Parallel Planetary Gear Train for 8-Speed Transmission Mountability
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Solution Overview
Problem
Existing planetary gear trains face challenges in achieving a high number of shift speeds while maintaining mountability, cost-effectiveness, and power delivery efficiency, particularly in front-wheel drive vehicles, as the increase in components complicates assembly and affects fuel economy.
Innovation Solution
A planetary gear train design featuring two planetary gear sets disposed in parallel on the input and output shafts, connected by externally-meshed gears and six frictional elements, allowing for eight forward speeds and one reverse speed, with optimized gear ratios achieved through the operation of clutches and brakes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the number of shift speeds is increased, then the fuel mileage and performance are improved, but the number of components increases leading to deteriorated mountability, cost, weight and power delivery efficiency
Solution Approach 1:
The transmission system is divided into two separate planetary gear sets (first planetary gear set on input shaft, second planetary gear set on output shaft) that operate independently but are connected through transfer gears. This segmentation allows each gear set to contribute to multiple speed ratios without requiring all components to be present simultaneously, reducing overall component complexity while achieving 8 forward speeds and 1 reverse speed
Solution Approach 2:
The planetary gear sets are designed with multi-functionality where the same basic structure (sun gear, planet carrier, ring gear) can achieve different speed ratios by selectively engaging different friction elements (clutches and brakes) on different rotation elements. This allows a single planetary gear set design to serve multiple speed ratios, reducing the need for additional specialized components
2Productivity
If the number of shift speeds is increased, then the performance is improved, but the mountability is deteriorated
Solution Approach 1:
The patent transitions from a traditional single-line planetary gear arrangement to a two-dimensional parallel shaft configuration. The first planetary gear set is disposed on the input shaft and the second planetary gear set is disposed on the output shaft, with both shafts rotating in parallel. This spatial reorganization reduces the axial length of the gear train while maintaining the capability for multiple speed ratios
3Productivity
If the number of shift speeds is increased, then the fuel economy is improved, but the power delivery efficiency is deteriorated
Solution Approach 1:
The patent extracts and eliminates unnecessary intermediate components and friction elements that would cause power loss through additional engagement points. By using only two friction elements per planetary gear set and directly connecting critical rotation elements to the input and output shafts, the design minimizes the number of power transmission stages and associated energy losses while still achieving 8 forward speeds and 1 reverse speed
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 design enhances mountability, reduces component count, and improves power delivery and fuel economy by enabling efficient gear ratio changes, thus addressing the limitations of traditional gear trains.
Implementation Method 1
six frictional elements including four clutches selectively connecting the first, second, fourth, and sixth rotation elements to the input shaft and two brakes selectively connecting the first and second rotation elements to the transmission housing respectively
Implementation Method 2
three transfer gears meshing externally the fourth, fifth, and sixth rotation elements of the second planetary gear set with the input shaft and the first and third rotation elements
Data Source
AI summary
A planetary gear train may include input shaft, output shaft, first planetary gear set disposed on the input shaft and including first rotation element selectively connected to the input shaft or transmission housing, second rotation element selectively connected to the input shaft or the transmission housing, and third rotation element connected to the output shaft, second planetary gear set disposed on the output shaft and including fourth rotation element selectively connected to the input shaft and connected to the first rotation element, fifth rotation element connected to the third rotation element and directly connected to the output shaft, and sixth rotation element selectively connected to the input shaft, three transfer gears, and six frictional elements including four clutches selectively connecting the first, second, fourth, and sixth rotation elements to the input shaft and two brakes selectively connecting the first and second rotation elements to the transmission housing respectively.