Planetary Gear Train for Automatic Transmission
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Solution Overview
Problem
Current automatic transmissions with increased shift stages face challenges in installability, power flow efficiency, and production cost due to the need for more parts, and often suffer from suboptimal gear ratio spans, which affect fuel consumption and drivability.
Innovation Solution
A planetary gear train configuration for automatic transmissions that includes four planetary gear sets, two external gears, and six control elements, arranged in a manner that reduces length and improves installability, while achieving at least nine forward speeds and one reverse speed, with a wide range of gear teeth for optimal gear ratios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the number of planetary gear sets and control elements is increased to achieve more shift stages, then the number of forward speeds and reverse speeds increases, but the length of the transmission increases and installability deteriorates
Solution Approach 1:
The patent employs nested planetary gear sets where smaller planetary gears are positioned within the space of larger planetary gear sets. Specifically, the third and fourth planetary gear sets are arranged concentrically with the first and second planetary gear sets, allowing multiple gear stages to be compacted into a shorter axial length while maintaining 9 forward speeds and 1 reverse speed
Solution Approach 2:
The patent transitions from a linear arrangement of planetary gear sets to a multi-dimensional compact layout. By arranging gear sets in parallel shafts (input shaft and output shaft) and using concentric nesting, the transmission achieves high gear ratios in a reduced axial length, effectively utilizing radial and concentric space rather than only linear extension
2Adaptability or versatility
If the number of planetary gear sets is increased to achieve more shift stages, then the number of forward speeds and reverse speeds increases, but the number of parts increases and production cost increases
Solution Approach 1:
The patent designs planetary gear sets and control elements that serve multiple functions. The same planetary gear sets are used to generate both forward speeds and reverse speeds, and control elements (clutches and brakes) are strategically positioned to control multiple gear stages. This multi-functionality reduces the total number of parts needed compared to conventional designs that require separate gear sets for each speed stage
Solution Approach 2:
The patent merges the functionality of multiple planetary gear sets into a compact four-set configuration that achieves 9 forward speeds and 1 reverse speed. By combining control elements and optimizing the arrangement of planetary gears, the design reduces part count while maintaining complex gear ratio capabilities, thereby lowering production cost and assembly complexity
3Adaptability or versatility
If conventional planetary gear arrangements are used to achieve more shift stages, then the number of forward speeds increases, but power flow efficiency deteriorates
Solution Approach 1:
The patent optimizes the local arrangement of planetary gear sets and control elements to minimize power loss. Each planetary gear set is positioned and sized to optimize power flow for specific speed ranges, and control elements are placed to minimize engagement time and reduce energy loss during shifting. This localized optimization maintains high power flow efficiency across all 9 forward speeds
Data Source
AI summary
A planetary gear train of an automatic transmission for a vehicle may include a first planetary gear set, a second planetary gear set, a third planetary gear set, a fourth planetary gear set, an input shaft mounted with the first and second planetary gear sets at an external circumference of the input shaft, an output shaft disposed in parallel with the input shaft and mounted with the third and fourth planetary gear sets on an external circumference of the output shaft, a first shaft, a second shaft, a third shaft directly connected with the input shaft, a fourth shaft, a fifth shaft, a sixth shaft gear-meshed with the fourth shaft, a seventh shaft engaged with the third shaft selectively, an eighth shaft directly connected with the output shaft, a ninth shaft, and transfer gears each gear-meshed with at least one of the shafts.