, but the ability to achieve linear step ratios and sufficient gear ratio spans is limited
Solution Approach 1:
The planetary gear sets are nested along a common transmission axis, with each gear set containing sun gears, planet gears, and ring gears that are concentrically arranged. This nested configuration maximizes the gear ratio capabilities within a compact structure, achieving 9-speed operation with minimal components while maintaining sufficient gear ratio span for both fuel efficiency and drivability
Data Source
AI summary
A planetary gear train of an automatic transmission for a vehicle may include an input shaft receiving torque of an engine, an output shaft outputting changed torque of the engine, 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, and six friction elements disposed to selectively connect the rotation elements, or to selectively connect at least one rotation element and a transmission housing.