Planetary Gear Train Layout for Compact 8-Speed Transmission
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current eight-speed automatic transmissions face challenges in achieving improved fuel efficiency and installability due to increased complexity and weight, with limited gear ratio span and deteriorated shift feel, particularly with the use of multiple planetary gear sets and control elements.
Innovation Solution
A planetary gear train configuration utilizing four planetary gear sets, two external gears, and five control elements, arranged in a parallel layout to reduce length and complexity, allowing for at least eight forward speeds and one reverse speed, with a wide range of gear teeth variations to optimize gear ratios and improve power delivery and fuel efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the number of planetary gear sets and control elements is increased to achieve more shift stages, then fuel efficiency is improved, but device complexity and total length increase, deteriorating installability
Solution Approach 1:
The patent combines multiple planetary gear sets (first, second, third, and fourth planetary gear sets) into a single integrated transmission assembly, where rotational elements from different planetary gear sets are coupled together. This merging approach achieves 8 or more shift stages without proportionally increasing the number of independent components, as some control elements serve multiple gear sets simultaneously.
Solution Approach 2:
Control elements in the patent are designed to control multiple planetary gear sets simultaneously. For example, a single control element may control both the first and second planetary gear sets, making it multi-functional. This reduces the total number of control elements needed compared to traditional designs where each planetary gear set requires separate control elements.
2Use of energy by moving object
If the number of planetary gear sets and control elements is increased to achieve more shift stages, then fuel efficiency is improved, but the total length of the transmission increases, deteriorating installability
Solution Approach 1:
The patent arranges planetary gear sets in a nested configuration where rotational elements of one planetary gear set are coupled with rotational elements of adjacent planetary gear sets. The first, second, and third planetary gear sets are arranged along the input shaft, with the fourth planetary gear set connected to the output shaft, creating a compact nested structure that minimizes the overall length of the transmission assembly.
Solution Approach 2:
The patent transitions from a linear arrangement of planetary gear sets to a multi-dimensional configuration where gear sets are distributed across different shafts (input shaft and output shaft) and interconnected through various rotational elements. This spatial redistribution reduces the length in any single dimension while maintaining the required number of shift stages.
3Device complexity
If dog clutches are used instead of wet-type control elements, then device complexity is reduced, but shift feel deteriorates
Solution Approach 1:
The patent employs wet-type control elements (clutches and brakes) that use friction-based engagement rather than mechanical dog clutches. These control elements are designed to provide smooth, progressive engagement through hydraulic pressure control, sacrificing some mechanical simplicity to achieve superior shift quality and driver comfort.
4Length of moving object
If a compact arrangement of planetary gear sets is used, then installability is improved, but gear ratio span is limited
Solution Approach 1:
The patent varies the number of teeth on planetary gears and the configuration of rotational elements across different planetary gear sets to achieve a wide gear ratio span (6.5 or more) within a compact structure. By optimizing gear tooth counts and arrangement, the transmission achieves both compactness and extended gear ratio range.
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 enhances power delivery performance, reduces fuel consumption, improves installability, and achieves a gear ratio span of over 8.9, while maintaining efficient shift stage linearity and reducing material costs by minimizing non-controlled control elements and drag torque.
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
Data Source
AI summary
A planetary gear train of an automatic transmission for a vehicle may include: first to fourth planetary gear sets respectively having first to third rotational elements, fourth to sixth rotational elements, seventh to ninth rotational elements, tenth to twelfth rotational elements; an input shaft mounted with the first, second, and third planetary gear sets; an output shaft mounted with the fourth planetary gear set; first to ninth shafts; three clutches and two brakes as control elements; and two transfer gears. In particular, the first shaft fixedly connects the first and sixth rotational elements, the fourth shaft fixedly connects the fourth and ninth rotational elements and is selectively connected with the second shaft, the seventh shaft fixedly connects the tenth rotational element and externally gear-meshes with the fifth shaft, and the eighth shaft fixedly connects the eleventh rotational element and selectively externally gear-meshes with the sixth shaft.