Planetary Gear Train for Nine-Speed Automatic Transmission
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Solution Overview
Problem
Existing automatic transmissions with multiple shift stages face challenges in installability, production cost, weight, and power flow efficiency due to increased number of planetary gear sets, which also deteriorate shift feel and fuel consumption.
Innovation Solution
A planetary gear train with four simple planetary gear sets and six control elements, including clutches and brakes, is designed to achieve nine forward speeds and one reverse speed, reducing the number of parts and improving power delivery and fuel efficiency by optimizing torque flow through a combination of shafts and control elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the number of planetary gear sets is increased to achieve more shift stages, then fuel consumption and driving efficiency are improved, but device complexity, weight, and installability deteriorate
Solution Approach 1:
The patent merges multiple planetary gear sets into a integrated structure where four planetary gear sets (first through fourth) share common shafts and control elements. The first and fourth planetary gear sets share the first shaft, while the second and third planetary gear sets share the fourth shaft, creating a consolidated transmission system that achieves nine forward speeds without proportionally increasing part count
Solution Approach 2:
Control elements such as the first clutch, second clutch, third clutch, fourth clutch, fifth brake, and sixth brake serve multiple functions across different planetary gear sets. For example, the first clutch selectively connects rotational elements from both the first and fourth planetary gear sets, enabling a single control element to manage torque flow through multiple gear sets simultaneously
2Productivity
If the number of planetary gear sets is increased to achieve more shift stages, then driving efficiency is improved, but weight increases
Solution Approach 1:
The transmission system combines four planetary gear sets into a unified structure that shares common shafts (first shaft connecting first and fourth planetary gear sets, fourth shaft connecting second and third planetary gear sets). This merging approach achieves nine forward speeds while minimizing weight by eliminating redundant components that would exist in separate gear set configurations
3Power
If the number of planetary gear sets is increased to achieve more shift stages, then power delivery performance is improved, but power flow efficiency deteriorates
Solution Approach 1:
The control elements are designed with multi-functional capabilities to optimize power flow. The first clutch connects rotational elements from both first and fourth planetary gear sets, while the second clutch connects elements from second and third planetary gear sets. This universal control approach enables efficient torque distribution across multiple gear sets, maintaining high power flow efficiency while delivering improved power performance
Solution Approach 2:
The control elements are positioned and configured to preemptively manage torque flow paths before power enters the planetary gear sets. By pre-establishing connection configurations through the clutches and brakes, the system optimizes power distribution routes, reducing energy losses and improving overall power flow efficiency
Data Source
AI summary
A planetary gear train of an automatic transmission is disclosed to improve power delivery and fuel efficiency by applying six control elements to four planetary gear sets to achieve forward nine speed stages and one reverse speed stage. The planetary gear train includes: an input shaft; an output shaft; first to fourth planetary gear sets each having three rotational elements; four clutches and two brakes as the six control elements; and first to ninth shafts. In particular, the first shaft connects first and eleventh rotational elements, and the input shaft; the second shaft is connected with a second rotational element and selectively connected with the first shaft, the third shaft connects third and fifth rotational elements, and the fourth shaft is connected with a fourth rotational element and fixed to a transmission housing. In addition, the sixth shaft is selectively connected with the second and fifth shafts, respectively.