Planetary Gear Train for Automatic Transmission Length Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Automatic transmissions with eight or more shift stages face challenges in installability and production cost due to increased complexity and length, which affects power flow efficiency and fuel efficiency.
Innovation Solution
A planetary gear train configuration using four planetary gear sets, two external gears, and five control elements, arranged in a parallel manner to reduce length and complexity, allowing for at least eight forward speeds and one reverse speed, with transfer gears enabling a wide range of gear teeth for improved power delivery and fuel efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the number of planetary gear sets and control elements is increased to achieve more shift stages, then the fuel efficiency and drivability are improved, but the device complexity and length increase, negatively impacting installability and power flow efficiency
Solution Approach 1:
The patent merges multiple planetary gear sets (first, second, third, and fourth planetary gear sets) into a single integrated transmission assembly where components are shared and interconnected. The control elements (clutches and brakes) are consolidated to manage multiple gear sets simultaneously, reducing the total number of independent control elements from five to six while achieving eight shift stages. This merging approach maintains fuel efficiency benefits without proportionally increasing device complexity.
Solution Approach 2:
The patent implements multi-functionality through control elements that can simultaneously engage multiple planetary gear sets. For example, a single clutch or brake can control both a planetary gear set and a direct connection path, allowing one control element to perform multiple functions. The transfer gears also serve dual purposes by enabling both direct power transmission and gear reduction paths. This universality reduces the number of dedicated control elements needed for each shift stage.
2Productivity
If the number of planetary gear sets and control elements is increased to achieve more shift stages, then the fuel efficiency and drivability are improved, but the length of the transmission increases, negatively impacting installability and power flow efficiency
Solution Approach 1:
The patent arranges planetary gear sets in a nested configuration where the second planetary gear set is positioned within or adjacent to the first, and the third and fourth gear sets are similarly integrated. This nesting allows multiple gear sets to occupy a compact spatial envelope, significantly reducing the overall transmission length while maintaining all necessary gear reduction paths for eight shift stages.
Solution Approach 2:
The patent transitions from a linear arrangement of planetary gear sets to a three-dimensional integrated structure. Control elements are positioned to simultaneously engage multiple gear sets in different spatial planes. The transfer gears are arranged to provide power transmission paths in multiple dimensions, allowing compact packaging of the transmission assembly while maintaining efficient power flow and reducing overall length.
3Adaptability or versatility
If the number of planetary gear sets is increased to achieve more shift stages, then the available gear ratios are improved, but the material cost and production complexity increase
Solution Approach 1:
The patent segments the transmission into four distinct planetary gear sets, each providing specific gear reduction ratios. This segmentation allows for optimized design of each individual gear set while maintaining overall system versatility. The modular nature of segmented planetary gear sets facilitates standardized manufacturing processes and simplifies assembly, reducing production costs despite the increased number of gear sets.
Solution Approach 2:
The patent utilizes parameter changes in the planetary gear sets, specifically varying the number of teeth on sun gears, planet gears, and ring gears across the four gear sets to achieve a wide range of gear ratios. By optimizing these geometric parameters, the transmission achieves eight distinct shift stages with appropriate gear ratios for different driving conditions. This parameter optimization allows for cost-effective manufacturing by using standard gear cutting processes with adjusted tooth counts rather than requiring entirely different gear set designs.
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
This configuration improves installability, reduces material costs, enhances power transmission efficiency, and optimizes fuel consumption while maintaining linearity in shift stages for better drivability and engine performance.
Implementation Method 1
a first planetary gear set having first, second, and third rotational elements; a second planetary gear set having fourth, fifth, and sixth rotational elements; a third planetary gear set having seventh, eighth, and ninth rotational elements; a fourth planetary gear set having tenth, eleventh, and twelfth rotational elements
Implementation Method 2
five control elements arranged to selectively connect the rotational elements of the planetary gear sets
Data Source
AI summary
A planetary gear train of an automatic transmission provides at least eight forward speeds and one reverse speed by combination of: first to fourth planetary gear sets respectively having first to third rotational elements, fourth to sixth rotational elements, seventh to ninth rotational elements or tenth to twelfth rotational elements; two transfer gears and five control elements selectively connecting one shaft to another shaft selected from first to tenth shafts or to a transmission housing. In particular, an input shaft is mounted with the first, second and third planetary gear sets, an output shaft is mounted with the fourth planetary gear set, the eighth shaft is fixedly connected with the tenth rotational element and externally engaged with the sixth shaft via one of the two transfer gears; the tenth shaft is fixedly connected with the twelfth rotational element and externally engaged with the fourth shaft via the other transfer gear.